Based on the past 50 a data about runoff volume, sediment discharge as well as sediment accretion from hydrographic stations, and 10 a data about water quality from pollution stations, a method for measuring the instream flow requirement supported by experiential models and GIS spatial analysis was put forward. Additionally, the changes characters of instream flow requirement for ecological environment and economic development have been addressed from spatial-temporal dimensions. The results showed that the ecological water requiement of the main river systems in Yan'an region reached to 1.0619 billion m3, the surface water for economic exploitation was 0.244 5 billion m3; the instream flow requirement for sediment transportation determined the integrated ecological water requirement; the water need for sediment transportation in flood season occupied over 80% of that in all year, which indicated the runoff volume is larger and sediment transport competency is higher in flood season; the instream flow requirement for sediment transportation from 1950s to 1970s was comparatively higher, and the requirement from 1980s to 1990s presented a decreasing tendency, which accounted for environment in study area had been improved gradually and sediment in rivers was reduced obviously.

GIS spatial analysis; river systems; ecological water requirement; spatial-temporal character; Yan′an city