SWAT model-based quantification of the impact of land-use change on forest-regulated water flow

For most watersheds, land-use change leads to changes in forest-regulated water flow, not only in relation to changes in forest area, but also in relation to conversion of forest and other land-use types. To reveal the impacts of land-use change on forest-regulated water flow, this study proposes computational formulas for multi-time scale analysis of the regulated water flow in a watershed with various land-use types, whose spatial distribution is discontinuous in the hydrological response unit (HRU) scale using the Soil and Water Assessment Tool (SWAT). The impacts of land-use change on forest-regulated water flow were then computed with the formulas and a transfer matrix between the forest and other land-use types. The Jinjiang River Watershed which covers an area of approximately 5042 km(2)& nbsp;in the southeast coast of China, was selected as the study area and the results showed that (1) The annual forest-regulated water flow in the Jinjiang River Basin was 271.41-565.25 mm. The monthly flow ranged from-29.15 mm to 154.59 mm, which was positive for most months of the year. The forest-regulated water flow was positive in extreme precipitation period, and negative in extremely dry period. Forest-regulated water flow significantly varied with various time scales. (2) During 1985-2006, The forest area in the Jinjiang River basin decreased from 3094.84 km(2)& nbsp;to 2805.81 km(2), which led to a reduction of 44.99-83.51 mm in annual, 0.54-6.36 mm in monthly, and 0.73-5.30 mm in daily forest-regulated water flow, respectively and (3) the proposed method is suitable for multi-time scale analysis of regulated water flow of various land-use types whose spatial distribution is discontinuous in a watershed. It provides a newer approach for evaluating the impacts of land-use changes on water flow regulation function in watersheds with respect to separate land-use types and their spatial conversions.