Drought-induced vulnerability and resilience of different land use types using time series of MODIS-based indices

Drought is a creeping and complex phenomenon that significantly impacts terrestrial ecosystem services by reducing the ecosystem's performance and upsetting the balance of the terrestrial carbon cycle. This study used Google Earth Engine (GEE) to quantify the effects of drought on the vulnerability and resilience of land use and land cover (LULC) types in the Karkheh basin, Iran's food basket and the third-largest basin in southwest Iran. Using MODIS data, we first extracted the vegetation health index (VHI) for drought monitoring during 2000–2020, and as a result, 2008 was designated as the drought year. Then, water use efficiency (WUE) was calculated for all LULC types during drought. In general, all LULC types experienced an increase in WUE, with the highest increase seen in the forest, which indicates the forest's high resistance to drought. To evaluate the ecosystems' resilience to drought, we computed the drought recovery period using the gross primary production (GPP). The results showed that recovery times varied among different LULC types, with the forest recovering in the shortest time, further indicating a higher resilience and greater importance for the absorption and stabilization of terrestrial carbon. Conversely, rainfed farming had the longest recovery time, indicating a higher vulnerability and, consequently, a greater need for the adoption of appropriate adaptive measures. The results of this study provide a better understanding of the response of different LULC types and their resilience to drought and can assist ecosystem conservation and LULC management.