Potential Zika virus risk estimated for 50 U.S. cities

BOULDER – Key factors that can combine to produce a Zika virus outbreak are expected to be present in a number of U.S. cities during peak summer months, new research shows.The Aedes aegypti mosquito, which is spreading the virus in much of Latin America and the Caribbean, will likely be increasingly abundant across much of the southern and eastern United States as the weather warms, according to a new study led by mosquito and disease experts at the National Center for Atmospheric Research (NCAR).Summertime weather conditions are favorable for populations of the mosquito along the East Coast as far north as New York City and across the southern tier of the country as far west as Phoenix and Los Angeles, according to computer simulations conceived and run by researchers at NCAR and the NASA Marshall Space Flight Center.Spring and fall conditions can support low to moderate populations of the Aedes aegypti mosquito in more southern regions of its U.S. range. Wintertime weather is too cold for the species outside southern Florida and southern Texas, the study found.By analyzing travel patterns from countries and territories with Zika outbreaks, the research team further concluded that cities in southern Florida and impoverished areas in southern Texas may be particularly vulnerable to local virus transmission.Many U.S. cities face potential risk in summer of low, moderate, or high populations of the mosquito species that transmits Zika virus (colored circles). The mosquito has been observed in parts of the United States (shaded portion of map) and can establish populations in additional cities because of favorable summertime meteorological conditions. In addition, Zika risk may be elevated in cities with more air travelers arriving from Latin America and the Caribbean (larger circles). For a high-resolution map, click here or on the image. (Image based on data mapped by Olga Wilhelmi, NCAR GIS program. This image is freely available for media & nonprofit use.) "This research can help us anticipate the timing and location of possible Zika virus outbreaks in certain U.S. cities,” said NCAR scientist Andrew Monaghan, the lead author of the study. “While there is much we still don’t know about the dynamics of Zika virus transmission, understanding where the Aedes aegypti mosquito can survive in the U.S. and how its abundance fluctuates seasonally may help guide mosquito control efforts and public health preparedness.”“Even if the virus is transmitted here in the continental U.S., a quick response can reduce its impact,” added NCAR scientist Mary Hayden, a medical anthropologist and co-author of the study.Although the study does not include a specific prediction for this year, the authors note that long-range forecasts for this summer point to a 40–45 percent chance of warmer-than-average temperatures over most of the continental United States. Monaghan said this could lead to increased suitability for Aedes aegypti in much of the South and East, although above-normal temperatures would be less favorable for the species in the hottest regions of Texas, Arizona, and California.Monaghan stressed that, even if Zika establishes a toehold in the mainland United States, it is unlikely to spread as widely as in Latin America and the Caribbean. This is partly because a higher percentage of Americans live and work in air-conditioned and largely sealed homes and offices.The study is being published today in the peer-reviewed journal PLOS Currents Outbreaks. It was funded by the National Institutes of Health, NASA, and the National Science Foundation, which is NCAR’s sponsor. It was co-authored by scientists at NASA, North Carolina State University, Maricopa County Environmental Services Vector Control Division, University of Arizona, and Durham University.Spreading rapidlyFirst identified in Uganda in 1947, the Zika virus has moved through tropical regions of the world over the past decade. It was introduced into Brazil last year and spread explosively across Latin America and the Caribbean, with more than 20 countries now facing pandemics.About 80 percent of infected people do not have significant symptoms, and most of the rest suffer relatively mild flu- or cold-like symptoms that generally clear up in about a week. However, scientists are investigating correlations between contracting the disease during pregnancy and microcephaly, a rare birth defect characterized by an abormally small head and brain damage.To determine the potential risk in the mainland United States, the research team ran two computer models that simulated the effect of meteorological conditions on a mosquito’s entire lifecycle (egg, larval, pupal, and adult stages) in 50 cities in or near the known range of the species. Monaghan and several team members have studied Aedes aegypti for years because it also carries the viruses that cause dengue and chikungunya.Generally, the mosquitoes need warm and relatively stable temperatures, as well as water-filled containers such as buckets, barrels, or tires, for their eggs to hatch. Once a mosquito bites an infected person, it also needs to live long enough – probably a week or more, depending on ambient temperatures – for the virus to travel from the mosquito's mid-gut to its salivary glands. Once in the saliva, the virus can then be transmitted by the mosquito biting another person.The study results show that, as springtime weather warms, the potential abundance of the mosquito begins to increase in April in the Southeast and some Arizona cities. By June, nearly all of the 50 cities studied have the potential for at least low-to-moderate abundance, and most eastern cities are suitable for moderate-to-high abundance. Conditions become most suitable for mosquito populations in July, August, and September, although the peak times vary by city. Weather conditions in southern and western cities remain suitable as late as November.Even some cities where the Aedes aegypti mosquito has not been detected, such as St. Louis and Denver, have suitable midsummer weather conditions for the species if it were introduced via transport of used tires or by other human activities, according to the computer models.The researchers stressed that additional factors outside the scope of the study could affect populations of the species, such as mosquito control efforts, competition with other mosquito species, and the extent to which eggs can survive in borderline temperatures.The study noted that northern cities could become vulnerable if a related species of mosquito that is more tolerant of cold temperatures, Aedes albopictus, begins to carry the virus.This animation shows the varying extent to which meteorological conditions can favor populations of the Aedes aegypti mosquito, which transmits the Zika virus, in 50 U.S. cities throughout the year. Red dots represent high-abundance conditions, orange represents medium-to-high, yellow represents low-to-medium, and gray represents no significant mosquito population. (Animation based on data from Andrew Monaghan, NCAR. This image is freely available for media & nonprofit use.)Factoring in travel, povertyIn addition to looking at meteorological conditions, the researchers studied two other key variables that could influence the potential for Zika outbreaks: travel from Zika-affected areas and socioeconomic conditions in states that may face abundant mosquito populations.To analyze air travel, the team estimated the number of passengers arriving into U.S. cities on direct flights from airports in 22 Latin American countries and territories listed on the Centers for Disease Control and Prevention’s Zika travel advisory as of January 29.Cities that had both high potential numbers of Aedes aegypti and a large volume of air travelers included Miami, Houston, and Orlando. Since the scientists were able to obtain passenger numbers for direct flights only, they could not estimate the number of passengers continuing on to smaller cities. They noted that the summertime peak in air travel coincides with the peak season in mosquito abundance.The study also estimated that nearly five times as many people cross the U.S.-Mexico border per month than arrive by air in all 50 cities. This could indicate a high potential for transmission in border areas from Texas to California, although the Zika virus has not been widely reported in northern Mexico.Those border areas, as well as other parts of the South where the mosquitoes are expected to be abundant, have a high percentage of households living below the poverty line, according to 2014 U.S. Census data analyzed by the research team. Lower-income residents can be more exposed to mosquito bites if they live in houses without air conditioning or have torn or missing screens that enable mosquitoes to enter their homes more easily. However, Aedes aegypti populations tend to thrive in densely populated urban areas, while some of the most impoverished areas are rural.“The results of this study are a step toward providing information to the broader scientific and public health communities on the highest risk areas for Zika emergence in the United States,” said Kacey Ernst, an epidemiologist at the University of Arizona and co-author of the study. “We hope that others will build on this work as more information becomes available. All areas with an environment suitable to the establishment of Aedes aegypti should be working to enhance surveillance strategies to monitor the Aedes aegypti populations and human populations for disease emergence.”“This research highlights the complex set of human and environmental factors that determine whether a mosquito-borne disease is carried from one area to another, and how severely it affects different human populations,” said Sarah Ruth, program director in the National Science Foundation’s Division of Atmospheric and Geospace Sciences. “By integrating information on weather, travel patterns, mosquito biology, and human behavior, the project team has improved our ability to forecast, deal with, and possibly even prevent future outbreaks of Zika and other serious diseases.”About the articleTitle: On the seasonal occurrence and abundance of the Zika virus vector mosquito Aedes aegypti in the contiguous United StatesAuthors: Andrew Monaghan, Cory Morin, Daniel Steinhoff, Olga Wilhelmi, Mary Hayden, Dale Quattrochi, Michael Reiskind, Alun Lloyd, Kirk Smith, Christopher Schmidt, Paige Scalf, and Kacey ErnstJournal: PLOS Currents Outbreaks

