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

Abstract

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 km2 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 km2 to 2805.81 km2, 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.