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Final Report: Regional Hydrologic Vulnerability and Adaptation to Climate An Integrated Assessment of the Susquehanna River Basin
EPA Grant Number: R824807Title: Regional Hydrologic Vulnerability and Adaptation to Climate An Integrated Assessment of the Susquehanna River Basin
Investigators: Yarnal, Brent , Crane, Robert , Fisher, Ann , Lynch, James
Institution: Pennsylvania State University - Main Campus
EPA Project Officer: Winner, Darrell
Project Period: November 1, 1995 through October 1, 1998
Project Amount: $460,000
RFA: Regional Hydrologic Vulnerability to Global Climate Change (1995)
Research Category: Global Climate Change , Ecological Indicators/Assessment/Restoration
Description:
Objective:How vulnerable is society to future climate-induced variations in hydrology and water resources? What can the impacts of previous climate extremes on hydrology and water resources teach us about present and future vulnerability? What is the potential for our water supply systems to adapt to future climate extremes? This project attempted to answer these questions by studying the impact of climate variation and change on the freshwater resources of the Susquehanna River Basin (SRB), with special emphasis on community water systems. Summary/Accomplishments (Outputs/Outcomes):
The Susquehanna River Basin, the largest U.S. watershed east of the Appalachian Mountains, has 1.5 million households (3.5 million people). Approximately 0.5 million rural households (35 percent of all households in the basin) rely on privately owned wells for their primary water supply. Of the remaining households, about 1.0 million (65 percent) are on a community water system (CWS).
Weather and climate extremes affect the safety and water resources of this population. Isolated flashfloods are common, especially in the mountainous upstream portions of the basin. Massive, basin-wide floods also have been experienced many times, including the major floods of March 1936, June 1972, and January 1996. Despite this tendency to flood, and despite ever-increasing wetness throughout the 20th century, the SRB is no stranger to drought. In the last century, serious droughts occurred in every decade but the 1970s. In the 1990s alone, the Governor declared drought emergencies in 1991?1992, 1995, and 1998?1999.
Four global climate models (GCMs) were used to generate climate scenarios for the 21st century SRB and then to relate those scenarios to basin hydrology. The climate models include the British Hadley Centre and the Canadian Climate Center transient GCMs, and two versions of the GENESIS equilibrium GCM with a doubling of atmospheric CO2. Although the models do not agree on the season of peak precipitation, three project a warmer and much wetter SRB in the future, while the fourth projects a much warmer and marginally wetter region. Model projections also demonstrate that future streamflow, groundwater level, and water quality will change significantly in association with climate change. Although it is clear that climate change will influence future hydrology and water resources, considerable uncertainty over the exact nature of that influence will continue until climate model scenarios improve and converge.
The modeling research suggests that although it is not yet feasible to determine the intensity and timing of future floods and droughts, it is possible to assess potential impacts and vulnerability by studying past floods and droughts. It is especially useful to investigate the impacts of floods and droughts associated with weather and climate scenarios that have a high likelihood of occurring in the future, or that will be particularly devastating if they do occur. Such scenarios correspond to the experience of the 1990s in the SRB. Thus, the research used the floods and droughts of the 1990s to provide insights to potential impacts and vulnerabilities associated with climate change.
The floods of 1996 in the SRB were unprecedented in their frequency, requiring six separate presidential disaster declarations for recovery. The floods were part of a highly unusual wet year in which, when averaged over the basin, the total precipitation was 44 percent more than the long-term average. It was easily the wettest year experienced in more than a century of recordkeeping and was consistent with the GCM scenarios of the 21st century. Case studies were conducted for the rain-on-snow flood of January, the flashfloods of summer, and the flashfloods resulting from Hurricane Fran. The January flood demonstrated that large populations are vulnerable to rain-on-snow floods, including people who live considerable distances from floodplains. Future socioeconomic costs resulting from rain-on-snow floods could be very large, because global warming is likely to increase the frequency of such events. GCM scenarios also suggest that climate change could result in more severe spring and summer thunderstorms, extreme rainfall events in the basin, and consequently, more flashflooding. Although the severe thunderstorms and flashfloods of summer 1996 affected thousands, disaster declarations were only forthcoming in two cases. For many victims, because of the isolated and scattered nature of these thunderstorms and because flooding often occurred outside of floodplains, damages were not covered by insurance or by other social safety nets. Flashflooding also was the main impact of Hurricane Fran, which caused serious damage in 15 SRB counties. Of these, nine Pennsylvania counties did not receive public assistance because they were not declared federal disaster areas; in these cases, only individuals and businesses carrying federal flood insurance before the storm were qualified to receive compensation. Even when a county received a disaster declaration, funds were uncertain, slow, and significantly less than the actual loss.
