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<br />/'1' <br />I .~.. <br />}, <br /> <br />precipitation events may be out of phase with that observed, and precipitation spatial <br />distributions do not have the resolution needed for local-scale hydrologic models. <br />Limitations of the MM4 convective simulations may be resolved through nesting a <br />sophisticated local-scale, three-dimensional model. Case examples of convective <br />precipitation simulations using this anelastic primitive equation Clark model with <br />parameterized microphysics will be presented at the conference. <br /> <br />Introduction <br /> <br />This study is part of Reclamation's (U. S. Bureau of Reclamatioh) research in its <br />GCCRP (Global Climate Change Response Program), which i.ncludes a collaborative <br />effort described by Dennis (1991), Matthews et al. (1991), and Medina (1991). This <br />collaboration involves scientists from the NCAR (National Center for Atmospheric <br />Research) and the GS (Geological Survey). The GCCRP is designed to determine <br />the effects of climate change on water resources in selected western drainage basins. <br />Reclamation and GS are jointly examining the precipitation and hydrologic <br />characteristics of the Gunnison River Basin to determine streamflow properties and <br />reservoir management needs in present and future climates. This 'drainage basin is <br />typical of other headwaters for the Upper Colorado River and other major river <br />systems in the West. Therefore, to determine the effects of climate change on <br />precipitation, Reclamation is modeling the physical mechanisms that produce <br />preCipitation and thereby describe the spatial and temporal evolution of precipitation <br />from various types of winter and summer precipitation events. This paper briefly <br />outlines a nested modeling approach to examine precipitation over the Rocky <br />Mountains in Colorado and presents an assessment of a regional model's precipitation <br />simulations in complex terrain. The paper identifies the need for a nested <br />regional/local-scale modeling system to accurately simulate local-scale precipitation <br />processes over complex terrain. <br /> <br />Reclamation's GCCRP modeling approach involves two phases. Phase 1 <br />evaluates the nested regional/local-scale modeling method in current climate to <br />determine its capability to accurately simulate existing conditions in well-documented <br />cases. In phase 1, the regional model has been initialized by observed data sets and <br />run in a climate simulation mode for 40 months. As confidence in the large-scale, <br />general circulation model results improves, phase 2 will apply the nested modeling <br />approach to future climate simulations that include effects such as doubled C~. <br />These simulations will use a general circulation model, a regional model, and a local- <br />scale model. <br /> <br />In phase 2, the general circulation model will provide synoptic-scale information <br />that initializes the regional model, which will simulate the regional evolution of storm <br />structure. Then a local-scale model will use the regional analyses for its initial <br />conditions and simulate local-scale precipitation with high-resolution (dx= -5 to 10 <br />km) topography. This paper focuses on research in phase 1 - the validation of the <br />regional model and early stages of testing a sophisticated, local-scale, time-dependent <br />model. <br /> <br />') <br /> <br />~,f .,tthp",,, pt .,1 <br />