Projection of the combination of land use and climate change impacts on runoff in the Bojnourd catchment under CMIP6 Scenarios

Abstract

Abstract Climate change and land use changes have a significant impact on the hydrological cycle in river basins and water resources in arid and semi-arid regions of the world. Evaluating these changes is necessary to reduce their effects on the basin and develop a suitable strategy to minimize their impacts. Using the LARS-WG and SWAT combined model, this study evaluated the simultaneous effects of land use changes and climate change on the hydrological response of the catchment in the Bojnourd catchment in North Khorasan province, Iran. First, the changes in climate parameters during the years 2049-2020 in the two synoptic stations of Bojnourd and Asadli were investigated in the conditions of climate change using SSP245 scenarios as the medium scenario and SSP585 (pessimistic scenario) from the sixth IPCC CMIP6 report. SUFI2 algorithm is used in SWAT-CUP software to validate and confirm the SWAT model. In the calibration stage, the Nash-Sutcliffe index (NS) coefficient for the basin was 0.59 and in the confirmation stage, this index was 0.50 percent. In this research, land use changes were analyzed and predicted using ENVI software and the CA-Markov model for the years 2001, 2019, and 2040. The Kappa coefficient has been used to determine the accuracy of the land use map and its value for 2001 and 2001. 2019 are 0.91 and 0.95 percent respectively. Human-made land use changes accounted for the most land use changes between 2001 and 2040, which almost tripled in about 40 years. Also, the ratio of pasture has decreased from 61% to about 50%. On the other hand, the share of barren land will increase from 22% to about 27% by 2040. However, the precipitation will be different in Asadli and Bojnourd stations because the first shows a decrease and the second shows a very small amount of increase. The results of the SWAT model showed that the combined effect of both climate change factors and land use changes will reduce the runoff of the basin during the coming period so that the average monthly discharge at the outlet of the basin from 1.26 cubic meters per second in the base period to about 1.04 cubic meters per second (17.5 percent) will decrease in the coming period. The biggest decrease in the ssp585 scenario, as a pessimistic scenario without calculating the effect of land use changes in 2040 and only examining the effect of climate changes in the future period, the basin runoff will decrease by 0.9 cubic meters per second (28.5%). In fact, in both scenarios, the watershed runoff decreases, while the effect of land use change increases the watershed runoff, and this increase is less than the effect of climate change in the watershed.