The GCM climate scenarios suggest that increased flooding may be a bigger problem than drought in the 21st century. Nevertheless, when natural climate variation reduces the amount of precipitation in the future, it is likely that the higher temperatures associated with climate change will induce more frequent drought, even in a wetter SRB. The three droughts of the 1990s, all embedded in a period of rising average precipitation, give testimony to this scenario.
Consequently, case studies examined the sensitivity of CWS to all climate variation, including floods and droughts. Two case studies looked at the effects that changes in regulation??specifically regulations stemming from the Safe Drinking Water Act (SDWA) Amendments of 1986 and 1996??had on the vulnerability of CWS to climate variation. These studies suggest that the SDWA has had a significant impact on the operation of water systems and has had the side benefit of reducing their vulnerability to weather and climate. Another case study demonstrated that state policies, such as the Pennsylvania Drought Management Plan, have reduced impacts of weather and climate. Nonetheless, government action can increase CWS vulnerability. A case study of state-funded infrastructure improvements showed that smaller CWSs are less likely to apply for funding to improve water-system facilities. In addition, proportionately fewer small systems apply for and receive funding than do large systems. Thus, these funding practices appear to make small systems comparatively more vulnerable to weather and climate extremes.
To follow up and amplify the case studies, the project surveyed 506 CWS managers in the SRB. Four essential findings emerged from the survey. First, most CWS managers report serious problems from weather and climate events. Second, the vulnerability to weather and climate is determined more by type of system than by system size. CWSs that rely partly or wholly on surface water face more disruptions than do systems that rely on groundwater. Third, CWS managers are unsure about climate change. Few managers dismiss the issue; most think climate change could be a problem, but are unwilling to consider it in their planning activities until greater scientific certainty exists. Finally, experienced, full-time managers are more likely to consider future weather and climate scenarios in their planning. Inexperienced and part-time managers are less likely to do so.
In sum, many lessons can be learned from the project. The flood research shows that American society handles flood losses by insuring residents in floodplains and, when disaster strikes, by declaring federal disasters. Most people and businesses located outside of floodplains are not aware that they are at risk of flooding. Although this population is sometimes eligible for flood insurance, it is usually unaware of its eligibility. Unless these uninformed people purchase federal flood insurance or receive a presidential disaster declaration, they effectively have no protection. Ineligible people have no access to protection without a disaster declaration. Thus, in the face of increased floods in the 21st century, this research suggests that American society needs to rethink how it provides financial protection against floods.
Another major lesson is that government action can have unintended, secondary effects on vulnerability to weather and climate. The government can be a positive agent for reducing vulnerability to weather and climate and for adapting to climate change, but it also can hinder effective adaptation. The government should routinely assess the possible secondary effects of its action on vulnerability and adaptation to climate variation and change.
The water managers survey presents three separate lessons. The first lesson is that CWSs are less vulnerable to weather and climate extremes when their main supply comes from groundwater. The government should continue to promote and find ways to accelerate the conversion from surface to groundwater in CWS. The second lesson from the survey is that weather and climate information and the clear communication of that information is essential to resource managers. Because resource managers need concrete information on climate variation and change, research aimed at reducing scientific uncertainty about climate variation and change must continue and, perhaps, accelerate. Finally, at least for better planning concerning the impacts of weather and climate extremes on water supply, even small communities must strive to hire and retain experienced, professional resource managers.
Ultimately, these lessons suggest that the government at the federal, state, regional, and local levels should help communities and individuals develop ways to: (1) protect themselves financially against floods; (2) insure a secure water supply in the face of a varying and changing climate; and (3) afford and retain long-time resource managers. Even if present climate change scenarios are unrealistic, it is clear that society and its resource systems will continue to be sensitive to weather and climate extremes.
Journal Articles:No journal articles submitted with this report: View all 28 publications for this project
Supplemental Keywords:climate variation, climate change, climate hazards, floods, droughts, water resource management, water supply, drinking water, Pennsylvania, PA,
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Water, Air, Geographic Area, Scientific Discipline, RFA, Water & Watershed, climate change, Ecological Risk Assessment, Atmospheric Sciences, EPA Region, Hydrology, Watersheds, State, Global Climate Change, hydrologic models, socioeconomic indicators, Susquehanna River Basin, watershed, Pennsylvania, climatic models, Region 3, mountain water resources, economic models, environmental monitoring, integrated assessments, climate models, climate variability, PA
Relevant Websites:
http://www.essc.psu.edu/srbia
http://www.geog.psu.edu/gcimpacts
http://www.essc.psu.edu/cira
http://www.essc.psu.edu/ccimar
http://www.essc.psu.edu/mara/
Progress and Final Reports:
1998 Progress Report
Original Abstract