Spatiotemporal Patterns of Vegetation Stress and Hydroclimatic Responses in the CWANA Region (2000–2024)

Abstract

Understanding the characteristics of vegetation stress and their responses to hydroclimatic variability is critical for assessing ecosystem resilience and predicting ecological trajectories under ongoing global climate change. The CWANA region is among the most significant vegetation ecosystems, with a massive expanse of drylands. This study provides a detailed analysis of the spatiotemporal characteristics of vegetation stress and its influencing factors (precipitation, temperature, and soil moisture) in the region, using monthly MODIS-based vegetation condition index time series from 2000 to 2024. The findings of this study revealed that nearly 59% of the vegetated areas experienced 10–20 stress events, particularly observed in Kazakhstan and Ethiopia. The most prolonged stress events lasted nearly 17 months and were recorded in parts of Pakistan and the Horn of Africa. Almost 43% of major stress events occurred in the early 2000s, whereas recent years have witnessed non-stressed conditions. Despite several major stress occurrences, the vegetation in the study region exhibited an overall positive trend over the study period. Turkey and Pakistan experienced among the strongest greening trends. A stronger positive trend in vegetation was primarily observed in forests (mixed and evergreen) and cropland (an increase of around 1.5% per year). In contrast, grassland and shrubland exhibited a lower trend. Among the influencing factors, soil moisture accounts for the largest share of significant partial correlation coefficients (32.4% of the study area), followed by temperature. When stratified by land-cover, elevation, and aridity classes, the influence of soil moisture is strongest at lower elevations, in arid and semi-arid environments, and across rainfed croplands and mixed forest systems, where it accounts for roughly 35–36% of the total influence. This study provides critical insights into the spatiotemporal patterns of vegetation stress in relation to climate and soil moisture under ongoing global climate change and the expansion of drylands.