Simulations of precipitation over the upper Rio Grande Basin

This paper describes recent regional climate simulation predictions of precipitation that are part of a coupled atmospheric and hydrologic modeling system for simulating water resources within a river basin. The modeling system includes an atmospheric model that simulates regional climate and provides meteorological variables and precipitation to a surface hydrology model. The precipitation is then partitioned into evaporation, transpiration, soil water storage, surface runoff, and subsurface recharge. The runoff is collected within a simple river channel model and a subsurface model is linked to the land surface and river flow model components to simulate saturated and unsaturated flow and changes in aquifer levels. The result is a modeling system that addresses the multitude of physical processes and temporal and spatial scales necessary to calculate the current and future water resources within a river basin. We are currently focusing on linking the atmospheric model and the surface hydrology model and are simulating the upper Rio Grande Basin from its headwaters in the San Juan Mountains of southwestern Colorado to Cochiti Reservoir, near Albuquerque, New Mexico.

Our previous simulations of the regional climate of the upper Rio Grande Basin had employed 20 km horizontal grid spacing. However, a simulation of a single storm event suggested that increasing the horizontal resolution over the study area, from 20 km grid spacing to 5 km grid spacing, improved the model performance. This paper will focus on the precipitation fields produced with 5 km horizontal grid resolution over the Rio Grande basin that are being used in the calculations of runoff and soil moisture during the 1992-1993 water year. We will compare the predicted precipitation to the observed accumulated, water-equivalent precipitation as reported by Cooperative, SNOTEL, RAWS, and National Weather Service reporting stations for each month. We will also compare the results to the earlier simulation of January 1993 with the 20 km horizontal resolution to determine if the increased horizontal resolution gives consistently better predictions over the entire month. These results will be analyzed for different areas within the basin.