Assessing future rainfall projections using multiple GCMs and a multi-site stochastic downscaling model

Impact of global warming on daily rainfall is examined using atmospheric variables from five General Circulation Models (GCMs) and a stochastic downscaling model. Daily rainfall at eleven raingauges over Malaprabha catchment of India and National Center for Environmental Prediction (NCEP) reanalysis data at grid points over the catchment for a continuous time period 1971-2000 (current climate) are used to calibrate the downscaling model. The downscaled rainfall simulations obtained using GCM atmospheric variables corresponding to the IPCC-SRES (Intergovernmental Panel for Climate Change - Special Report on Emission Scenarios) A2 emission scenario for the same period are used to validate the results. Following this, future downscaled rainfall projections are constructed and examined for two twenty year time slices viz. 2055 (i.e. 2046–2065) and 2090 (i.e. 2081–2100). The model results show reasonable skill in simulating the rainfall over the study region for the current climate. The downscaled rainfall projections indicate no significant changes in the rainfall regime in this catchment in the future. More specifically, 2% decrease by 2055 and 5% decrease by 2090 in monsoon (JJAS) rainfall compared to the current climate (1971–2000) under global warming conditions are noticed. Also, pre-monsoon (JFMAM) and post-monsoon (OND) rainfall is projected to increase respectively, by 2% in 2055 and 6% in 2090 and, 2% in 2055 and 12% in 2090, over the region. On annual basis slight decreases of 1% and 2% are noted for 2055 and 2090, respectively. ⺠We model daily rainfall over an Indian catchment using a statistical downscaling model and atmospheric data of five GCMs. ⺠The model is calibrated using rainfall and reanalysis data for the years 1971-2002. ⺠GCMs data for the periods 2046-65 and 2081-2100 is used to obtain rainfall projections. ⺠We find reasonable skill in simulating daily rainfall over the study region for the current climate. ⺠We find no significant changes in the temporal and spatial structure of annual rainfall in the future by all the models.