Research On The River Base Flow For The Response Characteristics Of The Climate Change And Human Activities In Xilin River Basin

Influenced by the globe climate changes, there are many obvious problems of drought and water shortage such as the betrunking of stream and shrinking of wetland in the eastern grassland region of Inner Mongolia,the grassland desertification degradation is aggravating. Strong disturbance caused by human activities on basin hydrological processes,the surface runoff changed significantly,which restricted socioeconomic development severely and affected the grassland ecological environment directly.As an important part of hydrological characteristic, base flow plays an important role in maintaining water balance and evaluating water resources management.In the background, quantitative analysis of the impact of climate change and human activities on the base flow,it is significant in maintaining benign basin hydrological cycle and sustainable development of grassland ecological environment. The article chooses cold-arid-regions of typical grassland river basin as the research object, to analyze the base flow response to climate changes and human activities. The main results are as follows.(1) Four types of the digital filter method,HYSEP minimum smoothing method and Kalinin method,in total nine kinds of base flow separation methods are used in the study area. The results shows that three iterative digital filtering method (β=0.85)is proved to better applicability, and base flow estimation result is sTablele and reliable. It can be used as optimal base flow separation method in this study area.(2) Analysis of the various meteorological factor variation characteristics and reveal the evolution law of base flow on the Xilin River. The temperature and evaporation overall rise significantly, the higher the temperature,the greater the evaporation. The tendency rate of the ground temperature is 0.426℃/10a,and the tendency rate of the evaporation is 4.322mm/a.The precipitation tendency is decreasing and the tendency rate of the precipitation is-0.446 mm/a,but it is not significant and distributing as "unimodal type".The distribution of base flow in the Xilin River in a year is very uneven. The supply of base flow rely on the meltwater as well as precipitation supplies,and the characteristics of bimodal pattern is obvious. It showed that the average annual base flow was 2.24mm.The base flow droped significantly as a whole.In 60s-70s,the base flow increased slowly.The base flow experienced a process from decrease to increase in 80s-90s, There is a significant reduction in the 21st century. The base flow showed an unsTablele periodic variation about 22 to 32 years,6 to 13 years and 3 to 5 years.There were 5 times on large time scale dry-plantiful alternates alternately,predicting base flow has a tendency to turn to increase.(3) Research on base flow in response to climate changes and human activities by the qualitative analysis methods.There exists extremely noTablele linear ration between the precipitation and base flow. Evaporation and base flow has significant negative correlation. By means of influencing evaporation, the temperature indirectly affect the base flow. The precipitation and base flow relative runoff have the lag effect,in different hydrologic year.the lag time exist the following relations:ample flow years> low flow years> normal flow years.The surface runoff lag time relative to the precipitation in the dry season is obvious longer than in the wet season,however base flow lag time relative to surface runoff in the dry season is slight shorter than in the dry season. The human activities include population explosion, livestock grazing, the unreasonable development and utilization of groundwater, coal mining,water and soil conservation activities and so on effected the base flow.(4) Quantitative decomposition the contribution rate of climate change and human activities on the base flow.With years of inflection point (1979,1991 and 1998)as a boundary, divided 1963-2012 into standard period(T1) and measures period(T2-T4).The contributions of climate to the base flow yield change are 54.15%,30.24% and 43.76% during the period of T2 toT4 respectively,and the contributions of human activities to the base flow yield change are 45.85%、69.76% and 56.24% respectively.In T2 stage,the main driving factor of base flow reduction is climate changes.In T3 and T4 stage,human activities are the dominant factor influenced the base flow changes of the Xilin River Basin.