Evaluating climate extremes and their association with floods in the Baro Akobo River basin using CMIP6 and hydrological modelling

Recent studies indicate climate change-driven extreme weather events have led to frequent flooding in many East African countries, including Ethiopia. This study evaluates climate extremes and their association with floods in the Baro Akobo River Basin, Ethiopia, using CMIP6 climate models and HEC-HMS hydrological modeling. We use daily precipitation and temperature from 30 meteorological stations, and 12 CMIP6 global climate models (GCMs) under two shared socioeconomic pathways (SSPs), SSP2-4.5 and SSP5-8.5 scenarios. The GCMs are evaluated at the daily time scale with observed data over the period from 1985 to 2014, resulting in MPI-ESM1-2-HR, INM-CM4-8, FGOALS-g3, and GFDL-ESM4 the top four best-performing models in the basin. We utilize the expert team climate change detection Indices to assess climate extremes in the basin, focusing on five precipitation-based and four temperature-based indices due to their anticipated correlation with flood events. We then simulate peak discharge at the basin’s outlet using the HEC-HMS hydrological model to correlate annual maximum peak flow (Qmax) with climate extreme indices. The results show that during the mid-century (2041–2070), all precipitation extremes, except for consecutive wet days (CWD), demonstrate a strong correlation with Qmax, characterized by correlation coefficients ranging from 0.54 to 0.87 under both scenarios. In contrast, by the end of the century (2071–2100), CWD and the Maximum 1-day precipitation (Rx1day) exhibit a weak correlation; however, Total Precipitation (PRCPTOT), Maximum 5-day precipitation (Rx5day), and Numbers of Heavy Precipitation Days (R10mm) display strong correlations, ranging from 0.55 to 0.85 for both scenarios. All temperature extremes have a relatively strong positive correlation with Qmax except for the coldest night temperature (TNn) during the mid-century in both scenarios. During the end-century, except for the Warmest Night Temperature (TNx), all temperature extremes negatively correlate with Qmax. The results further reveal an increasing trend in PRCPTOT, Rx5day, and R10mm during the mid and end of the century, suggesting a greater likelihood of heavy precipitation events that may elevate the flooding risk in the basin.,. Therefore, further research is recommended to evaluate the extent and impact of the anticipated flooding in the basin, which will help devise appropriate mitigation strategies.