Dengue and climate: Scientists tackle the nuances

August 4, 2015 | For more than a decade, scientists have known that the mosquitoes transmitting dengue fever have been moving from the tropics north into the United States—as far north as New Jersey, with outbreaks in Brownsville, Texas, and heavily touristed Key West, Florida. Now NCAR scientists and their colleagues are learning more about why certain areas are prone to dengue outbreaks while others aren’t, and what factors can best predict the future impact of the disease also known as “breakbone fever." “Climate change is an important factor in the development of the mosquitoes that carry dengue viruses, but it may not be the primary driver of dengue,” said NCAR scientist Mary Hayden, a medical anthropologist. NCAR scientist Mary Hayden takes samples from a water-filled tire in Brownsville, Texas, to test for the mosquito species that transmits dengue fever. Brownsville has experienced dengue outbreaks in 2005 and 2013. (Photo courtesy Mary Hayden, NCAR.) “Climate change is important at large scales, but as you move to specific locations, it becomes one of many factors that affect disease and transmission risk,” added meteorologist Andrew Monaghan, another member of the NCAR team. He explained that other factors include the areas where mosquitoes breed and develop, local disease prevention efforts, socioeconomic conditions, and human population density. To better understand this complicated issue, NCAR experts in climate, weather, disease, and behavioral science have been examining dengue for nearly a decade, in collaboration with various universities and federal agencies, including the Centers for Disease Control and Prevention. "We've built a multidisciplinary team, which is what's needed to understand how all the factors interact," said Hayden. A newly global disease A half-century ago, less than 10 countries experienced serious dengue epidemics. Dengue viruses, transmitted by several species of Aedes mosquitoes, are now passed from human to mosquito to human at endemic levels in more than 100 countries, according to the World Health Organization. Symptoms typically include a sudden high fever, severe headache, and joint pain. Estimates of annual infections range from 50 million to 400 million people worldwide, with about 500,000 hospitalized. Young children especially are vulnerable. There are about 12,500 deaths each year from dengue, WHO reports. An outbreak in Key West in 2009–2010 represented the first dengue cases in the continental United States outside the Texas-Mexico border region since 1945. The number of cases in this country remains small but several recent outbreaks, including one in Brownsville, Texas, in 2013, have health officials concerned. Hayden and others believe dengue is underreported in the United States, in part because of low awareness. The good news is that research and fieldwork to date indicate that it takes a nearly “perfect storm” of climatic, socioeconomic, and human behavioral factors for the mosquito to thrive in the United States, Hayden said. For optimal development, the mosquitoes want to be in a “sweet spot” of 77 to 90 degrees Fahrenheit (25 to 32 degrees Celsius) with as few fluctuations as possible, Monaghan said. So even though one would expect dengue fever in Nogales, Mexico—given its prevalence in nearby cities just south—temperatures, especially at night, typically are cool enough to thwart an outbreak. The mosquito depends on humans for “blood meals,” but also is effective at hitching rides on trucks, cargo ships, and the like. In South America, Hayden and colleagues want to study the surprising emergence of dengue in the Galapagos Islands, off the coast of Ecuador. Hayden spends much of her time examining how human perceptions and behavior can increase disease risk. She has conducted household surveys in the U.S. dengue hot spots of Brownsville and Key West. That research included hunting for outdoor surfaces favorable to mosquito breeding, such as old tires, tarps, and other objects that capture standing water. In 2012, Hayden and colleague Kacey Ernst (University of Arizona) conducted a survey of 400 Key West households that showed an abundance of potential breeding sites. Monaghan said scientists increasingly are simulating dengue’s future impact—taking climate change, population trends, and other factors into account. He would like to expand these computer models to include the effectiveness of local interventions such as public awareness education and the use of biological agents to kill larvae and adult mosquitoes. “We’re interested in learning how we can best intervene to reduce the threat of dengue outbreaks,” he said. “As climate change continues, we're looking for the drivers we can control at the local level.” Writer/Contact Jeff Smith Collaborators Centers for Disease Control and Prevention University of Arizona FundersNational Science FoundationNational Institutes of Health

Exposure of U.S. population to extreme heat could quadruple by mid-century

BOULDER – U.S. residents' exposure to extreme heat could increase four- to six-fold by mid-century, due to both a warming climate and a population that's growing especially fast in the hottest regions of the country, according to new research.  The study, by researchers at the National Center for Atmospheric Research (NCAR) and the City University of New York (CUNY), highlights the importance of considering societal changes when trying to determine future climate impacts. "Both population change and climate change matter," said NCAR scientist Brian O'Neill, one of the study’s co-authors. "If you want to know how heat waves will affect health in the future, you have to consider both." Extreme heat kills more people in the United States than any other weather-related event, and scientists generally expect the number of deadly heat waves to increase as the climate warms. The new study, published May 18 in the journal Nature Climate Change, finds that the overall exposure of Americans to these future heat waves would be vastly underestimated if the role of population changes were ignored. The total number of people exposed to extreme heat is expected to increase the most in cities across the country's southern reaches, including Atlanta, Charlotte, Dallas, Houston, Oklahoma City, Phoenix, Tampa, and San Antonio. The research was funded by the National Science Foundation, which is NCAR's sponsor, and the U.S. Department of Energy.  Climate, population, and how they interact For the study, the research team used 11 different high-resolution simulations of future temperatures across the United States between 2041 and 2070, assuming no major reductions in greenhouse gas emissions. The simulations were produced with a suite of global and regional climate models as part of the North American Regional Climate Change Assessment Program.  Using a newly developed demographic model, the scientists also studied how the U.S. population is expected to grow and shift regionally during the same time period, assuming current migration trends within the country continue. Total exposure to extreme heat was calculated in "person-days" by multiplying the number of days when the temperature is expected to hit at least 95 degrees by the number of people who are projected to live in the areas where extreme heat is occurring. The results are that the average annual exposure to extreme heat in the United States during the study period is expected to be between 10 and 14 billion person-days, compared to an annual average of 2.3 billion person-days between 1971 and 2000. This graphic illustrates the expected increase in average annual person-days of exposure to extreme heat for each U.S. Census Division when comparing the period 1971–2000 to the period 2041–2070. Person-days are calculated by multiplying the number of days when the temperature is expected to hit at least 95 degrees by the number of people who are projected to live in the areas where extreme heat is occurring. The scale is in billions. (©UCAR. This image is freely available for media & nonprofit use.) Of that increase, roughly a third is due solely to the warming climate (the increase in exposure to extreme heat that would be expected even if the population remained unchanged). Another third is due solely to population change (the increase in exposure that would be expected if climate remained unchanged but the population continued to grow and people continued to moved to warmer places). The final third is due to the interaction between the two (the increase in exposure expected because the population is growing fastest in places that are also getting hotter). "We asked, 'Where are the people moving? Where are the climate hot spots? How do those two things interact?'" said NCAR scientist Linda Mearns, also a study co-author. "When we looked at the country as a whole, we found that each factor had relatively equal effect." At a regional scale, the picture is different. In some areas of the country, climate change packs a bigger punch than population growth and vice versa. For example, in the U.S. Mountain region—defined by the Census Bureau as the area stretching from Montana and Idaho south to Arizona and New Mexico—the impact of a growing population significantly outstrips the impact of a warming climate. But the opposite is true in the South Atlantic region, which encompasses the area from West Virginia and Maryland south through Florida. Exposure vs. vulnerability Regardless of the relative role that population or climate plays, some increase in total exposure to extreme heat is expected in every region of the continental United States. Even so, the study authors caution that exposure is not necessarily the same thing as vulnerability. "Our study does not say how vulnerable or not people might be in the future," O'Neill said. "We show that heat exposure will go up, but we don't know how many of the people exposed will or won't have air conditioners or easy access to public health centers, for example." The authors also hope the study will inspire other researchers to more frequently incorporate social factors, such as population change, into studies of climate change impacts. "There has been so much written regarding the potential impacts of climate change, particularly as they relate to physical climate extremes," said Bryan Jones, a postdoctoral researcher at the CUNY Institute for Demographic Research and lead author of the study. "However, it is how people experience these extremes that will ultimately shape the broader public perception of climate change." About the article Title: "Future population exposure to U.S. heat extremes"Authors: Bryan Jones, Brian C. O’Neill, Larry McDaniel, Seth McGinnis, Linda O. Mearns, and Claudia TebaldiPublication: Nature Climate Change  

