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Final Report: The Influence of Global Climate Change on Mountain Water Resources
EPA Grant Number: R824803Title: The Influence of Global Climate Change on Mountain Water Resources
Investigators: Leung, L Ruby , Ghan, Steven J. , Neilson, Ronald P. , Waichler, Scott , Wigmosta, Mark
Institution: Battelle Memorial Institute, Pacific Northwest Division
EPA Project Officer: Winner, Darrell
Project Period: October 1, 1995 through September 1, 1998
Project Amount: $500,000
RFA: Regional Hydrologic Vulnerability to Global Climate Change (1995)
Research Category: Global Climate Change , Ecological Indicators/Assessment/Restoration
Description:
Objective:The goal of this project is to estimate the regional vulnerability of hydrologic systems to global climate change by using a case study of two mountain watersheds in the Pacific Northwest. Summary/Accomplishments (Outputs/Outcomes):
One of the more serious potential consequences of a greenhouse warming is a change in the phase of wintertime precipitation in temperate regions. Even if the amount of precipitation does not change, the expected higher proportion of precipitation falling as rain rather than snow in a warmer climate has serious implications for management of water resources. Predicting the changes in water resources under climate change has been very challenging because of uncertainties and the lack of spatial specificity in the climate predictions. Global climate models (GCMs), which are commonly used to provide climate projections, do not adequately resolve climate processes at the spatial scales required to assess water resources impacts, especially over the topographically diverse western United States.
This project specifically addresses the spatial specificity issue. Leung and Ghan at the Pacific Northwest National Laboratory have developed a regional climate model (PNNL-RCM)for downscaling GCM simulations to spatial resolution of 10 km or less. Their RCM features a novel approach to represent the influence of topography on temperature and precipitation using a subgrid parameterization which divides a model grid cell into a number of surface elevation classes. Their regional climate simulations can be disaggregated to provide high spatial resolution climate information for driving hydrology and ecosystem models at the watershed scale. This method is especially useful for simulating the hydrologic and ecologic conditions of mountain watersheds in the western United States.
A numerical experiment was designed to use this modeling approach to estimate the sensitivity of water resources to climate change in the Pacific Northwest. The modeling system consists of a regional climate model (PNNL-RCM), a distributed hydrology model (DHSVM), and a vegetation model (MAPSS-BGC). The latter is a newly developed dynamic vegetation model based on the biogeography model, MAPSS, and a biogeochemistry model, Biome-BGC. These models have been significantly refined to improve the physical representation and computational efficiency for this study. The RCM was used to produce two sets of climate conditions: a "control simulation" that corresponds to the present day climate, and a "2xCO-2 simulation" that corresponds to the projected climate when atmospheric CO-2 concentration doubles the present value of 340 ppmv. According to the Business-As-Usual CO-2 emission scenario discussed in the Intergovernmental Panel on Climate Change (IPCC) report, atmospheric CO-2 concentration will reach 680 ppm in the 2080s. In order to produce these simulations, a GCM was used to provide the large scale circulation necessary for driving the RCM. We selected the National Center for Atmospheric Research (NCAR) Community Climate Model (CCM3) because it produces reasonable simulations of the observed large scale conditions over the Pacific Northwest.
Our regional climate simulation results indicate that at 2xCO-2 there is an
average warming of about 2°C, and annual precipitation generally increases
over the Pacific Northwest and decreases over California. The combined effects
of surface temperature and precipitation changes are such that snowpack is reduced
(Figure 1), causing large changes in the seasonal runoff. In coastal mountains
such as the Cascades, snowpack is reduced by about 70% and the average snowline
moves up by about 1000 feet under the greenhouse warming conditions.
Figure 1. Mean annual snowpack at 2xCO-2 shown as percentages of the control.
