An ensemble-based projection of future hydro-climatic extremes in Iran

Climate change poses a significant global challenge, impacting both the natural and socio-economic functioning of the world. Iran, is already experiencing significant changes in hydro-climatic patterns. Here, we introduce and employ an assessment framework to evaluate the impacts of climate change on hydro-climatic extremes for 576 catchments across Iran. We used future projections of five Regional Climate Models (RCMs) from the Coordinated Regional Climate Downscaling Experiment (CORDEX) for two time periods, the near future (2024-2050) and far future (2051-2080) and two Representative Concentration Pathway (RCP) scenarios, RCP 2.6 and RCP 8.5. These projections were bias-corrected and used to drive the HBV hydrological model for estimating changes in extreme streamflow, characterized via 19 hydro-climatic indices. Results show that, based on the median values of the RCM ensemble, most study catchments will experience modest precipitation reductions but with amplified intensity and frequency of precipitation events and substantial rises in air temperature. Most extreme precipitation indices show noticeable upward trends under both RCP scenarios, with significant increases in extreme temperatures, especially under RCP 8.5. An increase in the annual maximum 1-day streamflow index is projected across approximately half of the catchments, with the most notable rise in the northeastern and southeastern regions of Iran. Moreover, northeastern Iran can expect significant increases in the annual minimum 7-day streamflow index, in both the near and far future, and under both RCP scenarios. Our findings offer valuable insights into the patterns of hydro-climatic extremes within Iran in response to climate change and have the capacity to inform decision-makers to develop effective adaptation and mitigation strategies.