Advances in clarification of the driving forces of water shortage in Haihe River Catchment

Including Beijing, Tianjin, Hebei and three surrounding provinces, Haihe River Catchment is facing an increasing shortage of water resources. This paper summarized our research progress on the driving mechanisms of water resources change including reasons for runoff changes, spatial variations and temporal changes of agricultural water use, and outflow of virtual water through external food supply. Firstly, by using the sequential Mann-Kendall to determine the abrupt changes in eight sub-catchments of Haihe River Catchment and traditional Mann-Kendall test for the period 1960-1999 to identify the basic trend of precipitation and runoff, it was confirmed that runoff reduction started since 1970s, and generally became statistically significant from 1978 to 1985. Through correlation comparisons for precipitation and runoff for the periods prior to and after abrupt runoff changes, human activity, rather than climatic change, was identified as the main driving factor of runoff changes. By using SWAT model, it was concluded that human influence on agricultural water demand contributed to 76% of runoff decline at the beginning of the China's rural reform. Secondly, through crop modeling, crop water demand calculation by crop coefficient and ET, and remote sensing methods, spatial and temporal distribution of agricultural water demand in the Haihe Plain were quantified. Changes of agricultural water demand were evaluated. This in turn laid the basis for surface water reallocation following the completion of the South-to-North Water Transfer (SNWT) project. By comparing agricultural water consumption, groundwater level change, and water supply from the SNWT canal, it was estimated that there could be a relative balance of water demand and supply in the piedmont plain with the designed water supply from SNWT upon strong limitation on further water-consumption increase especially for newly developed landscapes such as lakes, rivers, wetland, water consuming woodland, and etc. In the coast plain, water shortage would remain for the long-term, meanwhile more water supply together with brackish water use was to be developed. While agriculture placed the greatest demand on water resources, reducing the cultivation of water-consuming crops might be the most effective way to reduce agricultural water use. However, taking food demand into consideration, sustaining the balance between regional water and food security was a growing challenge. To solve such problem, we studied NEXUS or interlinkage among land use, water consumption, food production (Land-Water-Food NEXUS) in Beijing-Tianjin-Hebei Region. Virtual water flow embedded in food transfer was evaluated. According to our estimation, nearly 9×10⁹ m³ virtual water and 2×10⁶ hectares cropland were currently used for producing 1.2×10⁷ tons maize for external food supply, which highly resulted in the locally developing water shortage. Controlling food production and virtual water outflow shall be a suitable and very necessary way to alleviate the pressure of water shortage facing the quick developing strategies of Beijing-Tianjin-Hebei Region and the newly lunched Xiong'an New District.