Abstract
The European Space Agency Climate Change Initiative Soil Moisture (ESA CCI SM) product provides soil moisture estimates from radar satellite data with a daily temporal resolution. Despite validation exercises with ground data that have been performed since the product’s launch, SM has not yet been consistently related to soil water storage, which is a key step for its application for prediction purposes. This study aimed to analyse the relationship between soil water storage (S), which was obtained from soil water balance computations with ground meteorological data, and soil moisture, which was obtained from radar data, as affected by soil water storage capacity (Smax). As a case study, a 14-year monthly series of soil water storage, produced via soil water balance computations using ground meteorological data from northeast Portugal and Smax from 25 mm to 150 mm, were matched with the corresponding monthly averaged SM product. Linear (I) and logistic (II) regression models relating S with SM were compared. Model performance (r2 in the 0.8–0.9 range) varied non-monotonically with Smax, with it being the highest at an Smax of 50 mm. The logistic model (II) performed better than the linear model (I) in the lower range of Smax. Improvements in model performance obtained with segregation of the data series in two subsets, representing soil water recharge and depletion phases throughout the year, outlined the hysteresis in the relationship between S and SM.
Highlights
Hydrological processes occurring on the Earth’s surface and interacting with the lower atmosphere are key to understanding atmospheric dynamics and climate change and their effects on the global water cycle
Portugal that was aimed at analysing the statistical relationship between soil water storage, which was obtained from soil water balance computations with ground meteorological data, and soil moisture, as given by the European Space Agency (ESA) Climate Change Initiative (CCI) SM product
Dorigo et al [43] compared the ESA CCI SM combined product with in-situ-based soil moisture observations recorded by the validation ground stations network
Summary
Hydrological processes occurring on the Earth’s surface and interacting with the lower atmosphere are key to understanding atmospheric dynamics and climate change and their effects on the global water cycle In this context, soil moisture is one of the essential climate variables (ECVs) [1,2] playing an important role in the climate dynamics [3] and change [4,5], the water cycle and the soil–atmosphere energy exchange [6]. The soil water balance is a valuable tool for analysing the impacts of land-use changes on soil water storage and to designing adaptation strategies for global change scenarios as far as water resources management is concerned
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