Water and water resources in many areas of the world are particularly sensitive to climate change. The water-limited regions such as the southwestern United States are a case in point. These regions are also experiencing rapid population growth and consequent competing demands for those limited water resources. As a result, water managers, western governors, and the general public are keenly interested in how the water cycle will change as the climate warms and what they might do to cope with such change. We see two topics as particularly important: (1) the potential that the mountain snowpack (the main water reservoir for the western United States) will decrease under climate change, changing the seasonal patterns of runoff and river flow; and (2) the threat of increasing drought under climate change and consequent societal vulnerability and response. To investigate these issues, we plan to
- Determine the principal controls (large-scale dynamics, moisture sources, orography, convective processes, etc.) on precipitation character (seasonality, frequency, intensity, and phase) in western North America and how these will respond to a changing climate
- Diagnose, in models and observations, the partitioning of precipitation among runoff, evapotranspiration, and groundwater recharge across western North America and define how this partitioning will change in response to climate change and landscape disturbance (e.g. forest dieback, shrubland succession, fire, urbanization)
- Improve model physics parameterizations (convection, microphysics, land surface, snow processes, planetary boundary layer) to enable credible climate model simulations of the water cycle over western North America
- Improve characterization of uncertainty in climate model simulations, through statistical and dynamical downscaling and multi-model ensemble processing (as in the North American Regional Climate Change Assessment Program, or NARCCAP) for the western North American water cycle
- Work with partners to examine the impact of climate change on groundwater storage (such as in the Ogallala Aquifer).
- Improve the characterization and parameterization of the impact of the water cycle on biogeochemical cycles through the BEACHON project
- Determine the leading drivers of societal vulnerability and adaptive capacity to changes in water availability in western North America and determine how state-of-the-art model scenarios can best inform decisions about water resources
- Develop modeling scenarios to explore how changes in population size and location, economic development, land use, and infrastructure impact water resource management, and how these processes are influenced by climate change
The resulting improvements to climate models and the inclusion of societal vulnerability and adaptation in model development and applications will benefit many other parts of the world, especially those with comparable vulnerabilities.