Driving Factors Analysis And Dynamic Prediction Of Alpine Grassland Degradation And Restoration On The Tibetan Plateau Based On Remote Sensing

Alpine grassland in Tibetan Plateau has been degraded due to the effect of climate change and disturbance of human activities,which has caused a series of ecological,economic,and social problems.It is vital to scientifically evaluate the degradation and restoration of grassland and monitor the health of grassland in time,which may advance the sustainable management of grassland and ecological environment protection.It is also a hot topic for the government,researchers,and the public.In this study,through using the CASA model,the alpine grassland net primary productivity（NPP）was calculated from 1982 to 2015 based on meteorological data and NDVI products of GIMMS in the Tibetan Plateau.Then,the contribution of climate change and human activities to grassland degradation and restoration was analyzed through the Miami model.Finally,the Second-Generation Beijing Climate Centre Climate System Model（BCC-CSM2-MR）was used to predict the impacts of climate change on alpine grassland degradation and restoration in the Tibetan Plateau under different greenhouse gas emissions scenarios（ssp126,ssp245,ssp370,and ssp585）from 2021 to 2100.The main conclusions are as follows:（1）From 1982 to 2015,the spatial distribution of precipitation,temperature,and NPP in the southeast of Tibetan Plateau was higher than that in the northwest,and the precipitation,temperature,and NPP in the growing season increased significantly,compared with the annual average value.Additionally,among different grassland types,the alpine meadow had the fastest recovery rate,followed by alpine grassland,and alpine desert grassland had the slowest recovery rate.Moreover,the response rate of NPP to growing season precipitation is faster than that of mean annual precipitation.Conversely,the response rate of NPP to mean annual temperature is faster than that of growing season temperature.Besides,the response patterns of NPP to precipitation and temperature showed differences in various grassland types.Specifically,the alpine meadow showed the highest sensibility,followed by the alpine steppe,and finally the alpine desert steppe.（2）From 1982 to 2015,the climate-dominated NPP(NPP_climate)and human-dominated NPP(NPP_human)of alpine grassland in the Tibetan Plateau showed recovery trends,and the area of grassland restoration was larger than that of grassland degradation.Among the dominant factors leading to grassland degradation,climate change accounted for 75.1%,human activities accounted for 24.0%,and combined contribution was 0.9%,respectively.Also,among the dominant factors of grassland restoration,human activities accounted for 60.7%,climate change accounted for19.7%,and combined contribution was 19.6%,respectively.Significantly,the dominant factors and contributions of grassland degradation/restoration are different among different grassland types.However,the overall result is that climate change dominates grassland degradation,and human activities dominate grassland restoration.（3）The spatial distribution patterns of NPP_climateof four carbon emission scenarios decreased from southeast to the northwest along a gradient under the BCC-CSM2-MR model,from 2021 to 2100.The data characteristics show that NPP_climatein ssp585 and ssp370 scenarios may gradually increase in the next 80 years,and the average value may increase from below 500 g C m^-2yr^-1to above 500 g C m^-2yr^-1.Furthermore,in ssp585 scenario,the degradation area of the alpine meadow was the smallest and the restoration area was the largest;in ssp245 scenario,the degradation area of alpine grassland was the smallest and the restoration area was the largest;in ssp245 scenario,the degradation area of alpine desert grassland was the smallest and the restoration area was the largest.