Abstract
Soil moisture reanalysis products can provide soil water information for the surface and root zone soil layers, which are significant for understanding the water cycle and climate change. However, the accuracy of multi-layer soil moisture datasets obtained from reanalysis products remains unclear in some areas. In this study, we evaluated the root zone soil moisture of the ERA-Interim soil moisture product, as well as the surface soil moisture based on in situ measurements from the OzNet hydrological measurement network over southeast Australia. In general, the ERA-Interim soil moisture product presents good agreement with in situ soil moisture values and can nicely reflect time variations, with correlation coefficient (R) values in the range of 0.73 to 0.84 and unbiased root mean square difference (ubRMSD) values from 0.035 m3·m−3 to 0.060 m3·m−3. Although the ERA-Interim soil moisture also can reflect temporal dynamics of soil moisture at root zone layer at depths of 28–100 cm, low correlations were found in winter. In addition, the ERA-Interim soil moisture product overestimates in situ measurements at depths of 0–7 cm and 7–28 cm, whereas the product shows underestimated values compared with in situ soil moisture at the root zone of 28–100 cm. Consequently, the ERA-Interim soil moisture product has both high absolute and temporal accuracy at depths of 7–28 cm, and the ERA-Interim soil moisture product can nicely capture temporal dynamics at all the evaluated soil level depths, except for the depth of 28–100 cm during the winter months. The contributions of terrain, vegetation cover, and soil texture to the model error were addressed by feature importance estimations using the random forest (RF) algorithm. Results indicate that terrain features may have an impact on the model errors. It is clear that the accuracy of the ERA-Interim soil moisture can be improved by adjusting the assimilation scheme, and the results of this study are expected to provide a comprehensive understanding of the model errors and references for optimizing the model.
Highlights
Soil acts as an important container for water on Earth [1]
The results showed the ERA-Interim reanalysis soil moisture product captured the variation of in situ surface soil moisture well and provided close absolute values of the soil moisture observations of surface soil [26,31,32]
Root zone soil moisture is as important as surface soil moisture in various hydrological models
Summary
Soil acts as an important container for water on Earth [1]. Soil water plays a significant role in the water cycle, and is a key medium between precipitation, vegetation water, and underground water [2].Water 2018, 10, 1123; doi:10.3390/w10091123 www.mdpi.com/journal/waterThe measurement of soil water content is helpful for our understanding of the global water cycle, as well as the occurrence and development of flooding and drought disasters [3,4,5]. Soil acts as an important container for water on Earth [1]. Soil water plays a significant role in the water cycle, and is a key medium between precipitation, vegetation water, and underground water [2]. The measurement of soil water content is helpful for our understanding of the global water cycle, as well as the occurrence and development of flooding and drought disasters [3,4,5]. The soil water is a key variable in various hydrological and surface runoff models. Soil moisture datasets are urgently needed in multiple hydrological applications and climatic studies [6]. Satellite remote sensing has provided innovation in observational approaches of soil moisture, making global observations of soil moisture possible at high temporal resolutions [7,8,9,10,11,12]
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