Response Of Vegetation In Mid- And High-latitude Asia To Extreme Climate And Its Simulation Evaluatio

Under the background of global warming,extreme climate events are more frequent and affects the physiological structure and function of terrestrial ecosystems.As the region with the most serious warming,the response of the ecosystem at middle-to-high latitudes in Asia to extreme climate is very complex.Based on the Leaf Area Index(LAI)data obtained by GIMMS and GLASS satellites and multiple sets of reanalysis of air temperature and precipitation data,this study analyzed the response of vegetation to extreme temperature and precipitation at middle-to-high latitudes in Asia,and then evaluated the performance of the CLM4.5-CN model to simulate vegetation responses to climate extremes.Furthermore,based on the model evaluation,combined with the vegetation carbon flux data obtained from multiple sources,the biophysical processes of extreme climate affecting vegetation in the middle and high latitudes of Asia are discussed from a single point scale.The main conclusions are summarized as follows:(1)From 1982 to 2016,the area with the maximum(minimum)LAI increased(decreased)over time,consistent with the trend of increasing LAI in mid to high latitudes of Asia caused by global warming.Extreme hot generally promoted forest growth in Central Siberia and northeastern China,and inhibited the growth of grasslands and sparse vegetation in the northern Mongolian Plateau.Extreme cold had positive effects on sparse vegetation growth in central Kazakhstan.Extreme wet promoted the vegetation growth in Kazakhstan and Mongolia Plateau but inhibited the growth forest land between 50°N and 60°N.Among the compound extreme climate events,hot-and-dry events occurred most frequently,which promoted the growth of forest land in southern Central Siberia.(2)The CLM4.5-CN model can simulate the time trend and spatial distribution of the maximum and minimum LAI values.However,in the central part of the Central Siberian and the southern part of the East Siberian,the simulated maximum LAI appeared later than observed maximum LAI.In high latitudes and southeast of Central Siberia,the simulated minimum LAI appeared later than observed minimum LAI.In terms of the spatial distribution of the frequency of extreme climate events and their impacts on different vegetation types in different regions,the simulation results were consistent with the observational results.However,the effects of extreme hot and dry on vegetation were underestimated at high latitudes.(3)Extreme heat enhanced transpiration of grassland and reduced soil moisture which inhibited the growth of grassland.However,extreme hot enhanced the photosynthesis of forestland.Extreme cold alleviates the heat stress of grassland,weakens the transpiration and respiration of grassland,and reduces the consumption of organic matter,which is conducive to its growth.However,extreme cold can weaken the carbon sink function of forest land by inhibiting photosynthesis.Extreme wet promotes the growth of grassland by alleviating its water stress.Drought accompanied by high temperature obviously promoted the respiration carbon emission of grassland,which was not conducive to the accumulation of organic matter.Compared with extreme precipitation,forest land is more sensitive to extreme temperature,while grassland is sensitive to extreme temperatures and precipitation.In general,forest showed adaptability to high temperature and drought at middle-to-high latitudes in Asia during 1982-2016,and cold and wet climate were the main factors limiting its growth.The CLM4.5-CN model underestimated the adaptability of forest to high temperature and drought in this region.Sparse vegetation and grassland showed opposite response characteristics to forestland,which was related to the climate background.The results of this study may predict the further increase of vegetation cover at middle-to-high latitudes in Asia under the condition of continued warming in the future.