Climate change effects on reliability of water delivery in downstream of Karkheh river basin and its adaptation strategies

Increasing population and water demands caused a considrable challenge for decision makers in water sector. Also climate change in near future will exacerbate the situation. This study evaluated the impacts of climate change on water supply reliability and allocation in Karkheh river basin. In this study for assessing the effects of climate change on Karkheh river basin water supply، 15 GCMs and several greenhouse gas emission scenarios were applied to evaluate the changes of precipitation and temperature for time horizon 2050s. Then multiple river flow time series (RFTS) were generated by feeding future temperature and precipitation into a calibrated rainfall-runoff model. Due to the uncertainty of GCMs for generating future temperature and precipitation، the forecasted river flow for mid-century had a wide range of changes between -50% to +36%. Therefore for dealing with uncertainty of GCMs، the hierarchical clustering method was used to identity 5 clusters from 35 RFTS and subsequently 1 representative member from each clusters. Also three management strategies of crop pattern change، increasing irrigation efficiency and water reuse for adaptation of climate change was evaluated. Results showed that building new dams in upstream will decrease the reliability of agriculture water supply to less than 70%. Also، the water reuse with more than 90% reliability، is the most effective strategy for dealing with climate change. The crop pattern change includes comparable water demand reliability، but less costs. However، execution of crop pattern change is a low-cost strategy، depending on farmers cooperation.