Streamflow decline threatens water security in the upper Yangtze river

Abstract

The annual streamflow in the upper Yangtze River (UYR) declined by 36.6 billion m3 from 1961 to 2015. However, the contributions to this streamflow decline from different tributaries and the underlying causes remain unclear. Here we quantify the streamflow decline in the UYR and the impacts of climate change and human activities using a distributed hydrological model and statistical methods. Results show that the streamflow decline increased from the upstream to downstream regions. Combining hydrological simulation and statistical analysis, the contributions of climate change, human water consumption, reservoir impoundment and human-induced vegetation change on streamflow decline are estimated to be 62.5%, 19.7%, 18.4% and 1.8%, respectively. Specifically, human water consumption growth is consistent with the spatial pattern of population growth and industrial development, and the reservoir impoundments are mainly located in the middle and lower parts of the mainstream. In the Jialingjiang, the tributary with the largest drainage area in the UYR, human activities account for 63.6% of the streamflow decline, with the largest decline induced by human water consumption growth. Under climate change and population growth, the population under water stress (water resources available less than 1000 m3/capita/yr) increases in the Mintuojiang and Jialingjiang, where the major cities are centralized and the population density is high. This study provides a new perspective for understanding the status of water resources in the UYR and offers insights into the sustainable utilization of water resources in the future.