基于SWAT模型的祁连山区最佳水源涵养植被模式研究——以石羊河上游杂木河流域为例

Optimization of vegetation covers in Qilian Mountains Based on hydrological responses by SWAT model:a case study of Zamu River Basin in Upper Shiyang River Basin

以西北干旱区祁连山系杂木河流域为研究区,应用分布式水文模型(SWAT)对该流域的径流进行模拟研究,探讨了流域尺度和微地形尺度7种不同植被组合模式下水文响应特征。结果表明:流域尺度上,单一植被模式在水分收支各分支中能够明显加大流域总蒸散发量,减少流域出山径流量,增加流域的水分蓄变量,为水资源的可持续供给带来时间变异;组合模式明显改善流域水分收支比例,适度减弱流域蒸散发量,增加流域出山径流,为水资源可持续供给提供恒量保证,减弱局地的水资源时间变异程度;微地形尺度上,各种景观类型的水文效应随着海拔高度变化基本一致,径流深随着海拔高度的增加而减小,蒸散发随着海拔高度的增加而增加。不同高度分级中,植被组合模式的不同导致在不同坡度条件下水文效应差异显著,40°坡度是水文效应变化规律发生变化的一个拐点。基于上述分析,提出祁连山区最佳水源涵养效应的生态模式。

The research studied the Zamu River basin in Qilian Mountains in the arid region in NW China with the use of the distributed hydrological model SWAT（ the Soil and Water Assessment Tool that can simulate soil water sediment and nutrient）. This paper discussed hydrological response for different vegetation covers at basin and sub-basin scales. The model was able to represent the hydrological cycle even though some discrepancies were observed,probably due to a lack of sufficient rainfall data. This research investigated seven combined cases：forest-deciduous（ FRSD） ,grassland（ SPAS） ,rang-brush（ RNGB） ,FRSD ＋ SPAS,FRSD ＋ RNGB,SPAS ＋ RNGB,and SPAS ＋ URLD（ in short for Residential-Low Density）. The hydrological responses vary at various spatial scale as well as at various vegetation combinations. At the basin scales,a single vegetation cover would substantially increase the total evapotranspiration amount and basin storage,decrease the runoff,and cause the temporal variations of sustainable water supply. A combination of various vegetation covers would improve the water budget,moderately decrease the total evapotranspiration,increase runoff,ensure the sustainable water supply and decrease the temporal variation of water in the local region. FRSD would increase the soil water capacity and decrease the change of soil water capacity. SPAS would decrease the soil water capacity due to high density roots. Human activity play a negative role in hydrological response in Qilian Mountain and they can reduce the total evapstranspiration and soil water capacity. At the sub-basin scale,the changes of hydrological responses of different vegetation covers showed the same trend as the altitude changes. With the altitude increasing,the depth of runoff decreased and evapotranspiration increased. At one altitude,a change in vegetation would result in different hydrological responses on different slopes,and a slope of 40 degrees is the inflection point where the hydrological responses would change diversely. Based on these analyses,optimized vegetation covers with the best hydrological responses were obtained. FRSD and FRSD ＋ RNGB have very good hydrological response in different terrain in Qilian Mountains. RNGB and RNGB ＋ SPAS also have good hydrological response between 2601 and 3000 m above sea level. FRSD ＋ SPAS performs the good hydrological response between 3000 and 3800 m above sea level. The cold region is above 3800 m above sea level and it＇ s best to keep the current vegetation in the region. According to similar studies that compared the hydrological response for different plants and for different land use,we would suggest that Picea crassifolia and Sabina przewlskii are dominant plants for FRSD,Cupular willow,Potentilla fruticosa and Spiraea salicifolia L. are dominant plants for RNGB,and that Kobresia pygmaea is dominant plant for SPAS.