Trend analysis for blue and green water resources in the Weihe River basin of Northwest China during the past thirty years and in the near future

Climate change is an important factor affecting the availability of both blue and green water resources. Analyzing changing trends of green and blue water enhances our understanding of the potential influences climate change may have on different water sources, subsequently informing the development of water resources management. In this study, we simulated blue water flow, green water flow and green water storage by using the Soil and Water Assessment Tool (SWAT) at the Weihe River basin. We then analyzed the changing trends from 1972 to 2012 at different spatial scales by using the Mann-Kendall (M-K) and Theil-Sen Median (TSM) methods. The M-K and TSM analyses showed that the green water flow, blue water flow and the green water storage were decreased from 1972 to 2012 at the whole river basin. At the sub-basin level, the change of blue/green water trends varied among locations within a basin. The Hurst exponent results indicated that the blue and green water resources will be decreased at the whole river basin, but their future change will be different at the level of sub-river basin. For the Beiluohe River basin, the blue water flow will continue to increase, while the green water flow and green water storage will decrease. However, the green water storage will continue to increase in the Jinghe River basin, while the blue water flow and the green water flow will decrease.