Response On Eco-hydrology In Beichuan River Basin

In recent years,with the rapid development of social economy in Beichuan River Basin.The regional water resources shortage,water ecological security and other problems and the contradiction between supply and demand of water resources are increasingly serious which effected the healthy and the stable development of regional social economy.This study takes Beichuan River Basin as an example,is on the basis of meteorological and hydrological data,land use,geological and geomorphic data from 1961 to 2017 in different spatial scales and on the change of land use to analyze the landscape pattern change and discuss the driving factors of hydrological process in the basin,and then study the climate change and human activities,further analyze the relationship between forest vegetation and runoff.This study aims to provide theoretical basis and scientific means for improving regional water resources and ecological environment security.The main results of this study are as follows:(1)During the study period,the precipitation,temperature and potential evapotranspiration all increased,with uneven seasonal distribution and the same period of rainfall and heat;the temperature and potential evapotranspiration of the basin increased gradually from northwest to Southeast,and the precipitation tended to decrease.The land use pattern is dominated by forest,grassland and cropland types.In 1990,2000 and 2010,the area of forest and grassland increased and cropland decreased.Meanwhile,the water area of Xiamen sub basin increased significantly,and the scale of cropland conversion into forest and grassland in different sub basins within the basin also varied.The landscape diversity and complexity of the basin increased,and the degree of aggregation increased the connection between landscapes is close,the connection between cropland patches tends to be loose,and the internal aggregation of forest and grassland patches is strengthened.(2)During the study period from 1961 to 2017,the annual average runoff of Beichuan River Basin presented a declining trend,and the runoff changed abruptly in 1972 and 1989.The annual average runoff of the upstream of the basin was larger than that of the downstream.In the sub basin,the runoff in Chaoyang changed only in 1989,and the runoff in Xiamen fluctuated violently for many times.The sensitivity analysis of runoff showed that every 10% increase in precipitation and potential evapotranspiration would lead to a 17.9% increase and 7.9% decrease in runoff within the basin.The sensitivity coefficient of runoff to precipitation and potential evapotranspiration in chaoyang sub-basin was the highest within the basin.There was a significant negative correlation between the sensitivity coefficient of precipitation and potential evapotranspiration to runoff and the runoff coefficient Q/P,revealing that the drier the area with less precipitation,the more sensitive the runoff was to the change of precipitation and potential evapotranspiration in the basin.(3)The contribution rate of the driving factors affecting the runoff process in Beichuan river basin is mainly land use factor(66.61%),meteorological factor(16.06%),topographic factor(11.57%)and morphological factor(5.77%),and the cumulative contribution rate of forest,grassland and cropland to the multi-year average runoff is more than 60%.In addition,the contribution rate of the multi-year average precipitation to the runoff is also high the results show that the change of forest vegetation and precipitation is the main driving force of runoff change in Beichuan River Basin.(4)Regarding the time point of runoff mutation,the research period can be divided into the base period before the mutation and the change period after the mutation.During the change period,the precipitation,temperature and potential evapotranspiration was increased,and the runoff was decreased.In the process of runoff change,climate change plays an increasing role,while human activities reduce runoff directly and indirectly,which plays a leading role in the basin runoff change with a contribution rate of about 70% within the basin.The human activities affects runoff,the greatest is in Qiaotou while the smallest is in Heilin.(5)Forest vegetation reduces annual runoff.Per 1% increase of forest,grassland and cropland in Beichuan river basin reduces runoff by 1.39 mm,1.26 mm and 1.04 mm respectively.The stronger ability of forest vegetation and the more influence on runoff in warm and humid areas,the less influence on forest vegetation in dry and cold areas.In addition,the increase of forest vegetation regulates regional runoff.The runoff of the basin shows a downward trend and fluctuates significantly in the wet season,while the runoff in the dry season is generally flat,and then stable after a period of increase in 2003.The increase of forest coverage reduces peak flow,delays peak formation time and prolongs flood duration.