SMOS-derived soil moisture anomalies and drought indices: A comparative analysis using in situ measurements

Abstract

The objective of this analysis is to demonstrate the feasibility of using a composite L2 Soil Moisture and Ocean Salinity (SMOS) soil moisture product for determining drought conditions by taking advantage of its spatial and temporal resolutions. The work investigates the potential relationships between soil moisture anomalies and two drought indices, the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index, both calculated on a ten-day basis. As the two drought indices can be applied to different time scales for precipitation series, the influence of time scale on the drought definition is also studied. The anomalies were calculated both for the in situ soil moisture by REMEDHUS (Soil Moisture Measurement Stations Network, Spain) and from the SMOS L2 soil moisture product. In general, in situ anomalies exhibit higher correlation coefficients for the drought indices than those of SMOS, except for the shortest time scale. As expected, the short-term remotely sensed anomalies have a high response to precipitation events. This effect may be due to the greater sensitivity of SMOS data to rainfall, as well as to the spatial averaged nature of its observations. The optimal time scale was 1month for the SMOS values and ranged between 30 and 50days for the in situ values. The use of evapotranspiration in the calculation of the indices did not improve the description of the anomalies. The relationship between indices and soil moisture conditions provides encouraging results. Indeed, this method generates preliminary but valuable insights for future satellite products. © 2014 John Wiley & Sons, Ltd.