Precipitation change assessment over upper Bagmati river basin using regional bias corrected GCM data

Abstract

Climate change impacts on precipitation pattern have been assessed over upper Bagmati river basin, Nepal. General circulation model (GCM) projections, which are widely used to assess climate change impacts, consist of significant biases due to oversimplification of the global climate system. Bias in daily GCM precipitation was corrected at grid cell scale using regional quantile-based bias correction technique. In this technique, bias correction pattern is established by comparing GCM grid data with nearby observation station data. Concepts of homogeneous precipitation regions were used to transfer statistical characteristics of nearby observation stations to ungauged cells. Calibration and validation of the regional bias correction technique was performed over 1979-2003. Comparative precipitation change assessments were carried out at annual, monthly and daily time scales considering bias corrected precipitation data of 1979-2003 and 2075-2099 periods respectively.