Combined impacts of climate change and human activities on blue and green water resources in the high-intensity development watershed

Abstract. Sustainable management of blue and green water resources is vital for the stability and sustainability of watershed ecosystems. Although there has been extensive attention to blue water (BW) which is closely related to human beings, the relevance of green water (GW) for ecosystem security is typically disregarded in water resource evaluations. Specifically, there is a scarcity of comprehensive study on the detection and attribution of variation of blue and green water in the Dongjiang River Basin (DRB), an important source for regional water supply in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) of China. Here we assess the variations of BW and GW scarcity, quantify the impacts of climate change and land use change on BW and GW in DRB using a multi-water-flux calibrated Soil and Water Assessment Tool (SWAT). Results show that BW and green water storage (GWS) in DRB increased slowly with a rate of 0.14 and 0.015 mm a^-1, respectively, while green water flow (GWF) decreased significantly at a rate of -0.21 mm a^-1. The degree of BW and GW scarcity in DRB is low, and the per capita water resources in more than 80 % of DRB exceed 1700 m³ capita^-1 a^-1. Attribution results show that 88.0 %, 88.5 %, and 39.4 % of changes in BW, GWF, and GWS results from climate change, respectively. Both climate change and land use change have decrease BW, while climate change (land use change) decrease (increase) GWF in DRB. These findings can guide to optimize the allocation of blue and green water resources between upper reach and lower reach areas in DRB and further improve the understanding of blue and green water evolution patterns in humid regions.