Biting back: Scientists aim to forecast West Nile outbreaks

BOULDER – New research has identified correlations between weather conditions and the occurrence of West Nile virus disease in the United States, raising the possibility of being able to better predict outbreaks. The study, by researchers with the National Center for Atmospheric Research (NCAR) and the Centers for Disease Control and Prevention (CDC), finds strong correlations across much of the country between an increased occurrence of West Nile virus disease and above average temperatures in the preceding year. The scientists also find that precipitation influences subsequent disease outbreaks, although the impacts vary by region. The weather may influence West Nile virus activity by affecting the breeding habitats and abundance of Culex species mosquitoes, which transmit the virus. The weather may also have other impacts, such as affecting populations of infected birds that pass on the virus to mosquitoes. “We've shown that it may be possible to build a system to forecast the risk of West Nile virus disease several weeks or months in advance, before the disease begins to peak in summer,” said lead author Micah Hahn, a scientist with both NCAR and CDC. “Having advance warning can help public health agencies plan and take additional steps to protect the public.” The study appears this week in the American Journal of Tropical Medicine and Hygiene. It was funded by CDC and the National Science Foundation, which is NCAR’s sponsor. Tracking a deadly virus About 80 percent of people who are infected with West Nile virus do not get sick, and most of the rest have a mild illness with fever. Less than 1 percent of people infected with West Nile virus develop serious infections of the brain or spinal cord. Since West Nile virus was first detected in the United States in 1999, there have been about 40,000 cases throughout the country in which the sickness progressed to the point where it was reported. It has caused more than 1,600 deaths. There is no vaccine or specific treatment for the disease. But predicting outbreaks could enable local officials to take action to reduce the number of mosquitoes and alert the public to take extra precautions to avoid being bitten. This map shows the average number of annual cases of West Nile virus with neurological symptoms that were reported to the CDC from 1999 to 2013. Close to 40,000 cases were reported during that period, with more than 1,600 deaths. (Source: ArboNET, Arboviral Diseases Branch, Centers for Disease Control and Prevention.) Previous research into possible links between West Nile virus disease and weather has focused on limited geographic areas or relatively short time periods. For the new study, Hahn and her co-authors conducted a detailed statistical analysis of weather impacts on the disease in counties across the contiguous United States from 2004 through 2012. They used county-level West Nile virus neurologic disease reports and local temperature and precipitation data. The researchers found that warmer temperatures were strongly correlated with higher rates of West Nile virus disease throughout most of the country. The effect was most pronounced in counties in the Northeast and Southeast, where an annual temperature increase of 1 degree Celsius (1.8° Fahrenheit) above their 2004-2012 average meant a fivefold increased likelihood of an above-average outbreak of West Nile. The same temperature increase approximately doubled the risk for much of the rest of the country, including the mid-Atlantic, Midwest, and Great Plains. But temperature increases seemed to have no impact in parts of the West. Warmer temperatures might increase the incidence of disease by accelerating development of mosquito larvae, accelerating adult mosquito reproduction, and allowing greater survival rates for eggs and adult mosquitoes during the winter. Dry in the East, wet in the West When it came to precipitation, the impacts were more complex. In the eastern United States, drier-than-normal fall and spring seasons correlated with above-average West Nile virus disease outbreaks the following summer. But in much of the West, the picture was different: wetter-than-average winters correlated with above-average outbreaks. For example, Western counties that received 100 millimeters (about 4 inches) of precipitation above average generally had a 1.4 times higher likelihood of an above-average West Nile virus outbreak. Why the difference between the eastern and western United States? The authors suggest that the Culex species mosquitoes that inhabit the East may thrive under drier conditions, when stagnant pools of water provide optimal breeding habitats and there are few downpours that would flush out larvae from catch basins. In contrast, higher-than-normal precipitation in the arid West could create temporary pools of fresh, sunlit water in irrigated fields—a breeding location favored by the western Culex species. Overall, the study paints a variegated picture of the links between temperature, precipitation, and West Nile virus disease occurrence. For example, the disease in the Northern Rockies and northwestern Plains appears to increase with drier conditions—making that region more similar to the East in terms of the virus. While the reasons are unclear, the paper speculates that it may have to do with larger snowpack that causes moister spring soil conditions. The authors stress that a prediction system would need to consider regional variations. It would also need to consider non-weather factors, such as the percentage of elderly people living in the county (who are more likely to develop neurologic symptoms if infected) and past outbreaks of West Nile virus disease (which can increase immunity in local bird populations and therefore reduce subsequent infection rates in people). About the paper Title: Meteorological conditions associated with increased incidence of West Nile virus disease in the United States, 2004–2012 Authors: Micah B. Hahn, Andrew J. Monaghan, Mary H. Hayden, Rebecca J. Eisen, Mark J. Delorey, Nicole P. Lindsey, Roger S. Nasci, and Marc Fischer Journal: American Journal of Tropical Medicine & Hygiene

Predicting the Lyme disease season

July 9, 2014 | Warmer temperatures, higher humidity, and less rain are correlated with an earlier start and peak of each year’s Lyme disease season, researchers have found. Using the dates of Lyme disease cases reported to the U.S. Centers for Disease Control and Prevention (CDC) and meteorological data from 1992 to 2007, researchers at NCAR and the CDC have for the first time analyzed the timing of the warm-season ramp-up of Lyme disease transmission. The research should help forecasters develop predictions of the onset and peak of future Lyme disease seasons. More than 20,000 cases of Lyme disease are reported in the United States each year. On this map, one dot is placed randomly within the county of residence for each confirmed case in 2011 reported to the U.S. Centers for Disease Control and Prevention for locations within the map domain. In 2012, 95% of U.S. cases of Lyme disease were reported from just 12 states; all are shown on this map. Though Lyme disease cases have been reported in nearly every state, cases are reported based on the county of residence, not necessarily the county of infection. (Image courtesy CDC.) Lyme disease is a tick-borne illness primarily found in the northeastern United States (from southern Maine to northern Virginia) and Wisconsin and Minnesota. The start and peak of the human infection season occur earlier in the spring in southern states, and later in northern states, but vary overall from year to year. The researchers found that for all but the northernmost states, higher cumulative temperatures above a baseline of 50°F (10°C) measured from the beginning of the year were reliably associated with an earlier start to the Lyme disease season. For all regions, a greater amount of precipitation accumulating from the start of the year was consistently associated with a later beginning to the season. The start of the Lyme disease season (defined as the week the number of Lyme disease cases increased most rapidly) varied by up to 6 weeks in the same state over the 16-year period analyzed. The average season begins in late May and lasts for 14 weeks. The team of researchers, led by Sean Moore, a former public health and climate postdoctoral fellow at NCAR and the CDC, published the findings earlier this year in the American Journal of Tropical Medicine and Hygiene. NCAR scientist Andrew Monaghan supervised the team’s meteorological analysis. “While you can predict the Lyme season more accurately as the beginning of the season nears, we found that, by looking at the daily temperatures out to the 10th week of the year, we could predict the start of the season almost as well as waiting until the 20th week,” Monaghan said. With more validation, the CDC could eventually use the analysis to provide public warnings about the likelihood of encountering ticks bearing Lyme disease, he said. Lyme disease is the most common vector-transmitted disease in the United States. It may progress from causing a characteristic bull’s-eye rash to triggering serious neurological or heart problems, meningitis, or arthritis, if left untreated. It is caused by a bacterial spirochete that is primarily transmitted by Ixodid ticks. The ticks pass on the bacteria when they attach to mammals to obtain the blood they need to complete each of three developmental stages. Nymphal ticks, which are about the size of a poppy seed, cause most of the cases of Lyme disease in humans because their small size makes them very hard to find and remove. Nymphal ticks develop faster with warmer temperatures, and more actively seek hosts for a blood meal between late spring and fall when there are warmer temperatures, higher humidity, and the absence of heavy precipitation. These same weather conditions are also ones that encourage people to spend more time outside, the researchers noted. The availability of other hosts, such as rodents and deer, also plays a role in maintaining tick populations and may increase the transmission of Lyme disease. ContactDavid Hosansky, NCAR/UCAR Communications ResearchersSean Moore (former NCAR/CDCpostdoctoral researcher,now at Johns HopkinsSchool of Public Health)Rebecca Eisen, CDCPaul Mead, CDCAndrew Monaghan, NCAR Collaborating institutionsNational Center for Atmospheric ResearchU.S. Centers for Disease Control and Prevention (CDC) Funders CDC National Science Foundation  

