Interactions between precipitation, evapotranspiration and soil-moisture-based indices to characterize drought with high-resolution remote sensing and land-surface model data

Abstract

Abstract. The Iberian Peninsula is prone to drought due to the high variability in the Mediterranean climate with severe consequences for drinking water supply, agriculture, hydropower and ecosystem functioning. Because of the complexity and relevance of droughts in this region, it is necessary to increase our understanding of the temporal interactions of precipitation, evapotranspiration and soil moisture that originate from drought within the Ebro basin, in northeastern Spain, as the study region. Remote sensing and land-surface models provide high-spatial-resolution and high-temporal-resolution data to characterize evapotranspiration and soil moisture anomalies in detail. The increasing availability of these datasets has the potential to overcome the lack of in situ observations of evapotranspiration and soil moisture. In this study, remote sensing data of evapotranspiration from MOD16A2 and soil moisture data from SMOS1km as well as SURFEX-ISBA land-surface model data are used to calculate the evapotranspiration deficit index (ETDI) and the soil moisture deficit index (SMDI) for the period 2010–2017. The study compares the remote sensing time series of the ETDI and SMDI with the ones estimated using the land-surface model SURFEX-ISBA, including the standardized precipitation index (SPI) computed at a weekly scale. The study focuses on the analysis of the time lags between the indices to identify the synchronicity and memory of the anomalies between precipitation, evapotranspiration and soil moisture. Lag analysis results demonstrate the capabilities of the SPI, ETDI and SMDI drought indices computed at a weekly scale to give information about the mechanisms of drought propagation at distinct levels of the land–atmosphere system. Relevant feedback for both antecedent and subsequent conditions is identified, with a preeminent role of evapotranspiration in the link between rainfall and soil moisture. Both remote sensing and the land-surface model show capability to characterize drought events, with specific advantages and drawbacks of the remote sensing and land-surface model datasets. Results underline the value of analyzing drought with dedicated indices, preferably at a weekly scale, to better identify the quick self-intensifying and mitigating mechanisms governing drought, which are relevant for drought monitoring in semi-arid areas.

Toward a Redefinition of Agricultural Drought Periods—A Case Study in a Mediterranean Semi-Arid Region

“…The result is an asymmetrical interaction between the VCI and the SPI. This outcome is coherent with the findings of [30] comparing the evapotranspiration deficit index with the SPI. Those authors interpret this loss of asymmetry as the increase in aggregation.…”

“…Therefore, interactions between land-soil atmosphere variables are fast-moving in a semi-arid Mediterranean climate. Hence, some studies recommend short time scales for drought assessment [30]. Multi-monthly aggregation has already been tackled with the multi-scalar approach of the SPI; nevertheless, smaller aggregations are generally not considered, because the SPI becomes very noisy.…”

“…There is an evident propagation of drought through the different compartments of the atmosphere to the groundwater continuum [17]. However, cross-correlations studies have also shown that propagation is complex to identify through indices or remote sensing observations [30], especially for agricultural drought. The logical precedence of one index to the other is not always observed, which may be due to the use of different input data (models and satellite observations) and different spatial scales [29].…”

A Copernicus-based evapotranspiration dataset at 100-m spatial resolution over the Mediterranean region

“…Precipitation patterns also vary across the region. The south-eastern part experiences low precipitation (350-700 mm yr −1 ), while the mountain regions receive more rainfall yielding 800-2000 mm per year (Gaona et al, 2022). To meet the water demands of the entire EB, extensive canal systems have been developed, and around 92% of the total water consumption is allocated to irrigation and farming (Barella-Ortiz et al, 2023).…”

Drought Propagation under Combined Influences of Reservoir Regulation and Irrigation over a Mediterranean Catchment

“…Land surface models (LSMs) have been widely recognized as a powerful tool for understanding and simulating the hydrological cycle, including droughts [10][11][12][13]. Particularly in Spain, LSMs have been used to evaluate and provide information on water availability and potential drought hotspots [14,15]. Nevertheless, for more realistic modeling of droughts, it is crucial to incorporate the representation of human factors in currentgeneration LSMs [16].…”