Satellite observed reversal in trends of tropical and subtropical water availability

Understanding the spatially and temporally non-uniform water availability trends is key to assess changes of tropical and subtropical ecosystem productivity. However, their detailed spatial-temporal patterns and the relative role of local to the overall trend are not well known. This study provides a comprehensive investigation in characteristics of the time-varying water availability trend using the ensemble empirical mode decomposition (EEMD) method based on state-of-the-art satellite microwave observation derived microwave integrated drought index (MIDI) from 1998 to 2016. The results indicated an increased area with wetting trend since 1998, and the overall water availability reversed a drying tendency to a wetting trend around 2005. Also, the Northern Hemisphere became wetter and the Southern Hemisphere became dryer in 2016, demonstrating a transformation of favorable climate from the Southern Hemisphere to the Northern Hemisphere. Spatial patterns of the trend shape determined spatial distributions of the trend contributions, showing an opposite contribution between subtropics and tropics. Additionally, tropical rainforests and shrublands governed the overall trend reversely. This analysis helps to understand the non-uniform patterns of water availability trend and related ecosystem productivity over tropics and subtropics.