Abstract
It is very important to analyze and monitor agricultural drought to obtain high temporal-spatial resolution soil moisture products. To overcome the deficiencies of passive microwave soil moisture products with low resolution, we construct a spatial fusion downscaling model (SFDM) using Moderate Resolution Imaging Spectroradiometer (MODIS) data. To eliminate the inconsistencies in soil depth and time among different microwave soil moisture products (Advanced Microwave Scanning Radiometer on the Earth Observing System (AMSR-E) and its successor (AMSR2) and the Soil Moisture Ocean Salinity (SMOS)), a time series reconstruction of the difference decomposition (TSRDD) method is developed to create long-term multisensor soil moisture datasets. Overall, the downscaled soil moisture (SM) products were consistent with the in situ measurements (R > 0.78) and exhibited a low root mean square error (RMSE < 0.10 m3/m3), which indicates good accuracy throughout the time series. The downscaled SM data at a 1-km spatial resolution were used to analyze the spatiotemporal patterns and monitor abnormal conditions in the soil water content across North East China (NEC) between 2002 and 2018. The results showed that droughts frequently appeared in western North East China and southwest of the Greater Khingan Range, while drought centers appeared in central North East China. Waterlogging commonly appeared in low-terrain areas, such as the Songnen Plain. Seasonal precipitation and temperature exhibited distinct interdecadal characteristics that were closely related to the occurrence of extreme climatic events. Abnormal SM levels were often accompanied by large meteorological and natural disasters (e.g., the droughts of 2008, 2015, and 2018 and the flooding events of 2003 and 2013). The spatial distribution of drought in this region during the growing season shows that the drought-affected area is larger in the west than in the east and that the semiarid boundary extends eastward and southward.
Highlights
Soil moisture (SM) is the primary indicator of climate change and has been defined as an essential climate variable by the Global Climate Observing Systems [1]
The results showed that droughts frequently appeared in western North East China and southwest of the Greater Khingan Range, while drought centers appeared in central North East China
The soil types in North East China are dominated by high-fertility black soil
Summary
Soil moisture (SM) is the primary indicator of climate change and has been defined as an essential climate variable by the Global Climate Observing Systems [1]. Temporal and spatial information on SM can be obtained through multiple approaches, such as in situ measurements and remote sensing (RS) methods. Measuring SM at a single location does not necessarily represent the conditions of the entire region, only RS can provide real-time dynamic observations at regional to global scales [6,7]. Over the past several decades, RS has become a practical method for deriving SM information, especially in remote countryside areas with limited ground measurements [8]. Several approaches for retrieving SM based on RS data exist, such as those based on visible/infrared (IR) and microwave observations [9]
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