Application of Climate Projections and Monte Carlo Approach for Assessment of Future River Flow: Khorramabad River Basin, Iran

This paper assesses the impact of climate change uncertainties on the Khorramabad River basin’s runoff in Lorestan Province, Iran. Five atmosphere-ocean general circulation models’ (AOGCMs) [Hadley Centre Coupled Model, version 3 (HadCM3), Center for Climate System Research-National Institute for Environmental Studies (CCSR-NIES), Commonwealth Scientific and Industrial Research Organization Mark 2 (CSIRO-MK2), Coupled Global Climate Model (CGCM2), and Geophysical Fluid Dynamics Laboratory (GFDL-R30)] projections of rainfall and surface temperature were applied to simulate climate in the periods 2040–2069 and 2070–2099 under the A2 and B2 greenhouse gases (GHGs) emissions scenarios. The AOGCM projections showed an increase in temperature and a decrease in rainfall over the future periods. The ranges of climate change scenarios were determined, and the models’ results were weighted for each month based on the $k$-nearest neighbors (KNN) method. Multiple time series of temperature and rainfall were generated with the Monte Carlo method based on their monthly probability distributions. The identification of unit hydrographs and component flows from the rainfall, evapotranspiration, and streamflow (IHACRES) hydrological model was calibrated and validated, and subsequently applied to simulate future river flow with downscaled climatic data from (1) five AOGCMs, and (2) a developed Monte Carlo model. The results showed that the average annual long-term runoff calculated with the developed Monte Carlo approach in the period 2040–2069 under the A2 and B2 scenarios decreased by 7.76% and 10.63%, respectively. The average annual runoff decreased by 13.06% and 29.49%, respectively, relative to the baseline period in the period 2070–2099 under the A2 and B2 scenarios. These results indicate a worsening availability of runoff through the remainder of the 21st century in the study region.