Spatial interpolation of daily precipitation based on modified ADW method for gauge-scarce mountainous regions: A case study in the Shiyang River Basin

Precipitation is among the major drivers in hydrological modeling, and spatial rainfall distribution is essential for understanding ecohydrological processes. Inaccurate rainfall spatial surface is the main source of model uncertainty, especially where rainfall gauges are sparse in mountainous areas and, where the spatial precipitation distribution is closely related to elevation. This study proposes a daily rainfall interpolation method based on the Angular Distance Weighting (ADW) method considering the precipitation-elevation relationship and topographic effects derived from observed data. Furthermore, the method is used to generate daily rainfall in the Shiyang River basin from 1984 to 2012. Cross-validation results indicate that this method is rational, where the annual mean relative errors (MRE) are less than 30% at the majority of the stations. The rationality of the interpolated precipitation data at high altitude regions, where limited rainfall gauges exist, is also evaluated using a comparison of the observed and simulated runoff modeled by the Soil & Water Assessment Tool (SWAT). The SWAT model with interpolated rainfall could generate better-simulated discharges than that with observed rainfall data. The results demonstrate that the proposed method could provide an accurate spatial distribution of daily precipitation, which can sufficiently drive the hydrological model.