Predicting flu season

December 20, 2013 | Using methods from weather and climate forecasting, researchers have developed a forecasting system for the flu that can incorporate real-time data to predict the week that influenza levels will peak. A research team that included NCAR’s Alicia Karspeck made 12 weekly forecasts for 108 U.S. cities during the 2012-13 flu season, and found the system accurately predicted the outbreak’s peak for 60 percent of the cities weeks in advance. People wear face masks in Mexico during a 2009 outbreak of the flu. Scientists have created a pilot system to forecast flu outbreaks. (Photo by Henry Merino, Wikimedia Commons.) The researchers, led by Jeffrey Shaman of Columbia University, combined a model of disease transmission with data from Google Flu Trends, which tracks internet searches on flu-related terms, and with data from the Centers for Disease Control, which tracks the number of people testing positive for flu. Karspeck focused on advanced data assimilation techniques, which combined observations with computer simulations to estimate the current state of flu cases. This enabled the researchers to tune the model with real-time data as the season progressed. The study was published earlier this month in Nature Communications. Karspeck’s usual work is with the data assimilation system for the ocean component of the Community Earth System Model, a global climate model that incorporates data about the atmosphere, land surface, ocean and sea ice to make long-term climate predictions. But five years ago, while at a conference, she had a discussion about forecasting with a former graduate school classmate who was creating a model of influenza outbreaks. “It’s a sort of technology transfer, in the sense that we have a very strong group here at NCAR that works in data assimilation to support forecast initialization,” Karspeck said. “We took the same technology and methodologies and crossed disciplines.” Data assimilation allows the model to reflect actual influenza conditions in a population, she said, such as the number of susceptible people, the number of people who already have the flu, and those who have some immunity to it. Data assimilation was also used to tune the model in real time, so that it could better reflect population and virus characteristics that are relevant to the evolving outbreak. The researchers believe that this leads to more accurate predictions as the season progresses. The number of people who have the flu usually peaks sometime between December and April. The researchers will test the model again this winter and plan to validate the forecasts after the season ends. Having advance notice of when the number of people infected will rapidly increase could help reduce the severity of flu outbreaks by motivating more people to be vaccinated in advance, or giving officials the option to close schools or cancel events that could facilitate flu transmission. Influenza is associated with the deaths of anywhere from 3,000 to 49,000 people each year in the United States. Jeffrey Shaman, Alicia Karspeck, Wan Yang, James Tamerius, Marc Lipsitch, Real-time influenza forecasts during the 2012–2013 season, Nature Communications, 4, December 3, 2013. doi:10.1038/ncomms3837

Google and the flu

Bob Henson • November 30, 2012 | What if we could use the data from fevered searches for flu information on the Web, plus humidity observations, to help predict the course of an outbreak? If new research lives up to its promise, we’ll soon be able to do just that. Millions of Americans get flu vaccinations each year, but other millions don't. Vaccination rates are one of many variables that help determine the course of an influenza outbreak. (©UCAR. Photo by Carlye Calvin. This image is freely available for media & nonprofit use.*) This intriguing advance is outlined in a paper this week in Proceedings of the National Academy of Sciences (PNAS) and highlighted in an NCAR news release. The study authors are Jeff Shaman, a biologist and atmospheric scientist by training who works at Columbia University’s Mailman School of Public Health, and NCAR’s Alicia Karspeck, an atmospheric scientist and expert on bringing data into computer models—the not-so-simple task known as data assimilation. The core data for the project are geographic patterns that emerge as people use Google to search for influenza-related information. Perhaps not surprisingly, these searches are strongly correlated with local spikes in flu prevalence, so they serve as a real-time monitoring tool, viewable at Google Flu Trends (part of, the company’s philanthropic arm). The trick for Shaman and Karspeck was to get these data into a predictive model in a useful way. To do this, they called on one of the most popular data assimilation techniques used in weather forecasting (more on this below). And their predictive model includes information on the kind of weather that helps flu to spread—which might not be the weather you imagine. A virus that likes it dry For more than half a century, laboratory work and incidence patterns have suggested that influenza viruses tend to spread more readily when the air is dry. However, pinning down the effect has proven difficult. Some researchers suspected that the reason for influenza’s clear wintertime peaks might be school schedules, cold-weather gatherings indoors, or other nonmeteorological factors. When it comes to weather, “people had been looking exclusively at relative humidity and temperature,” says Shaman. “They’d only seen marginal relationships between both of these markers and influenza.” People often associate influenza with damp, chilly weather. In fact, the virus is more likely to be transmitted when the amount of moisture in the air is unusually low. (©UCAR. Photo by Carlye Calvin. This image is freely available for media & nonprofit use.*) It occurred to Shaman that a more powerful weather variable might be absolute humidity (AH), the literal amount of moisture in the air. Absolute humidity doesn’t change when an air parcel is heated or cooled, while relative humidity does. In a 2009 study published in PNAS, Shaman and colleagues showed that AH bore a much stronger and more consistent relationship than did relative humidity to virus survival and flu transmission rates. Since AH doesn’t change when you go indoors (unless you have a humidifier or air conditioner), whatever influence it has on the flu virus would be consistent in both environments. Interestingly, the virus itself is borne on tiny droplets, so exactly why it would spread most readily in a dry atmosphere remains a mystery. “I’ve seen about five competing hypotheses,” says Shaman. Whatever the explanation, Shaman found that flu epidemics were somewhat more likely to occur several weeks after a region experienced relatively low AH values. This was a useful building block for a predictive model of influenza spread, which Shaman introduced in a 2010 PloS Biology paper. But there’s much more than weather driving flu epidemics. While AH can shape the climatological signature of flu in temperate regions, he says, “what it can’t do on its own without data assimilation is produce individual outbreaks that match observations.” To do this, Shaman’s model would also need to incorporate current information on what the virus was actually doing, and then extend that behavior into the future. Taming uncertainty In 2009, Shaman discussed the unfolding research over dinner with Karspeck at the annual meeting of the American Geophysical Union (this year’s conference kicks off next week). “Alicia and I were officemates in grad school at Columbia, so I knew she was doing data assimilation work,” he says. “I wanted to build on that first flu paper and develop some sort of predictive model. She said that sounded like a really good project for data assimilation.” The challenge was to keep Shaman’s flu-prediction model from running out of control. Just as small, unobservable weather features can lead to big forecast errors over time—often referred to as the “butterfly effect,” though that analogy should be used with care—there are aspects of flu transmission that can’t be easily measured but that greatly influence the odds of an epidemic. These range from how many people in a given area get flu vaccinations to how often people travel elsewhere and bring a virus back with them. Karspeck had a particular tool in mind for handling this uncertainty: the ensemble Kalman filter. Introduced to meteorology in the 1990s, it’s become one of the leading methods for bringing large datasets into numerical weather forecast models, especially when there are other variables that can’t be directly observed in a quantitative way. Clouds are a good example: their highly variegated nature can’t be portrayed with precision in a model, so clouds are instead parameterized (estimated) based on temperature, humidity, and other observable factors. “There are elements in flu transmission that you can observe and those you can’t,” Karspeck explains. “One of the powerful aspects of data assimilation in general, and our method in particular, is the ability to estimate those unknown pieces of information, which turn out to be important in making forecasts.” This continually updated graph shows the current status of U.S. flu trend and compares it to recent years. (Image courtesy In a nutshell, the ensemble Kalman filter allows a forecast from the flu prediction model to be “nudged” toward the most recent search data, which serve as a proxy for flu incidence. In addition to this basic task, the ensemble Kalman filter uses a more sophisticated strategy to track the unobserved variables (such as the number of flu-susceptible people) as well as the observed ones (Google searches) This allows the model to bring a complete picture of the social and physical setting for flu transmission forward in time. “We’re inferring all of this other information by using estimates of the number of infected people,” Karspeck says. (The AH component of the model is handled separately from the Kalman filter.) To use a loose and somewhat goofy analogy, imagine you’re off on a blind date. You start out with a set of expectations about what certain actions from your date—a smile, a raised eyebrow, a bit of personal history—might mean for the future. Your mental map relating current observations to possible outcomes is akin to the flu-prediction model, except the latter is quantitative and probabilistic. You also know that you can’t read your date’s mind, but you can use the behaviors you observe to infer what she or he is thinking. In this rough analogy, the ensemble Kalman filter relates each observed behavior to each unobserved thought. As the night goes on, the clues you notice will tend to push your future scenarios closer to each other and to what’s really happening in your date’s mind. Romance might not be a practical setting for using the real-life ensemble Kalman filter, but the tool has potential in many other areas, according to Jeff Anderson, who directs the NCAR-based Data Assimilation Research Testbed. This group of about a half dozen scientists explores new ways of doing assimilation and helps other researchers apply those techniques. Anderson led the creation of the version of the ensemble Kalman filter used in the Shaman-Karspeck study. “We’ve already had some users try out ensemble filters in a variety of other fields, such as economic forecasting,” says Anderson. “They open up the possibility of addressing very large problems, and they make it much easier to use complex prediction models.” One case where ensemble filters have especially great untapped potential, according to Anderson, is election forecasting. Shaman, Karspeck, and colleagues plan to continue their journey toward what they hope will become a practical real-time system for predicting flu outbreaks weeks in advance. First, though, will come more testing over different regions and longer time periods in order to validate the model’s performance. “Over time, as we do more and more of these studies, we’ll be able to do more robust validation,” says Karspeck. A couple of factors will ease the way. The data involved are readily available to the public, and although the interrelationships are complex, the eventual number crunching is quite manageable. As Karspeck notes, “all this work was done on our laptops.” Related News Flu outbreaks predicted with weather forecast techniques