Both the control and 2xCO-2 RCM simulations were used to drive DHSVM at the American River watershed on the east side of the Cascades, and the Middle Fork Flathead watershed on the Northern Rockies to estimate the impacts of greenhouse warming on surface hydrology. These two watersheds were selected to contrast the hydrologic response over coastal and continental mountains. Figure 2 shows the mean hydrographs simulated by DHSVM for the present and 2xCO-2 conditions for the two watersheds. The change in the hydrologic conditions is rather drastic over the American River. Because of the warmer temperature, the basin mean snowpack is reduced by about 60% and is completely melted about two months earlier in the 2xCO-2 simulation. There is a change in both the annual total as well as the timing of streamflow. The November winter peak under 2xCO-2 is more than doubled that of the control simulation. This is a result of the higher precipitation and warmer temperature which causes a higher percentage of precipitation to fall in the form of rain rather than snow. This causes a more immediate contribution to the runoff. Because of the reduced snow accumulation and early snowmelt, streamflow during the warm season under 2xCO-2 is significantly reduced. The change in the seasonal pattern of streamflow suggests a higher likelihood of wintertime flooding and reduced water supply in the summer under the greenhouse warming scenario.
Figure 2. The simulated streamflow at (a) the American River and (b) Middle Fork Flathead under the control and 2xCO-2 climate conditions.
Over the Middle Fork Flathead, the difference between the two scenarios is much less drastic than the American River. For example, the basin mean snowpack is only reduced by 18% and there is no change in the timing of the peak streamflow. However, consistent with the warmer temperature under 2xCO-2, streamflow during earlier winter is increased while that during summer is reduced.
The American River is a tributary near the headwater of the Yakima River where human and ecological demand for water already exceeds the stream's supply. A change in the seasonal pattern of streamflow can tighten the existing conflicts for achieving the objectives of flood control, irrigation water supply, and fish protection. Climate change is an important factor to be considered when managing water resources under the future demand and supply conditions. In a follow up study, we will extend our analysis to an integrated assessment of climate change impacts on water resources, agricultural production, and fishery in the Yakima River basin. Water resources management models will be used with the streamflow predictions for the present and future climate to evaluate the differences in system performance for a variety of policies to reflect the adaptability of the system operation.
To study the sensitivity of ecosystems to climate change, the MAPSS-BGC model has been fully hybridized with DHSVM to produce a Distributed Hydrology Biogeochemistry model, DHB, at the watershed scale. Differing and redundant modules and input data requirements of the models have been reconciled. This new modeling tool will be very useful for studying the impacts of climate and land use change on the ecosystem. The model has been tested on idealized watersheds and is currently being refined for more detailed studies. As a first estimate of climate change impacts on ecosystem, we used only the MAPSS model to study equilibrium vegetation changes. Accounting for the direct effects of CO-2 on water-use efficiency and indirect effects of temperature and precipitation changes on plants, the MAPSS simulations show that at 2xCO-2 there will be an expansion of forest in the Northwest and that the LAI will generally increase by 10 to 50 percent because of the wetter winter condition. These changes in vegetation can have an impact on water resources that has not been accounted for in the hydrologic simulations described above. To determine this impact, we repeated the two DHSVM simulations using present and future climate AND vegetation conditions. Results show that the 60 percent increase in LAI over the American River under 2xCO-2 has two major effects. First annual ET is increased by 24 percent and annual discharge is decreased likewise. Second increased LAI provides greater shading of the snowpack and causes delay in spring runoff. The combined effects of increased ET and delayed and slightly reduced snow melt cause an additional 30 percent reduction in the spring runoff peak at 2xCO-2. This suggests that vegetation changes should be considered when estimating climate change impacts on water resources.
Results from our study have been reported in six peer-reviewed journal papers, the Intergovernmental Panel on Climate Change Third Assessment Report, the Pacific Northwest Regional Report for the USGCRP National Assessment, and a special issue of the Journal of American Water Resources Association contributed to the Water Sectoral Report of the National Assessment. Furthermore, climate change impacts estimated by our study for the Pacific Northwest have been reported to the general public by Popular Science, Wall Street Journal - NW Edition, NW Public Radio, and numerous major newspapers such as the Seattle Post Intelligencer, Oregonian, Spokesman Review in the Northwest. The P.I. (Leung) was invited to give a presentation at a Washington State Senate Hearing (3/99), a briefing to the Mayor of Seattle and city council (4/99), and the executive team of EPA Region 10 (5/99) on the issues of climate change in the Pacific Northwest. On November 1999, she also joined scientists of the University of Washington to give a presentation at a public meeting in Pasco, WA, (one of 7 public meetings in the Northwest) to discuss findings in the National Assessment Regional Report.
