| As“the driving force”and“the amplifier”for global climate change,the Qinghai-Tibetan Plateau?QTP?plays an essential role in ecosystem security of China and even Asia with the properties of sensitive and fragile to climate change.Accurately assessing aridity-humidity change of the QTP and its influence on vegetation greenness is beneficial to regional animal husbandry development,and it would provide the referenced significance for the construction of ecological safety barrier in China.Based on remote sensing data and meteorological observation data,this study aims to quantify spatio-temporal change of aridity-humidity during 1970-2017 and vegetation greenness since 2003 on the QTP by using Sen's slope estimator,mutation model,correlation analysis and other approach.Then explored the responses of vegetation greenness to aridity-humidity change.The main conclusions are as follows:?1?Continuous wetting on the Qinghai-Tibetan Plateau during 1970-2017.The SPEI of growing season?SPEIgs?on the QTP exhibited a significant increasing trend at the rate of 0.01/yr?p<0.05?,indicating that the QTP tended to undergo continuous wetting during 1970–2017.In contrast,its surrounding area underwent a significant trend shift from an increase to a decrease in SPEIgs around 1984?p<0.05?.Spatially,most of the stations on the QTP were characterized by an increasing trend in SPEIgs,except a small number of stations on the eastern fringe of QTP.Its surrounding area showed strongly different patterns of distribution,most of the stations presented decreasing trend,especially in the southern Gansu,the western Sichuan,and the northwest of Yunnan.The results of the intensity analysis showed that the rate of wet changes was relatively fast in the 1970s–1980s on the QTP,followed by a maintenance phase during 1980s–1990s and 1990s–2000s,and the transition from 2000s to 2010s was associated with wetting.Whether at the regional or site scale,the wetting trend on the QTP is likely to continue in the future,the surrounding area were characterized by a decreasing trend.There were significant difference between ecosystem zones and altitudes in SPEIgs on the QTP,the Qaidam mountain desert area?IID2?and 2000-2500m wetting obviously.?2?Compared MOD-NDVI,MOD-EVI,MYD-NDVI,MYD-EVI vegetation greenness data on the QTP from 2003 to 2018,it can be found that the spatial distribution and spatio-temporal changes of multi-year averages were consistent.Overall,MOD-NDVI is the best one to characterized the vegetation greenness on the QTP.The analysis result depend on MOD-NDVI were shown that monotonic greening trends of the vegetation on the QTP,with local degradation,and the spatial mutation phenomenon is obvious.Regionally,the QTP greening significantly over the past 16years at rate of 12.77?10-4/yr?p<0.01?by Sen's slope estimator and linear regression,which was mainly distributed in northern QTP;and the browning located in alpine region and forest cover areas in southern QTP.According to the BFAST model,the vegetation greenness has experienced abrupt changes in the most ecosystem zones on the QTP,timing of major trend shifts existed around 2010 with greening obviously after abrupt change.On the pixel scale,the vegetation greenness in most areas of the plateau,especially in northern Tibet,has undergone significant shift.There was major difference before and after the abrupt change in greenness between 2012 and 2015,vegetation greening significantly after the abrupt change.?3?Sensitiveness of the responses of vegetation greenness on the QTP to SPEI?r>0.52,p<0.05?.Temporally,the vegetation greenness in July on the QTP showed a significant positive correlation with the long-term SPEI,and the significant positive correlation gradually changed to the short-to-medium term from July to September.Spatially,at June and July,there was a significant positive correlation between greenness and long-term SPEI in the northeast of QTP,and with short-term SPEI in the southwest of QTP.In most regions,the positive correlation was more significant in greenness with short-term SPEI between August and September.Compared with ecosystem zones,the difference in response between greenness and SPEI is more pronounced in different vegetation types.There was a significant positive correlation between steppes greenness and SPEI among all month of the growing season except for May.The correlation between forest and SPEI is weakly negative.In the early and middle growing seasons,the meadow greenness showed a positive correlation with long-term SPEI,while positive correlated with short-to-medium term SPEI in the late growing season. |
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