Assessment of Vegetation Changes in Saudi Arabia Using Harmonic Analysis and ENSO Indices

Arid environment with limited vegetation and scare water resources characterizes Saudi Arabia (SA). Therefore, studying the changes and trends of vegetation conditions is of high importance, especially considering the impact that climate change is likely to have on the living standards and food security in the near future. In this research, the enhanced vegetation index (EVI) is applied as an indicator of the drying trends over the SA region in the past 20 years. The soil moisture products, vegetation, and precipitation-based products are assessed to monitor and predict the variability of vegetation distribution. Overall, the vegetation in SA has a declining trend in most of its habitats, with the exception of regions with cropland reclamation. Most of the wild sparse vegetation areas (such as grassland and shrubland) suffer decreasing trends in the southwestern mountains. The findings suggest that soil moisture and EVI of five major vegetation categories react differently to the precipitation. Interestingly, a comparably positive relationship between the SA’s NDVI and Trans-Niño Index (TNI) is shown over the other El Niño indices, with increasing lag correlation from 0 to 11 months. This may indicate the teleconnection between El Niño events, eastern Pacific El Niño in particular, and vegetation richness in SA.