Physically Based Adjustment Factors for Precipitation Estimation in a Large Arid Mountainous Watershed, Northwest China

Abstract

This study is the first to investigate and improve a quasi–physically based model, MicroMet, by fitting its adjustment factor (χ) for a large data-scarce mountainous watershed in an arid area in Northwest China. The derived factors for both the whole study area (Derived Factor I) and different elevation classes (Derived Factor II) were determined and compared with the original factor in MicroMet for precipitation estimates, with a training period from 1990 to 2010 and a validation period from 2011 to 2013. Results show that the original factor in MicroMet is more suitable for estimating high precipitation over low-elevation areas (below 2,000 m above sea level), but it is not suitable in high mountainous areas. Both Derived Factors I and II can improve the performance of precipitation estimates, and more reliable adjustment factors could be obtained with more in situ observations. The Barnes objective analysis scheme used in MicroMet is more suitable for interpolating large precipitation events with small variability in humid areas; it requires adjustments for applications in arid areas. Although determined from limited observations in the study area, Derived Factor II performed better than Derived Factor I in winter, indicating that the derived factor for the elevation classes is more suitable for estimating extremely low precipitation with greater variability in data-scarce, high-elevation mountainous watersheds in arid areas.