Biophysical processes of the vegetation activity in central China with monsoon variability in East Asia

We explored the effects of anthropogenic land cover and land use (LCLU) changes on the East Asian summer monsoon (EASM) variability based on comprehensive empirical analyses of correlation, regression, composite, and causation during the recent 34-year period of 1982–2015. The spatial patterns of linear regression trends revealed that the EASM weakened over the land and strengthened over the surrounding ocean, which was led by the regression trend over the second half of the study period, specifically, 1999–2015. The significantly weakened monsoon activities over the land were observed in central China, wherein LCLU transitions from grasslands or croplands to forests have been identified since 1998. A significant negative (positive) correlation between precipitation (vertically integrated moisture divergence and outgoing long-wave radiation) and the normalized difference vegetation index was observed in central China, indicating weaker EASM with enhanced vegetation activity. Linear and non-linear causality analyses supported that the vegetation variability in central China during the pre-monsoon to monsoon seasons causes the summer monsoon variability. The interannual variability of vegetation time-series during 1982–2015 was significantly positively associated with surface net solar radiation, surface heat fluxes, 2 m temperature, and temperatures up to the mid-troposphere in central China. Tropospheric warming induced higher geopotential heights and related anomalies of negative vorticity and descending air in the upper atmosphere over the central China region. Under unfavorable thermodynamic conditions, monsoonal convections were diminished in the monsoon region. Based on the empirical results, we proposed biophysical processes of vegetation activity in central China with EASM variability.