The Study Of Responding Relation Between Land Utilization/coverage Changes And The Eco-hydrology In The Typical Basin Of Shiyang River

Hexi region is one of Chinese famous commodity grain bases, and the Shiyang River Basin in Hexi is a region with comparatively developed agricultural economy, as well as a region with extremely fragile ecology in the arid area of Northwest China. There are diverse ecological types within the region, but due to the unique geographical environment, climate and gradual impact of unreasonable exploitation in the process of human development, the ecological environment becomes very fragile. Worse still, a series of ecological environment problems such as groundwater recession, land sandification, aggravating salinization and vegetation degradation appear, and a change of land utilization is obvious. As the main source of water recharging in the Shiyang River Basin, forests in the upstream are key to the security of ecological and economic development in this basin and play an important role in water and soil conservation and prevention and control of desertification in the midstream and downstream basin. Therefore, in order to reveal the relations between forest coverage changes and runoff in the Basin and improve the ecological environment in the area, it has important value to do an in-depth study about the influence of land exploitation and forest coverage changes in the upper reaches of the Shiyang River on the hydrology and ecology in this area.To further study the correlation between the variation of the forest landscape pattern and the runoff in Northwest and their regulating effect, this paper selects4rivers in the central of the upstream of Shiyang River—Huangyang River, Zamu river, Jinta River, Xiying River as objects of study. The four rivers run together into Shiyang River’s main stream. After flowing into Hongya Mountain Reservoir, the stream runs into Minqin Basin, forming the hydrographic system of six rivers. The application takes Landsat/TM in1999to2009as a data source. With the support of desktop GIS, it takes advantage of the software of Fragstats to interpret every landscape types. Through analyzing the variation trend of land utilization and the runoff of rain water in the six drainage basins, it elaborates the influence of the variation of land utilization, forest coverage and precipitation to the runoff formation process. Moreover, it takes advantage of the distributed hydrological model SWAT to simulate and analyze the runoff variation according to the variations of land utilization and forest coverage, hoping to offer theoretical foundations to the construction of forest coverage and the regulation of water resource in the forest region of the upstream area. The main research achievements are as follow: (1) During the study period, there is a tendency in the upstream area of Shiyang River that the area of grassland increases, the area of shrubwood first increases and then decreases, and the area of coniferous forest, shrubwood and water decreases. The upstream area of Shiyang River has a tendency of the grassland, farmland, settlement place and bare rocks increasing while the forest and flood land decreasing. Among the six kinds of land-use types—the grassland, the woodland, the plowland, the glacier, snows and the fell-field, the grassland takes up the largest area, which is above67%of the whole drainage area The shrubwood has an obvious tendency to increase, but the glacier and snows, the grassland and the arbor frost has reduced. The growing rates of farmland and water area are within one percentage. The conversion of land utilization has not showed the evident regularity. The grassland’s rate of change is minimum, only3.46%; and the following ones are water area, forest, ice and snows, shrub and farmland. The maximum one is bare land, of which the changing rate reaches up to282.64%. The sTab.ility of grassland landscape is the highest, while the bare land changes most, turning into the least sTab.le one among the landscape types in the upstream area. Analyzing from the changing pattern of the patch, the result shows that the landscape sTab.ility of bare land is the highest, the grass ranks second. The following ones are shrubwood, ice and snows, water area, forest and farmland successively. The features of land-use space transfer is that the glacier and snows transfer to bare rocks; the grassland to plowland; the shrubwood to grassland; the water area to shrubwood, grassland and farmland; the flood land to settlement place.(2) From the general view, there was a weak decreasing trend for the runoff flowing away from mountains in the upstream area of Shiyang river basin during1999-2009. As to the average runoff of four rivers, there were drought periods in1999,2000,2001, and2002while in the year2003,2004,2005and2006there were rich precipitation. But the annual runoff slightly declined in two consecutive years (2008-2009) since2007. The precipitation showed a clear increase with the tendency rate of minus0.298(i.e. K=-0.298) from1999to2009as a whole. The rising trend is obvious since the mid of2003. The increasing trend of potential evaporation, with the tendency rate of minus2.206(i.e. K=-2.206). The runoff in the upstream of the Shiyang River gives an obvious response to climate change and the variation of runoff mainly depends on the precipitation; global warming causes the temperature to rise; the melt of the alpine glaciers and snows in the upstream of the Shiyang River basin plays a sTab.le role on the runoff flowing away from mountains.(3) In simulating the runoff of high elevation mountains on the upstream area of Shiyang River, the SWAT model is relatively accurate. According to evaluate simulating results after calibration, it proves to be that the overall correlation coefficient is relatively high, which is higher than0.8and the simulating effect is favorable. It indicates that SWAT model with its good practicability can be more accurate to simulate the runoff of high elevation mountains.(4) In the Huangyang River Basin, the precipitation, the potential evaporation and the volume of runoff are unevenly distributed in terms of time. Much rainfall and evaporation are in July and August while top runoff always comes in July. The precipitation has a significant impact on the runoff; so does the temperature on the evaporation. high evaporation is mainly in the northern low mountain range, because of the strong solar radiation, little precipitation and low forest coverage there; and the runoff is largely affected by the precipitation and shares the same spatial distribution with it.