Ecological conservation and high-quality development of the YRB (Yellow River Basin) has been adopted as a national strategy. However, the ecological environment of the YRB is fragile and it has degraded in recent years. Here we proposed an ecological degradation index system based on the Pressure-State-Response (PSR) model and evaluated trends in ecological degradation of the YRB using the Mann-Kendall trend test. We found an upward-downward-upward trend in the ecological degradation index (EDI) during the period of 2000–2019. We also observed an intensifying degradation of eco-environment from the upper to the lower YRB. Meanwhile, 69.9% of the YRB is under degraded eco-environment, while 29.5% of the YRB is dominated by improved eco-environment. Specifically, the ecological degradation intensity of Henan and Shandong Province with dense population and rapid economic development is the highest. Due to active and effective improvement measures taken by the government, the degradation intensity has been having a decreasing tendency. However, higher degradation intensity of eco-environment of the YRB should arouse human concerns. As to the driving factors, human activities can be regarded as the major driving factors for degraded eco-environment, and water stress and economic development exert increasing impacts on the eco-environment of the YRB. Our finding can provide a decision-making basis for the ecological management and high-quality development of the YRB.

The ecological conservation and high-quality development of the Yellow River basin (YRB) has been adopted as a major national strategy of China. However, the YRB is still afflicted by floods. Here, we proposed a flood risk indicator using direct economic loss degree and improved the SNRD (station-based nonlinear regression downscaling model) and simulated extreme precipitation processes. The correlation coefficient of downscaled average extreme precipitation of CMORPH and CMIP6 data reached 0.817. Moreover, we evaluated flood risk and flood hazard across the YRB based on the sixth phase Coupled Model Intercomparison Project (CMIP6) data under different SSPs. Under SSP126, SSP245, and SSP585 scenarios, the areas with increasing flood hazards during 2015–2045 accounted for 65.2, 69.0, and 64.5% of the entire YRB. In the spatial pattern, flood hazards decreased from southeastern to northwestern parts of the YRB. When compared with the spatial pattern of flood risks in 2015, regions with high flood risks expanded slightly and regions with low flood risks shrunk slightly. Higher flood risks can be observed in the middle and lower YRB and particularly in the lower YRB. These findings are critical for the mitigation of flood risk across the YRB under warming climate.

The ecological conservation and high-quality development of the Yellow River Basin (YRB) has been declared as a major national strategy of China. Surface water availability (precipitation minus evapotranspiration, PME) poses challenges to the sustainability of ecosystems of the YRB. Noteworthy is that the Mongolian section of the YRB (IMYRB) is a critical ecological barrier in Northern China. Soil moisture (SM) changes are highly sensitive to PME and important for regional ecological security. However, SM vs. PME interactions and relevant mechanisms within the IMYRB are poorly understood. We found significant decreases in SM and PME over the east IMYRB (r = 0.7, p < 0.05). During the wet (July, August, and September) and dry (April, May, and June) seasons, as well as the whole year, decreased SM drives increased PME through land-atmosphere interactions over more than 90% of the IMYRB. Reduction in SM decreased evapotranspiration over more than 80% of the IMYRB, increased surface temperature across more than 79% of the IMYRB, boosted atmospheric vertical ascent over more than 75% of the IMYRB, and enhanced moisture convergence and PME. This study highlights the land-atmosphere interactions over the IMYRB, implicating basin-scale impacts of climatic changes on water resources.