Document Type


Publication Date

January 1990


Executive Summary: This report summarizes work conducted during the funding period (July 1 through September 30, 1990) of a Cooperative Agreement between the United States Forest Service (USFS) and the Utah Water Research Laboratory (UWRL), Utah State University. The purpose of the agreement is to develop a Western Mountain Climate Generator (MCLIGEN) similar in function to the existing Climate Generator (CLIGEN), which is part of the Water Erosion Prediction Project (WEPP) procedure. Also, we are developing a Western U.S. snowpack simulation model for inclusion in WEPP. In the Western U.S., few meteorological observations exist in high elevation areas where Forest Service properties are located. Therefore, a procedure for estimating climatological variables in mountainous areas is needed to apply WEPP in these regions. A physically-based approach, using an expanded and improved orographic precipitation model, is being utilized. It will use radiosonde data and also lightning data to simulate convective storms. Climatological sequences thus estimated at ungaged locations will be represented using stochastic models, similar to the approach used in the existing CLIGEN, and their parameters will be available to users through maps. By using these stochastic models, WEPP users can synthesize climate sequences for input to WEPP. During the reporting period we have implemented the Rhea orographic precipitation model and begun preliminary model testing in two regions. Also, we have begun formulation of model modifications for handling convective events. Various snowpack and meteorological data sets have been acquired and others have been ordered. Some of these have been applied in initial applications of several snowpack models which habe been recoded in a modular form. Work has commenced on the statistical analysis of western climate sequences, including the preliminary assessment of the alternative stochastic model structures. Additional review of literature has been commenced for establishing design storms and design hydrographs for events of various return periods in mountainous regions. Accomplishments are summarized in three parts: 1) climatological process models, 2) snowpack simulation models, and 3) stoachstic models of climatological variables and parameter regionalization. A chapter of the report is devoted to each of these three parts.