Spatiotemporal Variation and Influencing Factors of Atmospheric Aerosol in the Middle Region of the Yarlung Zangbo River Basin from 2000 to 2020

Abstract

Based on the aerosol optical depth （AOD） of the MODIS MCD19A2 dataset from 2000 to 2020, combined with meteorological data, land use/land cover data, and socio-economic data, the spatiotemporal distribution of AOD in the middle region of the Yarlung Zangbo River Basin was analyzed using STL and Theil-Sen Median trend estimation and the influence of natural and anthropogenic factors on AOD was revealed using GeoDetector, XGBoost model and SHAP analysis. The results showed that the spatial heterogeneity of AOD in the middle region of the Yarlung Zangbo River Basin was obvious, which was mainly controlled by topography, with high AOD value concentrated in the valley with the altitude lower than 4 300 m. Owing to the precipitation and surface wind speed, the seasonal difference of AOD was obvious, with the highest in winter. From 2000 to 2020, AOD in the middle region of the Yarlung Zangbo River Basin showed an increasing trend, with the annual average AOD rising from 0.008 to 0.012. This increase was especially strong in the valley area, where the AOD was significantly impacted by enhanced anthropogenic activities and the abundance of sand sources of exposed riverbed. Among the factors influencing AOD in the middle region of the Yarlung Zangbo River Basin, the changes in mean annual temperature, mean wind speed, population density, and GDP were positively correlated with the changes in AOD, whereas the changes in precipitation were negatively correlated. In particular, the increase in temperature was the factor that contributed predominantly （61.1%） to the recent changes in AOD.