Journal Articles on this Report: 5 Displayed | Download in RIS Format
| Other project views: | All 17 publications | 7 publications in selected types | All 5 journal articles |
| Type | Citation | ||
|---|---|---|---|
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Cole CA, Brooks RP. A comparison of the hydrologic characteristics of natural and created mainstem floodplain wetlands in Pennsylvania. Ecological Engineering, February 2000;14(3):221-231. |
R824803 (1998) R824803 (Final) R824905 (1999) R824905 (Final) R826110 (Final) |
not available |
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Leung, L.R., M.S. Wigmosta, S.J. Ghan, D.J. Epstein, and L.W. Vail, 1996: Application of a subgrid orographic precipitation/surface hydrology scheme to a mountain watershed. Journal of Geophysical Research-Atmospheres 1996;101(D8):12803-12817. |
R824803 (1998) R824803 (Final) |
not available |
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Leung, L.R., and S.J. Ghan, 1998b: Pacific Northwest climate sensitivity simulated by a regional climate model driven by a GCM. Part I: Control simulations. Journal of Climate. |
R824803 (1998) R824803 (Final) |
not available |
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Leung LR, Ghan SJ. Parameterizing subgrid orographic precipitation and surface cover in climate model. Monthly Weather Review 1998;126(12):3271-3232. |
R824803 (1998) R824803 (Final) |
not available |
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Leung LR, Wigmosta MS. Potential climate change impacts on mountain watersheds in the Pacific Northwest. Journal of the American Water Resources Association 1999;35(6):1463-1471. |
R824803 (Final) |
not available |
climate change, greenhouse warming, climate modeling, regional climate model, distributed hydrology model, precipitation, snowpack, streamflow, water resources, watersheds, Pacific Northwest. , Ecosystem Protection/Environmental Exposure & Risk, Air, Geographic Area, Scientific Discipline, RFA, Ecosystem/Assessment/Indicators, exploratory research environmental biology, climate change, Ecological Risk Assessment, Pacific Northwest, Ecological Indicators, Atmospheric Sciences, Ecological Effects - Human Health, EPA Region, Hydrology, Chemical Mixtures - Environmental Exposure & Risk, Ecological Effects - Environmental Exposure & Risk, Ecosystem Protection, CO2 concentrations, meteorology, carbon dioxide, Global Climate Change, hydrologic models, snowpack, surface water storage reservoir, climate change impact, groundwater, mountain water resources, vegetation models, environmental monitoring, watersheds, climate models, Region 8, ecological exposure, climate variability, Region 10, global change, Northern Rockies, global vegetation models, green house gas concentrations, regional hydrologic vulnerability, water resources, ecological effects, ecosystem models, global warming
Relevant Websites:
Regional Climate Model, Simulation Approach, Results:
http://www.pnl.gov/atmos_sciences/as_clim3.html#Mountain
Water 
Distributed Hydrology Model:
http://etd.pnl.gov:2080/watershed/
http://maximus.ce.washington.edu/~nijssen/docs/DHSVM/
Vegetation Models:
http://www.cgd.ucar.edu/vemap/abstracts/MAPSS.html
http://www.cgd.ucar.edu/vemap/abstracts/BGC.html
http://www.fsl.orst.edu/~waichler/frameset1.html
Snowpack Changes (A quicktime movie):
http://www.pnl.gov/atmos_sciences/snowmovie.html
Washington State Senate Hearing - Presentation:
http://www.pnl.gov/atmos_sciences/Lrl/index.html
Progress and Final Reports:
1998 Progress Report
Original Abstract