基于SWAT模型的湘江流域土地利用变化情景的径流模拟研究

土地利用变化对径流产生重要影响, 显著影响到流域生态的可持续发展。本文应用流域分布式水文模型SWAT, 对湘江流域内5个水文站点(湘潭、株洲、衡山、衡阳、归阳)的月径流进行了模拟。选取1998~2002年作为模型校准期, 以Nash-Sutcliffe效率系数(NSI)和决定系数(R²)为评价指标, 率定出7个模型敏感参数, 并用2003~2007年的月径流进行模型验证。研究表明, 除归阳站点外, 其余4个站点月径流模拟的R²和NSI都高于0.82, 有的甚至达到0.92, 说明模拟效果较好。在此基础上, 以《湖南省土地利用总体规划(2006-2020)》为依据, 设置了3种土地利用情景模式, 以研究不同土地利用方式对径流的影响程度。结果显示, 土地利用变化对水文过程影响比较显著, 情景1中, 随着165.40 km²的耕地转为林地以及793.91 km²的耕地转为草地, 径流深模拟输出减小1.28 mm; 情景2中, 随着8 173.96 km²的林地转为耕地以及337.56 km²的耕地转为建设用地, 径流深模拟输出增加15.61 mm; 情景3中, 随着500.02 km²的未利用地转为耕地, 径流深模拟输出增加1.16 mm。因此, 增加林地和草地面积将减少径流, 而耕地和建设用地的增加导致径流的增加。在对湘江流域进行土地利用规划时需要综合考虑水文效应和经济效益, 充分认识人类活动对水资源的影响。

Using SWAT to simulate runoff under different land use scenarios in Xiangjiang River Basin

Runoff varies with land use types, which in turn affects eco-sustainable development of river basins. In this study, SWAT (Soil and Water Assessment Tool) was used to simulate monthly runoff in relation to land use in Xiangjiang River Basin (XRB). Observed runoff data were collected from the Xiangtan, Zhuzhou, Hengshan, Hengyang and Guiyang monitoring stations. A total of seven model parameters were calibrated with data for 1998~2002 and validated for 2003~2007. The coefficient of determination of linear regression (R²) of the observed and simulated monthly runoff and the corresponding Nash-Sutcliffe Index (NSI) were used to evaluate the model performance. With the exception of Guiyang station, all R² and NSI values were higher than 0.82, with some as high as 0.92. The results showed that SWAT reliably simulated runoff in XRB. Given the high model performance, three scenarios (based on the 2006~2020 comprehensive land use planning in Hunan Province) were used to study the impact of land use type on runoff in XRB. Compared with the existing land use conditions, predicted runoff dropped by 1.28 mm under scenario 1 (where 165.40 km² of agricultural land was changed into forest land and 793.91 km² of agricultural land changed to grassland). Under scenario 2 (where 8 173.96 km² of forest land was reclaimed for agriculture in the upstream basin and 337.56 km² of agricultural land in downstream basin put under urban developed), predicted runoff rose by 15.61 mm. In scenario 3 (where 500.02 km² of unused arable land was reclaimed for agriculture), predicted runoff increased by 1.16 mm. The scenario simulation suggested that runoff dropped under increasing forest land and grassland areas and decreasing paddy field and urban areas. Hydrological effects, economic benefits and human activities were identified as critical factors of runoff and water resources availability in the basin. It was concluded that these factors should be fully taken into account in land use planning and development in XRB.