Flu outbreaks predicted with weather forecast techniques

BOULDER—Scientists at Columbia University and the National Center for Atmospheric Research have adapted techniques used in modern weather prediction to generate local forecasts of seasonal influenza outbreaks. By predicting the timing and severity of the outbreaks, this pilot system can eventually help health officials and the general public better prepare for them. People wear face masks in Mexico during a 2009 outbreak of the flu. Scientists have created a pilot system to forecast flu outbreaks. (Photo by Henry Merino, Wikimedia Commons.) The study, published this week in the Proceedings of the National Academy of Sciences, was funded by the National Institutes of Health and the Department of Homeland Security. NCAR's sponsor is the National Science Foundation. From year to year, and region to region, there is huge variability in the peak of flu season, which can arrive in temperate areas of the Northern Hemisphere as early as October or as late as April. The new forecast system can provide “a window into what can happen week to week as flu prevalence rises and falls,” says lead author Jeffrey Shaman, an assistant professor of Environmental Health Sciences at Columbia’s Mailman School of Public Health. In previous work, Shaman and colleagues had found that wintertime U.S. flu epidemics tended to occur following very dry weather. Using a prediction model that incorporates this finding, Shaman and co-author Alicia Karspeck, an NCAR scientist, used Web-based estimates of flu-related sickness from the winters of 2003–04 to 2008–09 in New York City to retrospectively generate weekly flu forecasts. They found that the technique could predict the peak timing of the outbreak more than seven weeks in advance of the actual peak. “Analogous to weather prediction, this system can potentially be used to estimate the probability of regional outbreaks of the flu several weeks in advance,” Karspeck says. “One exciting element of this work is that we've applied quantitative forecasting techniques developed within the geosciences community to the challenge of real-time infectious disease prediction. This has been a tremendously fruitful cross-disciplinary collaboration.” Up next: your local flu forecast In the future, such flu forecasts might conceivably be disseminated on the local television news along with the weather report, says Shaman. Like the weather, flu conditions vary from region to region; Atlanta might see its peak weeks ahead of Anchorage. “Because we are all familiar with weather broadcasts, when we hear that there is an 80 percent chance of rain, we all have an intuitive sense of whether or not we should carry an umbrella,” Shaman says. “I expect we will develop a similar comfort level and confidence in flu forecasts and develop an intuition of what we should do to protect ourselves in response to different forecast outcomes.” A flu forecast could prompt individuals to get a vaccine, exercise care around people sneezing and coughing, and better monitor how they feel. For health officials, it could inform decisions on how many vaccines and antiviral drugs to stockpile, and in the case of a virulent outbreak, whether other measures, like closing schools, is necessary. “Flu forecasting has the potential to significantly improve our ability to prepare for and manage the seasonal flu outbreaks that strike each year,” says Irene Eckstrand of the National Institutes of Health’s National Institute of General Medical Sciences. Worldwide, influenza kills an estimated 250,000 to 500,000 people each year. The U.S. annual death toll is about 35,000. The seed of the new study was planted four years ago in a conversation between the two researchers, in which Shaman expressed an interest in using models to forecast influenza. Karspeck “recommended incorporating some of the data assimilation techniques used in weather forecasting to build a skillful prediction system,” remembers Shaman. In weather forecasting, real-time observational data are used to nudge a numerical model to conform with reality, thus reducing error. Applying this method to flu forecasting, the researchers used near-real-time data from Google Flu Trends, which estimates outbreaks based on the number of flu-related search queries in a given region. Going forward, Shaman will test the model in other localities across the country using up-to-date data. “There is no guarantee that just because the method works in New York, it will work in Miami,” Shaman says. About the article Title:  Forecasting seasonal outbreaks of influenza Authors:  Jeffrey Shaman and Alicia Karspeck Journal:  Proceedings of the National Academy of Sciences (Abstract)

