Attribution of water resources evolution in the highly water-stressed Hai River Basin of China

Many observations and studies have shown that water resources amount in the Hai River Basin decreased significantly over the last half of the twentieth century. This study attempts to attribute the observed changes in the water resources amount in the basin over a 40 year period (1961-2000) to different factors, including natural climate variability, climate change induced by anthropogenic forcing of greenhouse gas emissions (referred to as anthropogenic forcing hereafter), and local human activity. First, the temporal variation of the annual water resources amount in the basin during the past 40 years is analyzed by employing the moving-average method, the linear regression method, and the Mann-Kendall method. Second, through setting different scenarios, the effects on the water resources amount due to different factors, including natural climate variability, anthropogenic forcing, and local human activity, are obtained using the parallel climate model, the distributed hydrological model water and energy transfer processes in large river basins, and the statistical downscaling model. Third, the fingerprint-based attribution method is used to obtain the signal strengths of observed changes in water resources amount during 1961-2000 and changes in the water resources amount under different scenarios. Finally, by comparing the signal strengths, the observed changes in water resources amount in the basin can be attributed to different factors. The results indicate that natural climate variability and local human activity may be two factors responsible for the observed changes in the water resources amount during the past 40 years in the basin, with local human activity being the main factor and accounting for about 60% of the changes.