Comparison of Nested Models' Local-Scale Precipitation from a Three-Year Base Run and a Corresponding Doubled CO₂ Run

by Jonnie G. Medina, U.S. Dep of the Interior, Denver, United States,



Document Type: Proceeding Paper

Part of: Management of Irrigation and Drainage Systems: Integrated Perspectives

Abstract:

Comparisons were made of nested model simulated precipitation from a 3-yr base run and the corresponding doubled-CO₂ run for the Gunnison watershed of western Colorado. Output from the NCAR (National Center for Atmospheric Research) GCM (general circulation model), entitled CCM, was used to initialize the NCAR RSM (regional-scale model), known as MM4, that in turn produced output from which soundings were developed and used to initialize a simple LSPM (local-scale precipitation model). The LSPM was used to estimate grid-point precipitation at 10-km spacings. The modeling is a key component of the Bureau of Reclamation's (Reclamation) GCCRP (Global Climate Change Response Program) aimed at identifying potential impacts of global climate change on western river basins and developing strategies to deal with the impacts. Modeling with the LSPM was performed by Reclamation scientists, and GCM and RSM modeling were accomplished by NCAR scientists while improving the models. The GCM and RSM are complex three-dimensional, time-dependent models. The LSPM is a two-dimensional, steady-state model. Precipitation comparisons between the base and doubled-CO₂ runs were made using the average of 14 high-elevation estimates from the watershed. The (statistical) distributions of daily estimated precipitation were also compared. Results suggest the nested models are capable of producing plausible daily precipitation distributions in simulations of future climate.

Subject Headings: Scale models | Precipitation | Computer models | Simulation models | Watersheds | Statistics | Comparative studies | Colorado | United States

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