| In recent years,human activities have further accelerated the rate of changes in natural ecological environment.The global average temperature has risen by 0.85 °C.High latitude and high elevation areas in the northern hemisphere have been particularly heated.Climate warming has had a significant impact on terrestrial ecosystems.Surface albedo is the key factor that restricts the radiation energy budget of land surface,and it is also the key physical parameter affecting the balance of surface radiation energy.It plays an important role in regional temperature change and energy balance.Its temporal and spatial variation characteristics have become a scientific research,the focus of the content plays a key role in the simulation of climate evolution.The Qinghai-Tibet Plateau has a vast area and a special geographical position.It is an "amplifier" and a "regulator" for global changes.Accurately assessing the temporal and spatial variation characteristics of surface albedo on the Tibetan Plateau and its driving factors are of great significance for correctly understanding the feedback relationship in the process of synergy between land surface ecological processes and regional energy changes,and verifying and improving the land surface process model.This paper is based on MODIS Albedo(MCD43A3)from 2000-2016,MODIS NDVI(MOD13A3),DEM and meteorological data(2000-2015),using MRT,SPSS,Arcgis,Sigmaplot and Python tools,to grow grassland in Qinghai-Tibet Plateau.This paper studies the average surface albedo,vegetation cover and the temporal and spatial variation of temperature and precipitation in the grassland growing season in the Qinghai-Tibet Plateau,and discussed the temporal and spatial responses of surface albedo to vegetation cover,temperature and precipitation.Taking 1000 m as the ladder,studied the characteristics of the elevation gradients of the surface albedo and vegetation cover,temperature and precipitation changes,and disscussed surface albedo changes on the other three factors in different growth gradients on the Qinghai-Tibet Plateau.The main conclusions of this paper are as follows:(1)The surface albedo of the grassland growing season in the Qinghai-Tibet Plateau decreased significantly from 2000 to 2016,but it has obvious spatial differences.The albedo of the grassland in the Qinghai-Tibet Plateau showed a significant downward trend with a rate of change of 0.2%/10 a.The surface albedo rate of lowland meadows and alpine grassland decreased by 0.2%/10 a,and the alpine grassland and alpine desert steppe decreased by 0.04%/10 a and 0.0007%/10 a,respectively.The average surface albedo was decreasing from northwest to southeast.The area where the surface albedo is basically unchanged accounts for 83.39%,significantly increase and decrease account for 3.52% and 13.09%,respectively.May has the fastest rate of change and is most sensitive to the response to global change.The albedo has a decreasing trend under different altitude gradients.Surface albedo at different altitudes showed a increasing trend,low altitude area change rate is higher.(2)The NDVI of vegetation in the grassland growing season of the Qinghai-Tibet Plateau increased significantly from 2000 to 2016,but it has obvious spatial differences.The NDVI of the grassland growing season in the Qinghai-Tibet Plateau showed a significant upward trend with a rate of change of 0.7%/10 a.The NDVI rising rate of alpine meadow and alpine grassland is 0.6%/10 a,and the rising rate of alpine desert steppe and lowland meadow is 0.8%/10 a and 1.6%/10 a,respectively.The average vegetation NDVI is increasing from northwest to southeast.The area where NDVI is basically unchanged accounts for 74.59%,significantly increase and decrease account for 20.77% and 4.64%,respectively.The rate of change in May was the fastest,and the trend of the early-greening period was greater than that in the browning stage.The NDVI increased first and then decreased and finally increased with altitude gradient.NDVI at different altitudes showed an increased trend,low altitude area change rate is higher.(3)Increased average temperature and precipitation in the grassland growing season of the Qinghai-Tibet Plateau from 2000 to 2015.The spatial distribution of temperature and precipitation in the growing season of the Qinghai-Tibet Plateau is characterized by “decreases from southeast to northwest”.And temperature and precipitation have increased over the past 16 years,with rates of change of 0.29°C/10 a and 8.48 mm/10 a,respectively.The temperature of the grassland in the Qinghai-Tibet Plateau increased linearly with altitude,and the vertical decline rate was different at different altitudes.The vertical decline rate was 5.6°C/100 m at <4000m,and the vertical decline rate was 2.3?/100 m at >4000m.The precipitation decreased first and then increased with the increase of altitude.The high-altitude temperature increase of grassland in Qinghai-Tibet Plateau is stronger than that of low-altitude,and the growth rate of low-altitude precipitation is greater than that of high-altitude.The southern and southeastern parts of the study area are warm and dry,and the southwestern and northeastern parts are cold and humid.(4)The albedo of the grassland growing season in the Qinghai-Tibet Plateau is significantly correlated with vegetation NDVI.The surface albedo with vegetation NDVI of the grassland in the Qinghai-Tibet Plateau was negatively correlated and positive correlation area was 71.18% and 28.82%,respectively.There was a negative correlation between NDVI and surface albedo in alpine grassland,alpine meadow,alpine desert steppe and lowland meadow,and the correlation coefficients were-0.77,-0.27,-0.39,-0.24,respectively.The correlation between the low-value covered areas is stronger than the high-value covered areas.The albedo with the NDVI of different altitudes was negatively correlated.The correlation of <3000m area increased with the elevation,and the correlation of >3000m decreased with the elevation.(5)The surface albedo with temperature of the grassland in the Qinghai-Tibet Plateau was negatively correlated and positive correlation area was 45.76% and 54.24%,respectively;the surface albedo with precipitation of the grassland in the Qinghai-Tibet Plateau was negatively correlated and positive correlation area was 73.07% and 26.93%,respectively.The correlation with precipitation is stronger than the correlation of temperature,but the correlation is weak.At the beginning of the growing season(May and June),the surface albedo has a strong correlation with the temperature during the same period;the medium-term(July and August)has a one-month lag effect with precipitation;the end of the growing season(September)is affected by temperature and precipitation,but the correlation between is weak.There are significant differences in the main climate driving factors for the change of surface albedo in the growing season of grassland in Qinghai-Tibet Plateau.<2000m area is mainly negatively correlated with temperature;2000-4000 m and 5000-6000 m are mainly negatively correlated with precipitation;4000-5000 m and >6000m are affected by temperature and precipitation,and the correlation between them is weak. |
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