Responses Of Climatic Variability And Land Use/Cover Change To Rimofnn Le’an River Watershed

Climatic variability and land use/cover change(LUCC) have been commonly recognized as two major drivers for streamflow variations at a watershed scale. However, many studies have focused on the influence of climate factors on water resources, rarely with studies on effects of land use/cover change, Actually, LUCC have cumulative impacts on the regional water resources, which has aroused extensive concern in academia. In past decades, the occurrence of these phenomena such as water level in low innovation, the extension of low water level duration, and frequency extreme floods and droughts have caused widespread concern in the community. There was a debate on whether climate variability or LUCC is major driver for streamflow variation of Poyang lake. In this study, the Le’an Watershed as the one of the main tributaries of Poyang Lake was selected, with long-term date(1954-2012) on climate and hydrology. An integrated methodology combining advanced statistical methods(Sensitivity-based approach)with theoretical mode(Tomer-Schilling framework) was used to conduct statistical and quantitative contributions, in order to provide basic data for scientific assessment of land use change to regional water resources. The main results were as follows:(1) Through the analysis of the climatic factors over the whole study period,we found the annual mean temperature increased significantly(P<0.01), in the past decades, the drought days was increasing, especially in the 2003(56d), 2004(57d) and 2007(81d) year; on the contrary, it was found that precipitation has a weaken increase, besides,the average intensity and frequency of storm rainfall were increased.(2) Through the Mann-Kendall mutation point test, two breakpoints in the runoff(year 1985 and year 2003) were detected in the Le’an River Watershed(P<0.01),which proved large-scale land use / cover change and climatic variability had maked significant changes to streamflow in past decades.(3) From 1985 to 2005 LUCC included:Forests and construction land were increased by 30.65 km2 and 17.94 km2, grassland and cultivated land reduced by 34.13 km2 and 13.70 km2, water area and unused land area changed little; NDVI from 0.2950(1985) reduced to 0.1302(1995) then increased to 0.2645(2005). The results showed that the policy of returning farmland to forest policy had positive effect on vegetation recovery in the basin, and the vegetation cover was gradually restored and improved.(4) By using the Sensitivity-based approach and Tomer-Schilling framework, we concluded that in period of 1986 to 2003, climatic variability(66.15%)was more dominat than LUCC(33.85%);however, 2004 to2012, LUCC(77.60%)was more dominat than climatic variability(22.40%).(5) Climatic variability and LUCC produced joint positive effects, both of which were cumulative runoff or diminish the role of runoff.(6) LUCC and climatic variability performed the different effects on streamflow in different period of Le’an River basin,all that mostly depended on the degree of response of streamflow.