A splash of reality

August 13, 2012 | When it's clean, plentiful, accessible, and controllable, water is easy to take for granted. Things are different when the supply becomes a torrent—or a trickle. For much of the United States, the summer of 2012 has been one of those times. The most extensive U.S. drought in almost 60 years has enveloped some of the nation’s most productive farmland. The impacts go well beyond agriculture: in parts of the Midwest, shifting soils are cracking building foundations and prompting water restrictions more familiar in California than Indiana. In this image, the large bubble atop the central United States represents the volume of all of Earth's water, including oceans and groundwater. The smaller bubble atop Kentucky denotes the volume of Earth's freshwater (groundwater, lakes, swamp water, and rivers), while the tiny bubble over Georgia represents lakes and rivers alone. (Image courtesy USGS Water Science Photo Gallery.) Even as public attention comes and goes, water is consistently Topic A for a wide-ranging group of researchers. Hydrologists have teamed with meteorologists, climate scientists, and engineers to analyze flood, drought, and water storage. The last decade has seen breakthroughs in the mapping of glaciers and aquifers, plus a steadily improving picture of how water flows into and out of the atmosphere. In the United States, there’s a growing network of drought specialists and an enhanced warning system for regional drought. These advances are running neck and neck with ominous trends. Earth’s warming climate threatens to shunt precipitation toward polar regions and the tropics, with an increased risk of drought at latitudes where billions of people live. Higher temperatures will tend to pull more water out of soils. Even without climatic change, the global demand for water continues to grow hand in hand with population. Water access already varies hugely among countries, and major U.S. aquifers are being depleted at a worrisome pace. As portrayed by the National Drought Mitigation Center, the “hydro-illogical cycle” describes how drought, as a slow-moving natural disaster, tends to emerge under the radar screen, then intensify until people can no longer ignore it or wish it away—until it rains again. (Illustration ©National Drought Mitigation Center.) As they work to understand the hydrologic cycle that sustains our water supply, and the evolution of climate factors that may change it, scientists and policy experts at NCAR and elsewhere bemoan what’s been dubbed the “hydro-illogical cycle,” where pulses of public concern triggered by drought evaporate as soon as the rains return. “We ignore drought until the situation is dire, lament the impacts, justifiably call for help, and clamor for emergency funding,” said J.D. Strong, executive director of the Oklahoma Water Resources Board, in written testimony before Congress on July 25 (see PDF). “But invariably it rains, at which point we forget there was ever a problem and go back to business as usual. We must break this cycle.” In this special report, we take a closer look at water availability and the science that's under way at NCAR, UCAR member universities, and a variety of other partners to help us predict its course. Less water than it seems With more than 70% of Earth covered by oceans, it’s impressive how small the supply of freshwater is by comparison—only about 2 to 3% of the planet’s total water (see graphic). More than two-thirds of that freshwater is locked up in polar ice sheets. Much smaller amounts lie in ice caps and glaciers at lower latitudes, where people can access meltwater. Most of the world’s remaining freshwater is held in deep, inaccessible underground aquifers and within the soil itself. Less than 1% of all global freshwater is readily available in rivers, reservoirs, lakes and shallow aquifers, according to a University of Michigan report. As for the atmosphere, it’s not so much a home for water as a highway for it, according to NCAR's Kevin Trenberth, who heads the scientific steering committee for a major international effort to map the world's energy and water cycles (see sidebar at bottom). According to Trenberth, a typical molecule of water vapor enters the atmosphere from the ocean and spends 8 to 9 days in the air before it returns earthward as rain or snow and flows toward the ocean. At that point, the molecule is usually hundreds or even thousands of miles from the place where it evaporated. Earth’s water is perpetually in motion through the global hydrological cycle, which involves ocean, land, clouds, lakes and rivers, plants, snow, and ice. (© UCAR. UCAR Digital Image Library.) It’s a major task for scientists simply to map out how much water exists at each point in this hydrologic cycle. River flows and reservoir levels are monitored around the world, but many nations are hesitant to release the data for research. Moreover, experts have warned for years that the longstanding network of river gauges in many areas, including the United States, is deteriorating. Measuring evapotranspiration (ET)—the process of water transpiring from plants and evaporating from soil, pavement, and other surfaces into the air—is a challenge of its own. About two-thirds of all rain and snow that falls on land areas ends up entering the atmosphere this way. But there’s not yet a gold-standard measurement technique for ET, and variations in space and time remain poorly mapped. There’s been some promise in combining land-based measurements of ET at specially equipped sites with satellite-based estimates over broader regions. More than a dozen institutions from eight nations have been working over the last several years to evaluate such ET datasets in a project called LandFLux-EVAL. And a team led by NASA’s Matthew Rodell used new ET data to balance the water budgets for seven river basins in Africa, Europe, and North and South America. Evapotranspiration (ET)—the amount of water vapor entering the air from sources other than oceans—varies dramatically across the United States, as shown in this map of total ET for the 2007 growing season (May 1–September 30). In parts of the Deep South, ET averaged as much as 15 mm (0.6 inches) per week. The map was prepared by Baburao Kamble as part of a project to assess ET on a weekly basis using data from NASA’s MODIS satellite. (Image courtesy Baburao Kamble, University of Nebraska Lincoln.) Trenberth and colleagues are using a variety of datasets to put together energy and moisture budgets­ on a continent-by-continent basis, depicting flows in and out of each part of the Earth system over the lifecycle of various ingredients. “We’re trying to see how well we can complete the budget not only for the average but for each month,” says Trenberth, who plans to report on the work in December at the annual meeting of the American Geophysical Union. “I think we may be closer than anyone has been so far.”  Computers and water It’s not only long-term budgets that pose challenges when it comes to modeling the flow of water. For short-term weather models, the emphasis is on correctly depicting the timing and location of rain and snow. This depends on a variety of model aspects, including how observations are assimilated in the model and how well the land surface is depicted, according to NCAR’s Jimy Dudhia. He’s one of the lead developers of ARW, the advanced research version of the multiagency Weather Research and Forecasting model. During 2012 hurricane modeling exercises, researchers used the advanced research version of the Weather Research and Forecasting model (NCAR WRF-ARW) to track Hurricane Ernesto as it weakened and moved inland across southern Mexico. This forecast, issued for 0900 UTC on August 14, projected that more than 204 millimeters (8 inches) of rainfall would fall across some areas (shown in white) over the preceding 111 hours. In this version of the model, the spacing between grid points is 4 kilometers (2.5 miles). Click to enlarge. (Image courtesy NCAR/NESL/MMM.) Dudhia adds that short-term models serve as a critical tool in predicting the risk of flash floods. “This is a challenge because the river flow depends so critically on the position, timing, and intensity of rainfall from thunderstorms, especially over complex terrain,” says Dudhia. Climate models have a different assignment—depicting the trends in water behavior over larger areas and longer periods—so they typically include more aspects of the water cycle, including those that play out gradually. The NCAR-based Community Land Model (CLM), one component of the NSF- and DOE-funded Community Earth System Model (CESM), tracks moisture as it evaporates and transpires, falls as rain or snow, enters river channels, and infiltrates the soil. The CLM also depicts accumulating snowfall and includes a reservoir that simulates the water table. Because of perennial limits on computing power, models like the CLM have often specified glaciers, wetlands, and lakes as elements that remain fixed as the climate evolves. Now, says NCAR land modeler Samuel Levis, “we’re beginning to simulate how some of these water bodies may change in response to simulated changes in the climate.” Another branch of models looks more specifically at where water is headed across and below the land surface, with an eye toward helping water planners. Reed Maxwell (Colorado School of Mines) heads up the ParFlow project, an open-source model of watershed flow that draws on CLM and other components developed at NCAR, Los Alamos National Laboratory, the University of Bonn, and the University of Colorado Boulder. A similar effort in Canada, Hydrogeosphere, was developed at the universities of Laval and Waterloo. At Michigan State University, David Hyndman and colleagues are using integrated hydrologic models to examine how precipitation and temperature may shift as climate change affects the water cycle. (Photo by Kurt