Frequent drought and flood events in the Yellow River Basin, increasing future drought trends in the middle and upper reaches

Under global warming, the Yellow River Basin (YRB), serving as an ecological barrier and climate-sensitive region in northern China, faces severe challenges such as frequent extreme droughts and floods, as well as intensifying water resource supply–demand conflicts. To systematically assess the evolution of droughts and floods in the YRB, this study utilizes observational data from 137 meteorological stations and CMIP6 scenario models, employing the dual-index system of the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) to quantitatively analyze historical drought and flood characteristics, and project future trends under different scenarios. The results indicate that both SPI and SPEI effectively identify drought and flood events, with SPEI demonstrating superior sensitivity to extreme droughts and floods due to its integration of evapotranspiration effects. From 1956 to 2020, the basin’s drought index increased at a rate of 0.003–0.025 per decade, while the flood index changed at a rate of −0.006–0.039 per decade. Droughts were frequent in the middle and upper reaches (30.61 % severe droughts), while flood risks were prominent in the lower reaches (6.25 % extreme floods). Under SSP3-7.0 and SSP5-8.5 scenarios, drought-dominated patterns intensified (severe droughts reaching 62.92 %), and extreme floods showed an increasing trend in the middle and lower reaches. Therefore, the middle and upper reaches should prioritize building drought-resilience systems; the southern and lower reaches should enhance flood-defense infrastructure. Reservoir operations should be optimized using 1–6 months of drought and flood warnings and coupled with groundwater replenishment strategies for 12–24 months of drought cycles.