Drought Assessment in Tunisia by Time-Series Satellite Images: An Ecohydrologic Approach

Abstract

Global and regional monitoring of drought are becoming an active research subject during the last decades. In the Middle East and North Africa (MENA) region drought episodes highly control water availability and the functioning of both forested and cultivated ecosystems. The ecohydrologic approach represents a relatively new trend in the holistic assessment of these limited water resources ecosystems as it explains the equilibrium between the components of the soil-vegetation-climate complex. On the other hand, during the last two decades, the models used in the assessment of drought causes and manifestations combine more and more indicators from multi-sensors satellite images. In the present study, the ecohydrology concepts and their methodological basis are presented, and an overview of biophysical and energetic variables derived from remote sensing data at the regional scale are exposed. A general review of the use of remote sensing in ecohydrology during the last two decades is also addressed as well as various methods using satellite images in the ecohydrologic modelling. These methods are divided into two major groups: the direct use of remote sensing in drought and humidity assessment, and the integration of satellite images with other data in water balance models for hydric stress assessment. The ecohydrological modelling integrating remote sensing data makes use of different types of models such as statistical, empirical or physical based models. The availability of free time series satellite images such as MODIS sensors since the year 2000 had allowed the exploration of various models for drought assessment where multispectral images are combined to derive drought indicators of the vegetation in a Tunisian Mediterranean ecosystem. Finally, data quality of time-series images and their calibration and correction are discussed to highlight the required processing for convenient use of these data in drought monitoring at the regional scale.