Water scarcity in the Yellow River Basin under future climate change and human activities.

Under global climate change and pressure from human activities, water scarcity is becoming a major concern in the quest for regional sustainable development in the Yellow River Basin (YRB). This study integrates scenarios of climate change and human activities under the Representative Concentration Pathway (RCP4.5 and RCP8.5) with a watershed-scale hydrological model, and uses the Water Use-to-Availability Ratio (WUAR) to study future water scarcity over six sub-catchments in the YRB. It further investigates the relationship between the future water scarcity and hydroclimatic and anthropogenic drivers. The results suggest that the average WUAR under both RCP4.5 and RCP8.5 will likely exceed the water scarcity threshold (WUAR >20%) and will reach up to 39.9 and 44.7%, respectively. The average WUAR for the upstream and downstream sub-catchments will likely range from 23.8 to 51.6% under RCP4.5 and from 25.5% to 73.8% under RCP8.5, indicating moderate to severe and moderate to extreme water scarcity, respectively. Future WUAR correlates negatively (r-value = -0.85) with the streamflow drought index (SDI) in the upstream sub-catchments, i.e., hydrological drought will likely intensify water scarcity. Conversely, WUAR and SDI would be positively correlated (r-value = +0.70) in the downstream sub-catchments, i.e., water scarcity will become severer despite decreasing severity of hydrological drought. Under climate change, water scarcity in these sub-catchments will exhibit high dependency (Kendall τ correlation coefficient = 0.84) on water-use patterns than on water availability. The regression analysis indicates that the WUAR will increase significantly (p < 0.05) with projected woodland, cropland, and buildup areas under RCP4.5. This relationship will become even more significant (p < 0.01) under RCP8.5. This study provides insights into the potential drivers of future water scarcity in the YRB, which is likely to confront water supply crises. The study should help policymaking towards attaining sustainable water management in the basin.