Investigation of the effects of climate change on hydrological drought and pattern detection for severe climatic conditions using CCT and SWAT models in the semi-arid region—Case study: Karkheh river basin

Drought causes an imbalance in the hydrological condition of the area. Climate change is exacerbating this situation. In this study, the hydrological drought under the influence of climate change in Karkheh river basin was investigated using the SRI index. For this purpose, the Soil and Water Assessment Tool model was calibrated (1990 to 2009) and validated (2010 to 2018) using data from 17 meteorological stations and 11 hydrometric stations. Then, based on the runoff simulated by the model, the index in all sub-basins for the base period (1990 to 2018) is calculated. By introducing the microscale results of 5 climate models in the Climate Change Toolkit program under RCP 2.6 and RCP8.5 scenarios to the SWAT model, the SRI index was simulated for the near future (2043 to 2071) and the distant future (2072 to 2100); and its intensity, duration and frequency were compared with the baseline period. The results show that hydrological drought will decrease in the near future for both scenarios; while in the distant future this result will be reversed. The CCT model includes the Critical Consecutive Day Analyzer (CCDA), whose application in the region showed that at least once a wet period similar to the 2018 flood conditions will be observed for the near future.There will also be at least one similar drought in 2014 for the distant future in the region. However, in previous climate studies, future events have not been calculated based on identifying the pattern of those events in the past.