measurements and observations and more recently on the use of numerical models to simulate what is being observed and to predict what may happen in the future as conditions change. Choosing the most effective models to capture atmospheric and hydrological processes in very complex terrain was no simple matter. Researchers selected the Weather Research and Forecasting (WRF) model coupled with a distributed hydrological framework (WRF-Hydro) for their work. Running the model at very high resolution (4km), they have created a continuous eight-year simulation of possible climate scenarios for the mid-21st century. These “pseudo-climate change” scenarios have been analyzed to understand how the hydrologic cycle will change under a warmer climate. Preliminary results indicate that there will be increased winter precipitation in the Headwaters region in 2050. Annual runoff is expected to decrease, however, given increased evapotranspiration in a warmer climate.

Simulations in the Colorado Headwaters are being used to assess the impact of climate change in the Western U.S. using NCAR’s Nested Regional Climate Model at a 12km resolution. Results from these efforts are improving the WRF and WRF-Hydro models which are freely shared with the research and operational forecast communities. In addition, snow modeling advances are being used to improve the National Weather Service’s Community Hydrologic Prediction System to make more accurate seasonal drought predictions.

BackgroundDecision and policy makers are increasingly faced with the need to understand the impact of climate change on water and energy resources in the Western United States. With support from the National Science Foundation, the U.S. Bureau of Reclamation, the U.S. Army Corps of Engineers, and NOAA, NCAR scientists are working to understand fundamental hydrological processes under current and future climate conditions and to bring this state-of-the science understanding to bear on operational decision making and resource planning. This information, as well as new decision support technologies, will be increasingly important for state and local resource planning, wildland fire prevention and suppression, the agricultural and energy industries, forest and rangeland management, and agencies tasked with emergency response and public safety.

Western Snowpack PredictionMuch of the water the Western U.S. depends upon comes from the high mountains of Colorado. This area, known as the Colorado Headwaters, stores much of the region’s water in the form of snowpack. Water managers, as well as the general public, are well aware of snowpack measurements in western states’ river basins. Winter precipitation—how much it snows, when it snows, and where it snows—is closely watched. Equally important, though harder to measure and understand, is what happens to that snowpack when temperatures begin to warm in the spring. When does the snow begin to melt? How much goes into the ground versus into the air through evapotranspiration? Does runoff occur slowly over five months or quickly over three? These questions have always been difficult to answer, but adding the climate change wildcard to the equation makes them even harder and makes the need for credible answers more important.

In 2008 NCAR launched a new research program to assess the impact of climate change on winter precipitation, snowpack and runoff processes in the Colorado Headwaters. Understanding these processes has long depended on

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Fractional change in annual runoff between 2001-08 and 2045-54 in western water basins based on a high-resolution WRF model

simulation driven by average future (2045-54) temperature and moisture conditions of the NCAR Community Climate Model

(CCSM). Warm colors indicate decreased runoff.

Western Water and Energy

National Center for Atmospheric Research

Water and Energy Decision MakingIn addition to conducting research, NCAR scientists and engineers develop tools and technologies to improve forecasts and inform planning and management decisions. One of the most powerful decision support technologies NCAR brings to water resource planning and management is the Water Evaluation and Planning (WEAP) model, developed in collaboration with the Stockholm Environment Institute (SEI). WEAP is a sophisticated, yet user-friendly, tool that couples physical hydrology with relevant water management parameters, set by the user, to create scenarios to explore potential consequences of climate change on water management decisions. WEAP is currently used by several thousand water resource managers in the U.S. and in 170 countries around the world. Use by utility managers in California, Colorado and Florida has demonstrated the model’s ability to capture regional differences in an area’s dominant hydrologic processes. The model has also been proven effective in describing a variety of disparate water-management problems, including costs of capital investment, water law, state and local regulations, and ecosystem valuation, to more fully encompass the many non-hydrological variables managers must consider.

Policy and decision makers, particularly in the Western U.S., have long understood the interconnections between water and energy production and use. Water is needed throughout the energy production system for fuel extraction and processing, power plant cooling, hydroelectric production, etc., and energy is essential for pumping, treating and distributing water. Efforts to address climate change have heightened awareness of these linkeages—the “water-energy nexus”—and of the need to integrate water and energy planning and management. Attention is increasingly focused on water scarcity as conflicts emerge and are likely to escalate over

competing water demands for energy production, municipal use, agricultural irrigation, and ecosystem protection. At the same time, energy demand from the water sector—especially for irrigation but also for desalination, water transfers, and water and sewage treatment—has emerged as a serious concern.

While recognition of water-energy nexus issues has grown, tools that can capture the complexity of the relationships between the resources have only recently been developed. Scientists from SEI and NCAR have taken the WEAP model, described above, and coupled it with another model, the Long-range Energy Alternatives Planning (LEAP) system, to create a powerful new integrated planning and decision making tool. WEAP and LEAP can now exchange key model parameters and results and represent evolving conditions in both water and energy systems.

Using WEAP and LEAP together, planners can now explore how individual water or energy management choices ripple through both systems, understanding tradeoffs that might not be apparent when looking at either system alone. They can then evaluate outcomes against their policy goals and priorities, assess costs and benefits, and tweak decision parameters or make other choices to produce more desirable outcomes.

For More Information, Contact:Roy Rasmussen 303-497-8430 rasmus@ucar.edu David Yates 303-497-8394 yates@ucar.edu NCAR, Research Applications LaboratoryPO Box 3000 Boulder CO 80307-3000www.ral.ucar.edu

The Integrated WEAP and LEAP tools, showing the linking window (center),where common modeling areas, scenarios, periods of analysis, and timesteps are matched.