摘要
The headwaters of the Rio Grande are located in the San Juan Mountains of southwestern Colorado and the upper portions of the river are fed primarily by snowmelt from winter storms. In contrast, the lower portions of the river accumulate runoff from thunderstorms of the summer monsoon season. Thus, the waters of the Rio Grande are strongly influenced by regional climate and could be vulnerable to climate change. In order to study water resources in the Rio Grande Basin and how they may be affected by changes in regional climate, a modeling system, which relies on the use of coupled atmospheric, runoff, and ground water models, is being developed. Preliminary work on the project has focused on winter precipitation simulations of the upper Rio Grande Basin and evaluation of the suitability of the atmospheric model for simulating regional climate. This paper describes the spatial and temporal precipitation variability predicted by this model. To examine the temporal variability, results of simulations carried out with the Regional Atmospheric Modeling System (RAMS), at 20 km resolution, are presented for the month of January 1996, representing a dry extreme for the region, and January 1993, representing a recent wet extreme. Results are also presented of a case study with higher resolution (5 km) over the upper Rio Grande Basin to examine spatial variability of the snowpack within complex terrain. The simulation results are compared to observations of daily-accumulated precipitation in the region.The comparisons of model predicted precipitation indicate that the RAMS model can reproduce the interannual changes in precipitation patterns found in the western US. In the month of January 1996, both RAMS and observed precipitation are highest in the northern mountain ranges of the domain. Likewise, in the month of January 1993, both predicted and observed precipitation in the southern tier of states are dramatically higher. Results of the simulations with increased model grid resolution indicate a modest improvement of precipitation estimates with the finer grid resolution over the Rio Grande Basin.