Abstract
Soil moisture is a key variable in the process of land–atmosphere energy and water exchange. Currently, there are a large number of operational satellite-derived soil moisture products and reanalysis soil moisture products available. However, due to the lack of in situ soil moisture measurements over the Tibetan Plateau (TP), their accuracy and applicability are unclear. Based on the in situ measurements of the soil moisture observing networks established at Maqu, Naqu, Ali, and Shiquanhe (Sq) by the Institute of Tibetan Plateau Research, the Chinese Academy of Sciences, the Northwest Institute of Eco-Environmental Resources, the Chinese Academy of Sciences and the University of Twente over the TP, the accuracy and reliability of the European Space Agency Climate Change Initiative Soil Moisture version 4.4 (ESA CCI SM v4.4) soil moisture products and the European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) soil moisture product were evaluated. The spatiotemporal distributions and interannual variations of the soil moisture were analyzed. Further, the climatological soil moisture changing trends across the TP were explored. The results show that with regard to the whole plateau, the combined product performs the best (unbiased root-mean-square error (ubRMSE) = 0.043 m3/m3, R = 0.66), followed by the active product (ubRMSE = 0.048 m3/m3, R = 0.62), the passive product (ubRMSE = 0.06 m3/m3, R = 0.61), and the ERA5 soil moisture product (ubRMSE = 0.067 m3/m3, R = 0.52). Considering the good spatiotemporal data continuity of the ERA5 soil moisture product, the ERA5 soil moisture data from 1979 to 2018 were used to analyze the climatological soil moisture changing trend for the entire TP surface. It was found that there was an increasing trend of soil moisture across the TP, which was consistent with the overall trends of increasing precipitation and decreasing evaporation. Moreover, the shrinkage of the cryosphere in conjunction with the background TP warming presumably contribute to soil moisture change.
Highlights
The Tibetan Plateau (TP), known as the ‘Third Pole of the Earth’, is the highest and most extensive plateau in the world, with a mean elevation of more than 4000 m above sea level
The main objective of this study is to determine the accuracy of the latest European Space Agency (ESA) CCI SM v4.4 soil moisture products and the European Centre for Medium-Range Weather Forecast (ECMWF) Reanalysis 5 (ERA5) soil moisture product over the TP and to further identify the soil moisture changing trends and their relationship with precipitation and evaporation over the TP under the background of climate change
the Microwave Imager (TMI), where n is the total number of years, xi is the value of the soil moisture in the ith year, and x = ∑ x, i = 1,2,3, ... , n; t = ∑ i
Summary
The Tibetan Plateau (TP), known as the ‘Third Pole of the Earth’, is the highest and most extensive plateau in the world, with a mean elevation of more than 4000 m above sea level. The thermal and dynamic effects of the TP have an extremely drastic impact on Asian monsoon patterns, global atmospheric circulation, and climate change [1]. An accurate soil moisture observation dataset is expected to provide crucial information and initial input data for climate change analysis and numerical simulation over the TP [2,3]. Due to the extreme geographical environment and harsh climatic conditions, in situ measurements are restricted to a very small spatial scale and only cover a limited temporal range. There has been a lack of soil moisture measurements in the ’Third Pole’ region for a long time, which is insufficient to meet the needs of plateau climate change research
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