Climate And Land Use Change And Its Impacts On Runoff In Ningxia Yellow River Valley

Ningxia Hui Autonomous Region, which is located in the arid and semi-arid area in Northwest of China, is one of the mostly lacking water areas. And water has becoming one of the most important restriction factors to the social and economic development in Ningxia. While, the climate and land use change can largely influence the hydrological conditions through change the precipitation pattern and water use pattern. Therefore, Ningxia Yellow River Valley was chose as study area, and with the help of RS and GIS to analyze climate and land use changes from 1980s to 2010s.Then, future change scenarios of climate and land use were set base on historical data. After this, the distributed hydrologic model of SWAT was used to simulate runoff response to the future change scenarios of climate and land use in a typical basin of Ningxia Yellow River Valley. Main conclusions are as follows:(1)Ningxia Yellow River Valley was departed as five regions (northern, western, central, eastern and southern) depend on climate divisions of Ningxia Hui Autonomous Region and the patial distribution pattern of precipitation and temperature. The precipitation change analysis showed that the annual precipitation of northern region and eastern region were increase from 1980 to 2010, while western region, central region and southern region were decrease during 1980 to 2010, and all of these trends had no significant change. The temperature change analysis showed that the annual mean temperature of all regions had significant increase from 1980 to 2010 besides eastern region, and the change variations from large to small were southern, northern, western, central and eastern. Besides five regions, the climate change of the whole valley was analyzed, the results showed that the precipitation was decrease and temperature was increase in period of 1980 to 2010. Combine the change of precipitation and temperature from 1980 to 2010, we can know that the climate change trend of western region, central region, southern region and the whole valley were becoming warming and drying, the northern and eastern regions were becoming warming and moisture.(2) The dominated land use types were grassland and farmland during the period 1985 to 2010. The area of woodland, water, building land, and farmland increased more or less, and the grassland and unused land decreased. The distribution of each land use type did not change from 1985 to 2010 in Ningxia Yellow River Valley. And the transfer matrix showed that the significant changes were grassland to farmland, unused land to grassland and farmland, and farmland change to building land and grassland. The distribution of the gravity centers of land use types was all at Wuzhong city or the edge of Wuzhong. The gravity centers change of different land use types were variation from 1985 to 2010.And the water and unused land had more obviously change than other land use types. There were four hot spots of dynamic changes in land use from 1985 to 2000 and they distributed in the northern and central area. While there were nine hot spots of dynamic changes in land use from 2000 to 2010 and they distributed in a larger range in the northern and central area.(3) The landscape fragmentation was analyzed by effective mesh size{mef), which is a new and better landscape index to analyze landscape fragmentation. The quantity analysis show that the degree of landscape fragmentation of the whole valley in 2010 has strengthened compared with 1985.Except the Yellow River irrigation areas, and the landscape fragmentation of other six subbasins were increasing too. The spatial heterogeneity of landscape fragmentation show that the area of high landscape fragmentation value was obviously larger than low value area both in 1985 and 2010, and it mostly distributed in Qingshui River basin, Yanchi and so on. And the high landscape fragmentation value area showed an obvious upward tendency in scope and degree compared 2010 with 1985.(4) Qingshui River basin was chosen to analyze the hydrology of Ningxia Yellow River Valley. Through the analysis and statistics of soil, climate, land use and DEM to build SWAT database, then built SWAT model of Qingshui River basin. The model showed Qingshui River basin was subdivided into 28 subbasins and 120 hydrological response units. Using measured monthly runoff data of the year 2000 to 2011 of Hanfuwan station and Quanyanshan station to calibrate and validate the SWAT model.The parameter sensitivity analysis results show that CN2 (Run off Curve Number Method), CH_N2 (Manning’s "n" value for the main channel), CANMX (Maximum canopy storage), ALPHA_BNK (Baseflow alpha factor for bank storage) and SOL_AWC (Available water capacity of the soil layer) were the main parameters to influence runoff. And all the results of R2 and the ENS coefficient from calibration and validation of Hanfuwan station and Quanyanshan station were acceptable and satisfied. The SWAT model can be used to simulate runoff of Qingshui River basin.(5)Built future climate and land use change scenarios based on historical trend, and simulated the future runoff of Qingshui River in 2020 with SWAT model. The results were as follows:①The runoff effects under precipitation change is larger than temperature change. And the precipitation and temperature combination scenario has the largest impact on runoff.②Three scenarios of land use in 2020 would obviously increase the runoff of Qingshui River basin. The Natural development scenario has the largest impacts, the second is Ecological protection scenario, and then is Planning scenario. ③The runoff would decrease in the likeliest scenarios. The scenario which combines Planning land use, precipitation and temperature has the largest impact to decrease runoff, and Natural development land use combine with precipitation and temperature has the smallest influence on runoff.(6) The increase of slope farmland and ecological land would help to increase runoff. But slope farmland courses a lot of ecological problems. So, the right way to increase runoff of Qinghsui River basin is accelerate the construction of woodland and water, and turn the slope farmland to forest and grass at the same time. On the other hand, ecological land can adjust the climate of small area to increase the runoff indirectly.