Drought impacts on blue and green water: A spatial and temporal analysis

Abstract

Global warming is exacerbating water security risks in watershed ecosystems. Hence, it is especially crucial to examine how blue and green water respond to drought in watershed ecosystems. This study utilized the Soil and Water Assessment Tool (SWAT) to investigate temporal and spatial variations in blue and green water resources within the Wujiang River Basin (WRB) across three distinct ecosystems: agriculture, forest, and grassland. Concurrently, the Standardized Precipitation Evapotranspiration Index (SPEI) was employed to assess drought risk in the basin, and the relationship between typical ecosystem blue and green water resources and drought response was further explored. The study's results revealed the following key findings: (1) From 1985 to 2014, the basin recorded an average total of 54129.8 × 106 m3 and 46227.7 × 106 m3 of blue and green water, respectively. Notably, forest ecosystems contributed 50 % and 62 % to the blue and green water resources, respectively. (2) In typical ecosystems, temporal changes in both blue and green water exhibited a pattern of initial increase followed by a decrease. Furthermore, spatial changes along the upstream-to-downstream gradient showed an initial decrease, followed by an increase, and ultimately another decrease. (3) In typical ecosystems, blue water is more affected by dry and wet conditions, while green water is influenced by a combination of dry and wet conditions and land use changes. (4) As drought intensity rises, both blue and green water resources in typical ecosystems decrease. Notably, green water in forest ecosystems is less affected by drought intensity, which contributes to maintaining water resource security in watershed ecosystems. These study findings provide a robust scientific foundation for water resource management and drought mitigation strategies in the basin.