Impact analysis of climate change on near future streamflow using CORDEX-SA datasets in a hilly watershed

Abstract

The study analyses the impact of projected increase in temperature and rainfall on streamflow in the Barak Basin, Northeast India. The forest dominated rain-fed river basin up to Annapurna Ghat (Silchar) near the border of Bangladesh covers an area of 19004 Sq. Km. There has been an increasing occurrence of flood events in the basin due to decreasing forest cover. The study attempts to analyze the impact of climate change on river streamflow for the near-future (NF) (2021-2050) based on the multi-model ensemble mean (MME) of 6 Regional Climate Models (RCMs) from CORDEX-SA consisting of CNRM-CERFACS-CNRM-CM5, CCCma-CanESM2, IPSL-IPSL-CM5A-MR, MPI-M-MPI-ESM-MR, CSIRO-QCCCE-CSIRO-Mk3-6-0, and NOAA-GFDL-GFDL-ESM2M, using the SWAT hydrological model. These model datasets are bias-corrected using the distribution function.  Projection considered RCP4.5 and RCP8.5 emission scenarios. The study setup the SWAT model based on the LULC of 2011 and observed climate datasets for the period 1990-2020. The base model is calibrated and validated using two observed discharge data for the period (1995-2020).  Projected temperature (Tmax and Tmin) increases in near future while rainfall increases in the first half of monsoon-June and July- and post-monsoon and decreases in the second half of monsoon in both scenarios. In contrast, in the pre monsoon projected rainfall is in excess of observed under RCP8.5. The discharge shows considerable decrease in both the emission scenarios during the dry winter season while there is increase in discharge during the post monsoon. During monsoon, the discharge marginally decreased with respect to the historical observed discharge under RCP 8.5. The monthly mean discharge distribution pattern closely follows the rainfall mainly because the basin is rain-fed.