Evaluation of AMSR-E retrieval by detecting soil moisture decrease following massive dryland re-vegetation in the Loess Plateau, China

Knowledge of soil moisture, however varied in space and time, is critical for planning land use in water-limited drylands. Although satellite observations provide soil moisture instantaneously at large scale, few studies have addressed the application of satellite soil moisture retrieval in dryland areas with changing land use. In this study, we propose a method to evaluate the spatiotemporal variance of satellite retrieval based on the evaluation of soil moisture retrievals from the Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E). The operation period of this instrument (June 2002 to October 2011) covers the re-vegetation of the semi-arid Loess Plateau. Our study found that AMSR-E retrievals posted by the Japanese Aerospace Exploration Agency (JAXA) capture the spatiotemporal variance of soil moisture in the Loess Plateau, as well as the in-situ measured soil moisture decrease following the massive re-vegetation- despite it differing from the in-situ measurement in spatial scale. Soil moisture decrease in response to the massive re-vegetation occurred in a transition zone of grass-forest ecosystems with annual precipitation between 450 and 550 mm. Our study suggests that current AMSR-E JAXA retrievals are an essential alternative to field measurement and model simulation, because they can identify the location and spatial extent of areas where soil moisture is sensitive to climate change and managed re-vegetation. To avoid the overconsumption of soil water and limited plant growth in transition zone, managers of dryland areas should pay special attention to species selection.