| Rapid identification of areas suffering serious Eco-environmental Water Deficit (EWD) and dynamic assessment of Eco-environmental Water Use (EWU) are of significance to ecological construction and sustainable utilization of water resources in a catchment. With the similar spirit as the prevailing rapid biological assessment methods for water body, a rapid assessment method in terms of Eco-environmental Water Requirement (EWR) was developed to address this point for different scales of catchments, and a case study was carried out on the Yanhe Basin and Zhifanggou Watershed located on the Loess Plateau.The method proposed herein contains 8 main steps, specifically, (1) partition of the study area into proper units; (2) construction of indicator of EWR (EWRI) for a basin; (3) selection of environmental variables; (4) integration of the data about EWRI and the environmental variables into the units obtained in step (1); (5) pick of typical units as the reference units and construction of reference groups, and the other units as test ones; (6) calculation of memberships of each test unit to all reference groups; (7) calculation of the expected EWRI of each test unit based on its degree of membership to and the average EWRI of each reference group; (8) with the observed and expected EWRIs of each test unit, an indicator of EWD (EWDI) could be calculated to show its severity of EWD.The method was applied to the Yanhe Basin with land use data of 1990 and 2000, and the result showed that the south of Ansai County, the Yan'an build-up surrounding areas and Baota District were suffering serious EWD. A further study was carried out on Zhifanggou Watershed located in south Aansai, a secondary tributary of Yanhe River, with land use data of 15 periods among 1938～1999. The result showed that the variation of its EWU experienced a process of"natural balance - severe EWD - gradual improvement - tending to balance". This was highly consistent with the developed process in the watershed. These applications proved the proposed method of practicability and rapidness. The dominant objective of ecological construction in the study area is to prevent soil erosion. Therefore, this dissertation calculated the EWR of Zhifanggou according to certain objectives of soil conservation. The result showed that given a soil loss tolerance of 1000 t/km~2·a, the EWR of Zhifanggou was about 1.77×10~6m~3, 39.0% of the total annual precipitation, similar to the situation in 1998. Moderately reducing the objective of soil conservation can save a little EWR to some extent.In order to reveal the relationship between"water conservation"and"soil conservation", analytical method of water resource structure was applied to discover the connotation of"water loss". Furthermore, with Zhifanggou watershed as the study area, indicators for soil erosion and water loss were used to address the relationship between them, and the water use for soil conservation under deferent objectives was discussed. The result showed that as the concomitant of soil erosion, water loss reflected the transforming trends of water for entironment to that of latent resource and calamity. From 1938 to 1999, the degree of water loss and soil erosion in Zhifanggou had significant correlativity. The objective of soil conservation could be set to a soil loss tolerance of 1000 t/km~2·a, with a corresponding runoff of 6.77×10~4m~3 which could approximately meet the EWR of the river ecosystem and human water requirement.
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