The Spatio-temporal Evolution Of Water Conservation In Qinling Mountains And Its Response To Climate

The Qinling Mountains cross the east and west of China yet,and is a significant natural defense and water-saving area in the middle of our country,there is a lack of in-depth research on the ecological function service of Qinling Mountains water retention.This paper was focused on the research point of water conservation function in the Qinling Mountains core area.Therefore,this article draws on relevant knowledge of ecosystem theory,and chooses to use InVEST model,modified Penman-Monteith model and related spatial analysis methods,etc.This paper explored the temporal-spatial variation trend and dynamic development of water-saving of ecological functions in the Qinling Mountains from 1980 to2018 by comprehensive use of multi-types data sets to analysis the rule.In addition,the linkage between impact factors and water conservation was preliminarily analyzed,and the response of water conservation to climate was in-depth assessed at different scales,above which is aimed at the simulation prediction of water conservation in the Qinling Mountains for different scenarios in the future,with a view to providing reference for water conservation in the Qinling Mountains.The main conclusions of this research can be divided into the following aspects:(1)From 1980 to 2018,the annual mean temperature and evapotranspiration in the Qinling Mountains increased,while the annual rainfall decreased,with a changing trend of0.37?/10a,10.64mm/10a and-17.03mm/10a,respectively.And the annual mean values of these three elements were 12.76?,875.89mm and 840.70mm,respectively.Spatially,the distribution patterns of precipitation and temperature are roughly the same,both decreasing from south to north of the Qinling Mountains,while the distribution of evapotranspiration values corresponds to the distribution of altitude.(2)Judging from the characteristics of land use changes in the Qinling Mountains from 1980to 2018.The main types of land use or area reduction are forest land and arable land,which have decreased by 65.68 km~2 and 12.38 km~2,respectively.But the area of grassland,waters and so on shows to increase,the distribution of land increased by 38.12km~2,11.75km~2 and28.16km~2,respectively.From the age change of land use type,we found that,the increase of cultivated land was accompanied by the decline of forest land and grassland from the 1980s to the 2010s.In other words,the variation trend of cultivated land was opposite to that of forest land and grassland.(3)From 1980 to 2018,the multi-year average water conservation per unit area in the Qinling Mountains fluctuated between 0 and 1140.69 mm.And the water conservation depth and water conservation total were 51.84 mm,30.12×10~8 m~3,respectively.Generally,in recent 39years,the overall trend of water conservation has been-2.14×10~8m~3/10a,showing a slow decline.In addition,due to the emergence of extreme precipitation during this period,the water conservation in the Qinling Mountains experienced three major abrupt changes in1981,1983,and 1997,respectively.Spatial distribution pattern of water retention in Qinling Mountains is shown as high in the south and east,and north and west are low.More specifically,the lower reaches of the Jialing River basin and the high mountain ridge areas in the central and western Qinling Mountains are high value areas of water conservation,while the Danjiang basin and adjacent small watersheds in Shangluo City are low value areas of water conservation.From the perspective of the first-level basins in the Qinling Mountains,the water retention in descending order is 16.40×10~8m~3 in the Hanjiang River Basin,4.94×10~8m~3 in the Weihe River Basin,4.15×10~8m~3 in the Jialing River Basin,2.93×10~8m~3in the Danjiang River Basin,and 1.54×10~8m~3 in the Luohe River Basin.(4)The influence of topographical factors on water conservation is firstly that the higher the DEM,the higher the water conservation,and the change trend is 16.8mm/km.Secondly,as the per degree of slope increased,water conservation decreased by 0.72 mm.From the perspective of the influence of climatic factors on water conservation,the change trend is3.91mm/?,and the correlation is negatively correlated with altitude.Besides,water conservation is also positively interrelated to precipitation,that is,for every 10mm increase in rainfall,water conservation increases by 2.67mm.It is negatively correlated with evapotranspiration.When evapotranspiration increases by 10mm,water conservation decreases by 1.96mm.The impact of land use factors on water conservation is mainly due to differences in water conservation of different land use types.In this study,forest land(15.09×10~8m~3)>grassland(9.43×10~8m~3)>farmland(5.53×10~8m~3)>Construction land(0.04×10~8m~3)>Unused land(0.01×10~8m~3).Among them,the water retention of forest land and grassland accounted for 81.41%of the study area,becoming the main contributor.(5)Under the extreme precipitation conditions,the water conservation amount changed significantly.Compared with the annual average,the water retention in wet years is 2.36times,while in dry years is only 25.93%.The effect of extreme rainfall on water conservation is 59.46mm higher in wet year than normal year,and the dry year is 18.29 mm,less than the normal year.In addition,according to scenario simulations,we got a result that climate variation is the primary impact factor of water conservation,and the simulation shows that the average water conservation in the Qinling Mountains in the next decade is 31.48×10~8m~3,which is an increase of 1.36×10~8m~3 compared with the average water conservation over the years from 1908 to 2018.