Stepnitz, courtesy Michigan State University.) At Michigan State University, a team led by David Hyndman is looking at future changes in the water cycle using MSU’s large-scale, high-resolution Integrated Landscape Hydrology Model. “It’s taking the what-if scenario of projected changes in temperature and precipitation and putting that into something that people understand and relate to,” says Hyndman. Of course, human interventions into the hydrologic cycle can be profound, as people dam rivers, tunnel through mountains, and construct canals to move water from its origins to where it is needed. NCAR scientist David Yates and colleagues at the Stockholm Environment Institute have been developing the Water Evaluation and Planning (WEAP) systems model to help water managers and planners understand the implication of climate on our coupled natural and managed water systems. (See "Who needs glaciers?") Where the moisture is moving As greenhouse gases continue to pile up in a warming atmosphere, the job of tracking and projecting Earth's freshwater gets even more complex. But there’s already a good deal of clarity about the direction of some key water trends. For one thing, higher temperatures are expected to rev up the hydrologic cycle. Warmer air allows more water to evaporate from both land and sea, and that added moisture will tend to intensify rain and snow when and where they form, a trend already being observed in the United States and many other places. On the flip side, the dry spells in between precipitation events will tend to grow longer. Combined with the increased ET from soils, this means an enhanced risk of drought in much of the globe, even where total precipitation may not be changing. New work by NCAR’s Aiguo Dai confirms this outlook.  It’s also become more evident that climate change won’t treat all latitudes equally. Climate models still disagree on how precipitation will change in some regions. However, they concur on the big picture: the dry-leaning zones of the subtropics, centered around latitudes 30°N and 30°S, will tend to expand into the midlatitudes and dry out even further, putting intensified pressure on regional water supplies. For example, the dry, sunny climates found in the southwestern United States and the Middle East have fostered irrigation-dependent agriculture and drawn ever-increasing numbers of residents. Meanwhile, precipitation is expected to increase on average closer to the poles and in the belt of heavy rainfall near the equator that shifts north and south with the seasons. The growth of hydrophilanthropy (Photo courtesy David Kreamer.) Hydrologist David Kreamer (University of Nevada, Las Vegas) is encouraging his peers to look at society’s access to water in the broadest possible terms. At a July 2012 meeting in Boulder, Kreamer pointed out that roughly a billion people lack access to clean drinking water and about 5 million die each year from water-related illnesses. To address these issues, Kreamer and other water experts, including Michael Campana (Oregon State University) and his WaterWired blog, are putting energy toward what Kreamer has dubbed hydrophilanthropy. (See PDF of Kraemer’s 2010 article in the Journal of Contemporary Water Research and Education.) “Solutions to global clean water problems are achievable,” said Kreamer. “I think people who are involved in water have a natural proclivity to be philanthropic.” Kraemer reached out to colleagues at the biennial meeting of a unique group fostering collaborative work on water issues. The NSF-sponsored Consortium of Universities for the Advancement of Hydrologic Science (CUAHSI) includes more than 100 colleges, universities, and other institutions. Its major products include online data catalogs, open source software, and the biennial meeting, which is hosted by UCAR every other summer in Boulder. Dozens of researchers gave talks and presented posters in July at this year’s meeting. Keynote speakers included Roger Pielke Jr. (University of Colorado Boulder), Soroosh Sorooshian (University of California, Irvine), and Tom Dunne (University of California, Santa Barbara). “At the high latitudes and the low latitudes, we’re actually seeing increasing water tables,” says Jay Famiglietti, who directs the Hydrology & Climate Research Group at the University of California, Irvine. At the same time, he adds, “Most of the aquifers in midlatitudes are under huge stress.” (See “Reservoirs beneath our feet.”) Glaciers will also feel the pinch of a warming climate, although there are many questions about how quickly an increase in glacial melt might segue into eventual depletion for the millions who rely on glaciers as a primary or supplemental water source. (See “Who needs glaciers?”) How will we manage? As water managers contemplate the future, they’re paying close attention to where efficiency and conservation can make the biggest gains. A new global outlook by the National Intelligence Council predicts that nearly half of humanity will live in water-stressed regions by 2030. Globally and nationally, agriculture gulps more water than any other part of society, making up roughly 80% of water consumption. A single farmer atop the Ogallala Aquifer of the High Plains may draw on as much water as a good-sized city. The ongoing global rise in meat eating is expected to put additional strain on water resources, since it typically takes more water to produce a calorie of meat versus one of grain. The energy sector accounts for an estimated 27% of nonagricultural U.S. water use, as noted in a 2010 Harvard report. Aside from the large amounts of water required to grow corn for ethanol, water is pumped through coal plants and nuclear reactors to keep them cool. Much of that water returns to source streams, albeit at higher temperatures than before. Large amounts of water are also pumped into the ground to squeeze out oil and natural gas, through the technique known as fracking (hydraulic fracturing). This year’s drought is already putting a crimp on the hydrocarbon boom in some U.S. states. For the public, water utilities are the most familiar part of the supply chain, especially when customers are asked or required to restrict water use during dry periods. Through his work with a variety of clients from Florida to California, NCAR’s Yates has seen what happens when finite supplies go head to head with development pressures. “It’s hotly political. People want to build,” he says. However, he believes the intensity of recent droughts, together with rising demand, is starting to engender more caution: “I think the utilities are questioning their assumptions.” David Yates (©UCAR. Photo by Carlye Calvin.) A utility-based alliance is now helping bring water providers into the loop on climate research. (See ”Keeping the tap flowing.”) Yates and NCAR economist Kathleen Miller published a guide (see PDF) to help drinking water utilities anticipate how climate change might affect supply and demand. And Yates collaborated with Denver Water and consulting firm Riverside Technology on a report released in March by the Water Research Foundation. It examines the potential impacts of climate change on water supplies in Colorado’s populous Front Range region, using two different hydrology models. The NCAR-based Colorado Headwaters project is also producing new detail on how precipitation may evolve in the high mountains that feed the Colorado River. (See ”Three state of water.”) Colorado offers a useful window into the complexities of water projections, according to Brad Udall. He directs the Western Water Assessment, one of NOAA’s seven Regional Integrated Science and Assessment groups. “We get affected by weather from all points on the compass,” says Udall. “We’ve got these big mountains and summer monsoonal flow. All of these things are difficult to resolve in our current models.” Stir in climate change, and this detailed portrait morphs into a motion picture. “When a lot of people talk about climate change adaptation, they say, Give me a target and I’ll plan for it. That doesn’t appreciate the fact that the target is going to move throughout the 21st century.” As a rule, says Udall, “We don’t deal very well with moving targets.” Kevin Trenberth (©UCAR. Photo by Carlye Calvin.) A global eye on energy and water cycles The world’s most comprehensive program to outline the flow of heat and moisture through Earth’s atmosphere is heading in new directions. Formerly the Global Energy and Water Cycle Experiment, GEWEX is now Global Energy and Water Exchanges. Adopted in July, the new name reflects the broadening nature of the group’s work. “We recognized that the old name was obsolete—we are no longer an experiment,” says NCAR’s Kevin Trenberth, who chairs the GEWEX scientific steering group. GEWEX is in its 25th year as part of the World Climate Research Programme, with an international project office supported by NASA and located in Silver Spring, MD. Drawing on support from a variety of participating nations, GEWEX fosters collaborative field projects, workshops, dataset development and assessment, and other activities to bolster research on water and energy cycles, with the ultimate goal of reproducing and predicting global hydrologic processes and their effects. As part of an overall revamp of the parent program toward research that supports climate services, GEWEX has adopted a new set of seven imperatives, as well as four grand science questions: How can we better understand and predict precipitation variability and changes?  How do changes in land surface and hydrology influence past and future changes in water availability and security? How does a warming world affect climate extremes, especially droughts, floods, and heat waves, and how do land area processes, in particular, contribute?  How can understanding of the effects and uncertainties of water and energy exchanges in the current and changing climate be improved and conveyed?  

