Quantitative Discrimination Of The Effects Of Human Activities And Climate On Vegetation Growth In The Tibetan Plateau Based On Remote Sensing

Quantitatively distinguishing the impact of human activities and climate on vegetation growth is the key to scientifically planning vegetation management measures,which will be of great significance to ecological environment protection and vegetation construction.Previous studies have employed the residual trend method（RESTREND）and remote sensing data to address this issue.However,the mathematical relationships between climate and remote sensing vegetation index under RESTREND are variable and not comprehensively described due to temporal effects of climate factors on vegetation growth.In this study,the MODIS normalized difference vegetation index（NDVI）data and climate data of the Tibetan Plateau from2000 to 2019 were obtained,and the variation characteristics of regional vegetation growth and climate factors of the Tibetan Plateau in recent 20 years were analyzed;By establishing four different temporal effects of climate on vegetation growth:no temporal effect（No）,temporal lag effect（Lag）,temporal accumulation effect（Acc）and considering both temporal lag and accumulation effects（Lagacc）,the multiple linear regression equations between annual maximum NDVI and monthly temperature and precipitation were constructed to analyze the temporal effects of climate factors on vegetation growth in the Tibetan Plateau,the importance of considering Lagacc effect was clarified;The correlation between vegetation and temperature and precipitation under four temporal effects was analyzed by partial correlation analysis,and the dominant climatic factor affecting vegetation growth in this area was discussed;Based on different temporal effects,the influence and contribution rate of human activities on vegetation growth in Tibetan Plateau were analyzed.The results can provide theoretical support for understanding the relationship between vegetation and climate,and provide scientific basis for eco-environmental protection and vegetation construction in the Tibetan Plateau.The main conclusions are as follows:（1）The Tibetan Plateau has shown a"warm and humid"trend in the past two decades.In terms of spatial distribution,the temperature and precipitation show a gradual decreasing trend from southeast to northwest.The regions with significant annual temperature increase are mainly distributed in the northeast,west and central south of the Tibetan Plateau,accounting for 22.59%of the total area of the Tibetan Plateau,with an average rate of 0.03°C/a;The areas with significant increase in annual precipitation are mainly distributed in the northeast of the Tibetan Plateau,accounting for 9.94%of the total area of the Tibetan Plateau,with an average increase rate of 5.62 mm/a.（2）From 2000 to 2019,NDVI showed an increasing trend in 75.6%of the Tibetan Plateau,and the overall vegetation restoration was in good condition.The areas with significant increase in NDVI were mainly distributed in the northern and southern edge of the Tibetan Plateau,accounting for 20.28%of the area of the whole region.The areas with significant decrease in NDVI were scattered in the middle of the Tibetan Plateau,accounting for 1.30%of the area of the whole region.（3）Under the Lagacc effect,the temperature exhibited 1.60±0.13 months lag and4.56±0.28 months accumulation on vegetation growth over entire the Tibetan Plateau,whereas the precipitation exhibited 1.57±0.16 months lag and 4.99±0.31 months accumulation.Furthermore,the grids affected by the combined temporal lag and accumulation effects of climatic factors accounted for 43.42～45.78%of the total grids.The temporal effects of climate factors on vegetation growth were largely affected by the comprehensive temporal effects of climate.Compared with No effect,considering Lagacc effect can increase the interpretation of climate to vegetation growth by4%～18%.（4）The partial correlation between NDVI and precipitation is higher than that between NDVI and temperature.Under the Lagacc effect,the partial correlation coefficient between NDVI and precipitation is 0.25.The regions dominated by precipitation are mainly distributed in the northeast and southwest of the Tibetan Plateau,accounting for about 40.1%;The partial correlation coefficient between NDVI and temperature is 0.08.Temperature dominated vegetation growth is concentrated in the central and southeast of the Tibetan Plateau,accounting for about29.7%.（5）Lagacc effect exhibited the smallest influence area,the lowest influence degree and the lowest contribution rate of human activities on vegetation growth.Under the Lagacc effect,the area where human activities have a positive impact on vegetation growth accounts for 11.6%,and the impact rate is 22.2%×10^-4,mainly distributed in the north and southeast of the Tibetan Plateau.The proportion and rate of negative effects of human activities on vegetation growth were 1.3%and 24.0×10^-4,respectively,mainly distributed in the middle of the Tibetan Plateau.In addition,in the regions with positive and negative effects of human activities,the average contribution of human activities to vegetation growth is 54.5%and 55.5%,respectively.