Analysis Of Spatio-temporal Variation Of Vegetation Ecosystem In Beiluo River Basin In The Context Of Climate Change

In today's society,climate change is an important issue that is of general concern,which seriously threatens the balanced development of natural ecosystems and socioeconomy,especially for environmentally fragile areas.The Beiluo River Basin is located on the Loess Plateau,with complex and varied topography,diverse vegetation types,lack of water resources and serious soil erosion.In recent years,vegetation ecosystems show structural and functional degradation under the influence of climate change and human activities,soil erosion increased in the watershed,the ecological environment changed rapidly,and the ecological protection faced severe challenges.Therefore,it is of great theoretical and practical significance to explore the response of vegetation ecosystems to climate change in the Beiluo River Basin under the background of climate change.This paper takes the Beiluo River Basin as the study area,and takes the MODIS data between 2000 and 2014 and the daily meteorological data of the 10 meteorological stations in the basin as the data source.The spatial and temporal distribution patterns of temperature,precipitation and solar radiation were analyzed.And the temporal and spatial distribution and variation characteristics of surface evapotranspiration,net primary productivity and water use efficiency of vegetation ecosystem were studied.And on this basis,the response relationship of vegetation ecosystem to climate change was discussed.The main conclusions are as follows:(1)The average temperature in the Beiluo River Basin from 2000 to 2014 showed asymmetric characteristics.The average temperature dropped from 2000 to 2014,with a tendency of-0.15?/10 a.The average temperature in the growing season is increasing,and the average temperature of the four seasons is increasing in the autumn,and the other three seasons are decreasing.The change of autumn and winter is the most obvious;The annual precipitation is increasing in most areas,and the area of increasing trend is 88.21%.The average rainfall in the growing season also shows an increasing trend.In the seasons,the precipitation in spring,autumn and winter is reduced,and in summer it's increased;The annual average solar radiation exhibits a gradual banding,increasing gradually from southeast to northwest,and most areas showed a decreasing trend.Solar radiation in the growing season also showed a decreasing trend,and the area of the reduced area accounted for 95.29%,more significant than the annual change.(2)The change of ET in the Beiluo River Basin from 2000 to 2014 is obvious,and the largest amount of evapotranspiration occurred in 2002-2004,2012 and 2014.During the year,ET was a single peak distribution pattern,and changes obviously with seasons,mainly concentrating in the period from May to September.The annual NPP distribution shows a decreasing trend from south to north as a whole.During the past 15 years,the net primary productivity of vegetation in the Beiluo River Basin fluctuates with the increase of the trend.The fluctuation range is 147.39 gC·m-2·a-1,and the increasing trend is 5.6 gC·m-2·a-1;The water use efficiency of vegetation showed a fluctuating increase trend.The fluctuation range of water use efficiency was 0.6-0.82 gC·mm-1·m-2 in 15 years,but the trend of improvement was not obvious.And most of the areas were relatively stable status.(3)The average annual temperature of the Beiluo River Basin was slightly decreased from 2000 to 2014,the average temperature in summer and spring as the same.The annual precipitation,the seasonal precipitation and the summer precipitation all show an increasing trend.The annual average solar radiation exhibits a gradual banding,increasing gradually from southeast to northwest.The solar radiation in most of the basin is decreasing,and the solar radiation in summer and growing season also shows a decreasing trend.However,the average annual WUE showed a steady trend,indicating that the temperature of the watershed,solar radiation to a certain extent,has been higher than the normal growth of vegetation needs.And currently,temperature and solar radiation are not the limiting factor to the vegetation ecosystem in this watershed.The correlation between annual WUE and annual solar radiation and annual mean temperature is affected significantly by summer solar radiation.Summer solar radiation and average temperature have a greater contribution to vegetation year WUE;The annual WUE of the basin has a strong correlation with the precipitation in different periods,and the impact of each period on the annual WUE is very important.However the summer precipitation has the greatest impact on the Beiluo River Basin.And the correlation between the annual WUE and the precipitation is the correlation between the summer precipitation and the annual WUE.(4)The average temperature in the Beiluo River Basin is slightly decreasing from 2000 to 2014,and the annual precipitation shows an increasing trend,and the annual solar radiation is decreasing,while the annual WUE shows a steady increase trend.It is found that the temperature and solar radiation are not the limitation of the area,and the precipitation is the main factor that restrict the vegetation ecosystem in the basin.The correlation between annual WUE and meteorological factors in different periods shows that the correlation between annual WUE and climatic factors in summer is the strongest.Therefore,the summer precipitation is the most important factor affecting the vegetation ecosystem in the Beiluo River Basin.How to supply vegetation water according to the summer water demand of the vegetation ecosystem in the watershed is the focus of the management work in this area,which will seriously affect the growth of vegetation ecosystem,and thus affect the region's ecological environment and socioeconomic development.