Assessment of Drought Characteristics, and Its Impacts on Vegetation and Wheat Yield in Tunisia

Tunisia, located on the shores of the Mediterranean, is projected to experience most predominant droughts. However, detailed drought assessments at the regional scale of Tunisia are limited to date, with most studies only focusing on a specific region and/or making use of one drought index. This study identifies both vegetation and agricultural region-specific drought indices over the country. Tunisia was divided into three main vegetation zones: the northern forest, central steppe, and southern desert. Monthly meteorological (Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI)) and soil moisture (Palmer Drought Severity Index (PDSI) and soil moisture percentiles, W_p) drought indices were used to analyze drought characteristics using gridded-meteorological and ground-measured soil data, and compared with the weekly Normalized Difference Vegetation Index (NDVI) and the winter wheat yield data to assess vegetation and agriculture responses to drought, respectively. We found that short-term meteorological droughts were frequent, triggering soil moisture droughts that were more persistent and severe. The most important finding of this study was that SPI is the best indicator for assessing a drought impact on both vegetation and agriculture in the northern forest, while PDSI in the central steppe for vegetation and agriculture and in the southern desert for vegetation (no agricultural data on southern desert). The results of this study highlight the importance of region-specific drought indices which are most likely to provide a very useful measure for drought monitoring and mitigation in Tunisia.