Three states of water

August 13, 2012 | From ocean to ocean, the relationships between individual states and their water supplies are changing. Climate scientists have projected serious regional changes over the next 50 years, but many states are already having to make tough decisions regarding their water use and their interaction with water. Among them are Colorado, Louisiana, and Oklahoma. NCAR scientists are involved in collaborative projects in all three states to evaluate the long-term effects of today’s decisions. Along the Colorado From its high-altitude origins just west of the Continental Divide in the Colorado Rockies, the Colorado River flows onward, providing water for cities and farms throughout much of the southwestern United States. (Photo by Bonnie Carol.) Recent statewide fires have moved Colorado residents to ask hard questions about the future of water and drought in the state. Models project that the warming atmosphere will change the character of winter storms in the Rocky Mountains, affecting residents and farmers across the Southwest who rely on the storms as their primary water source. Snowmelt from the high peaks of the Rockies provides more than 80 percent of the water flowing downstream to major cities, including Phoenix and Las Vegas. To better understand how winter storms will be affected by changes in climate, scientists at NCAR’s Research Applications Laboratory are working to perfect the modeling of precipitation, snowpack, snowmelt, runoff, and other variables in the high-altitude basins where the Colorado River begins its southwestward trek to the Pacific. NCAR's Roy Rasmussen heads the interdisciplinary team behind the Colorado Headwaters Project. (© UCAR. Photo by Carlye Calvin.) Dubbed the Colorado Headwaters Project, this team of 15 people led by Roy Rasmussen is made up of atmospheric and social scientists and engineers. It also collaborates with researchers at the University of Colorado Boulder, the University of Washington, and the University of Texas at Austin. The goal is to better understand how the complex terrain of the Rockies affects rain and snow on the small scale, and to incorporate that knowledge into larger-scale projections from climate models going decades into the future. The team used the advanced research version of the Weather Research and Forecasting model (ARW), which reproduced snowfall and other weather variables for four winters from the last decade with high accuracy at points separated by as little as 5 kilometers (about 3 miles). They also drew on results from the NCAR-based Community Climate System Model (which is supported by NSF and the U.S. Department of Energy). Those results indicated that the region’s climate would see a 3.6ºF (2ºC) increase in temperature and a 15% increase in precipitation over recent conditions by 2045–55 if global emissions of greenhouse gases continue to increase at a moderate pace. The group then used the CESM estimates with ARW to determine what would happen on a finer scale. Colorado’s famed terrain produces wide variations in rain and snow across small areas. To better reproduce these patterns in weather and climate projections, the Colorado Headwaters effort is employing high-resolution models that depict major peaks, ridges, and valleys across the state. (Image courtesy Colorado Headwaters project.) The results showed that snowfall increased overall by 12% at midcentury compared to the past decade. However, the results varied by altitude: snowpack increased at the highest elevations and decreased at lower elevations. "Our results show islands of enhanced snow in the highest Colorado peaks, surrounded by areas with more rain and melting," says Rasmussen. Spring melt occurred three weeks earlier than today, and the snowline elevation increased by an average of 660 feet (200 meters). Shifts in runoff and evaporation were also projected. Future studies will consider changes in storm tracks. These findings suggest that different cities will be affected different ways. In states such as Arizona, the changes could mean severe drops in water access; in Colorado, the results suggest a shorter snow season and a snowpack that melts and evaporates more quickly, even with the potential for heavier snow at the highest elevations. David Gochis, an NCAR scientist who works on the project, puts things into perspective from a water-management point of view: “We will still face significant challenges in water management. There will be more evaporation and more pressure on water supplies, particularly in the summertime,” he adds. Coastal concerns At the northern end of Isle de Jean Charles, 30 families of the Biloxi-Chitimacha-Choctaw tribe hold on to land threatened by environmental and commercial pressures. Extending from the top right of the photo is Island Road, the only means of getting to the island from the mainland. (©UCAR. Photo by Monika Wnuk.) On the other side of the Continental Divide, waters from eastern Colorado and many other states flow into the mighty Mississippi, eventually spilling into its famed delta in far southeast Louisiana. Here, the rapidly changing coast tells a complex water story pertinent to coasts everywhere. Hurricanes Katrina and Rita brought attention to the delta’s vulnerability to natural forces, but the daily vulnerability of the coast to geologic and human activity is talked about less often. Natural buffers against storm surge have long been a function of barrier islands, healthy marshes, natural ridges adjacent to bayous, and cypress swamps. In combination with artificial levees, these landscape features have allowed humans to live and work in an otherwise flood-prone area. However, society has also jeopardized the ability of the landscape to repair itself. Land subsidence (sinking) coupled with a rise in sea level have exacerbated erosion and allowed destructive storm surges to penetrate the coast and move further inland. When humans are not affecting the landscape, then river deltas can work to both erode and replenish barrier islands in a cyclic fashion. However, levees built to divert sediments away from Louisiana’s coast haven’t allowed for this cycle to unfold. Moreover, decades of oil drilling have left open pipelines underwater that encourage the flow of salt water into delicate wetland ecosystems. Unaccustomed to saltwater, entire cypress swamps decay along the coast, further contributing to flooding and erosion. NCAR’s SOARS program (Significant Opportunities in Atmospheric Research and Science) sent two students to Louisiana this summer to investigate this multifaceted water issue. See the sidebar at the bottom to dive deeper into the specifics of their community-based research. Drought in a boom-and-bust water regime Only months after heavy winter rains erased a severe drought, Oklahoma returned to record heat and bone-dry conditions in the summer of 2012, paving the way for destructive wildland fires. A fire just east of Norman on August 3 spawned this pyrocumulus cloud, photographed from the roof of the National Weather Center. (Photo courtesy James LaDue, NOAA.) Where Louisiana looks to mitigate the effects of too much water, Oklahoma struggles to make sense of year-to-year variability in precipitation. “There is nothing steady about rain in Oklahoma,” says Jeffrey Basara, director of research at the Oklahoma Climatological Survey. Basara recalls periods of significant drought in 2000, 2006, 2011, and 2012 and how sharply they contrasted with extreme rainfall events like the record-breaking flash flood in Oklahoma City in 2010. Such variability on short time scales calls attention to future water sustainability in the state.  In Oklahoma, aquifers provide most of the water distributed to homes and businesses. The Arbuckle Simpson Aquifer, located in the south-central part of the state, is the only source of water that supports the various streams, rivers, and lakes in a 500-square-mile area, supplying a total of 39,000 users. Ownership and limits to use of the aquifer are now being disputed by a mix of parties, including landowners who wish to sell the water to neighboring states, a group of citizens concerned about preservation and sustainability of Oklahoma’s water supply, and members of the Chickasaw Nation who claim original rights to the source. Since 2003 the aquifer has been studied more intensively than any other in the state. Shown here in light brown, the Arbuckle-Simpson Aquifer is located in south-central Oklahoma. (Map courtesy U.S. Geological Survey.) Scientists in NCAR’s Earth System Laboratory (NESL) are using an interdisciplinary approach to chart how people value water and perceive drought risk in south-central Oklahoma and whether this lines up with climate projections for future water availability. Environmental anthropologist Heather Lazrus is teaming with climatologist Debasish PaiMazumder and ecosystem scientist Erin Towler on the project. NCAR's Heather Lazrus brings an anthropological perspective to an interdisciplinary study of water use in Oklahoma. (©UCAR. Photo by Carlye Calvin.) Based on a foundation of anthropological theory, Lazrus is conducting and analyzing interviews in hopes of illuminating the cultural mechanisms through which people understand water-related risk. PaiMazumder is using NCAR’s Nested Regional Climate Model to develop plausible drought scenarios in Oklahoma’s current and future climates through an exploration of drought impact indices (mainly precipitation, temperature, and soil moisture). And Towler is analyzing stream flow patterns in wet and dry years to understand the impact of drought. Using Lazrus’s findings on how people view water availability and drought risk, PaiMazumder will develop a new index for assessing the damage caused by droughts. The results will be made available to water planners and the public. Also, Towler will identify impacts to drinking water, fishing, and other ecosystem components that rely on water availability. “Our hope is to communicate the potential of drought in a way that parallels how people understand it,” says Lazrus. Monika Wnuk, a recent graduate of the University of Chicago, was an intern with NCAR & UCAR Communications in the summer of 2012. SOARS protégés lead research in the bayou A human issue accompanies the changes in land and water use in coastal Louisiana, where economically vulnerable populations live For her 2012 research as a UCAR SOARS protégé, Sandra Maina (Florida International University) worked with residents of far southeast Louisiana and conceptualized a smartphone application to depict the science and the human stories behind their sinking landscape. (©UCAR. Photo by Monika Wnuk.) on land that is in immediate danger. Among these groups is the Biloxi-Chitimacha-Choctaw Native American tribe residing on the island of Isle de Jean Charles. Forced by westward expansion in the 1800s onto the southernmost part of the Mississippi Delta, this tribe struggles to hold onto the land that has long sustained it. Out of a population of 80 families a decade ago, the remaining 30 families of Native American descent live on a two-mile strip of land on either side of one road, surrounded by land that has become too soggy for use. Residents can only point to where their family’s cow pastures, forests, and cemeteries used to be. A four-foot dirt levee separates their homes from the Gulf of Mexico. Residents drive almost daily to the mainland on a low-lying road that tends to flood. But relocation would be expensive, and there are other factors keeping the remaining families in place. For example, the region is considered a fishing paradise, and tribal members are constantly at odds with fishermen who set up camps on the island. Through UCAR’s SOARS program (Significant Opportunities in Atmospheric Research and Science), Sandra Maina, a graduate student in environmental studies at Florida International University, and Frances Roberts-Gregory, a senior in environmental science and anthropology at Spelman College, spent the summer of 2012 conducting interdisciplinary research in this vulnerable community. Maina and Roberts-Gregory were introduced to local issues by their community mentor, Kristina Peterson, a research associate at the University of New Orleans Center for Hazards Assessment, Response and Technology. Peterson is deeply invested in the community, serving as a pastor at the local Bayou Blue Presbyterian Church and as an activist for the region at conferences across the nation. Following the guidelines of participatory action research, Maina and Roberts-Gregory asked members of the community to express their needs, then designed their projects accordingly. Maina met with community members on the five most vulnerable strips of land along the coast—Chauvin, Dulac, Dularge, Montegut, and Pointe au Chien—in order to identify points of cultural interest that are at risk of flooding and erosion. Following her summer of fieldwork, she hopes to direct the creation of a smartphone application that would map these places and include a history of each one, along with a video message from a community member. The app would also keep users updated on ongoing restoration projects in the area. Even some homes and business that were built on stilts to accommodate flooding are now difficult to access at any time. (©UCAR. Photo by Monika Wnuk.) “Lots of big organizations want to exclude the community,” says Maina. “This smartphone app seeks to include and empower it.” Roberts-Gregory applied tools from ethnobotany and anthropology to determine which culturally significant plants are threatened by ecosystem changes. Her procedure started with documents from the 1930s that details curatives used by Native Americans in the area, supplemented with conversations with community members who work with the same plants. Roberts-Gregory describes her experience with participatory action research as “just as complex as the water situation in Louisiana.” Every week brought new conversations, focus groups, content analysis, and new angles to the issues at hand. Although the process took time, she sees community input as essential to community-relevant results. Both students hope that future scientists continue community-based interdisciplinary projects in the region. From what they’ve seen, residents know the issues and are eager to continue the conversation—and move into action.


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