Rapid Assessment Method for Eco-Water Deficit in Catchments

Eco-water deficit (EWD) is the difference between the eco-water required (EWR) for maintaining health of a given ecosystem and the actual eco-water used (EWU) by the same ecosystem. EWD is of significance for assessing the effectiveness of eco-water allocation and for sustainable water resources management. This paper proposes a rapid assessment method for catchment EWD. A framework is established to describe the concepts, characteristics and impact factors related to EWR for catchments containing various types of sub-ecosystems. The indicator of EWR (EWRI) of a catchment is defined as the sum of products between the weight representing the level of importance of each sub-ecosystem (sub-catchment) to EWR and its area percentage over the total area. By means of a series of processes of partition of spatial units, selection of reference units, classification of reference groups, determination of environmental variables, and identification of matching groups for the test units, EWDI, an indicator related to the relative degree of EWD severity of each test unit is calculated by subtracting the ratio of its observed and expected EWRI from one and then used to identify areas with most serious eco-water deficit. A case study is conducted in the Yanhe River catchment in north China based on land use data surveyed in 1990 and 2000. The results revealed that the south part of Ansai County, most of Baota District and the areas around Yan'an City experienced severe shortage of eco-water. The case study demonstrated the applicability of the rapid assessment method for EWD in practice.