Department of Energy, Climate and Environmental Sciences Division
Winter storms and the Spring Transition over the western U.S.: Quantifying discrepancies between coarse and high-resolution simulations and observations
Arthur J. Miller, Dan Cayan, Dave Pierce, and Tim Barnett
Award: $450,000
Duration: 2009-2011
Project Summary.
Politicians and other decision makers in the western U.S. are, right now, using climate model projections of changes in western hydrology and the oceanic environment to develop policies on how water, agriculture, and fisheries should be managed in the future. Yet the structure, statistics, and regional hydrological impacts of winter storms and the realism and physical consistency of the spring transition have not been well characterized in the models. How well are these processes represented in CCSM, a model widely used in climate studies of the region? In particular, what aspects of the CCSM simulations can be taken as a sound basis for determining future policy, and what aspects are poorly represented yet have important policy implications, and so should be treated with caution? Establishing what CCSM does well and what needs to be improved is vital for ascribing confidence levels to predictions of climate change over the western U.S. and the adjacent Pacific Ocean.
The overall goal of the proposed research is to pinpoint what processes are inadequately modeled in low- and high-resolution CCSM simulations of current climate. We will achieve this by using sophisticated statistical techniques to study the dynamical balances, heat budgets, and hydrological cycles that are associated with modeled and observed winter storms and spring transition characteristics and structure over the western U.S., and their concomitant linkages to Pacific SST influence and regional oceanic response. The focus will be on the accuracy of simulation of regional-scale hydrologic variables.
We will first assess how realistically CCSM simulates winter storms and the springtime transition to warmer conditions over the western U.S., events that strongly influence the climate, economy, and society of the region. We then will create and document a ranked list of model deficiencies in simulating the distribution and structure of winter storms and the characteristics of the spring transition in the region, for the purposes of guiding development work aimed at improving the physical formulations in the models. We will use existing coarse (T42 atmosphere, 2/3o ocean) and high (0.25o atmosphere, 0.1o ocean) resolution coupled model runs, targeted AMIP-style runs, WRF simulations of selected storm events, and sophisticated statistical techniques to pinpoint the components of the model physical balances that contribute most to errors in simulating the regional climate. The outcomes of this work will be an improved understanding of the dynamical, thermodynamical and hydrological successes and deficiencies in CCSM.s ability to model storms and the spring transition in this region, and a prioritized list of model improvements most needed to better simulate this region. This work will lead to better climate scenario forecasts for use by policy makers and others, both immediately through a better understanding of the strengths and weaknesses of the current simulations, and longer-term by allowing model development to focus on the areas where improvement is most needed.