Temporal changes and dynamics of dryland ecosystem variables and their relation to aridity

Prolonged droughts, heat waves and increasing aridity in general are considered consequences of global climate change. Such phenomena are likely to alter the structural and functional attributes as well as the dynamics of ecosystems in general and drylands in particular. Being naturally limited in water and natural resources; and mainly located in developing countries, drylands are especially vulnerable to potential adverse consequences of climate change. Moreover, arid, dryland-like conditions and mechanisms are expected to gain importance in rather humid climatic zones as well. Yet, detailed knowledge about temporal dynamics and responses of drylands, particularly their components, structure and functioning, such as vegetation cover, productivity and composition as well as soil properties to increasing aridity are largely unknown. Here, we investigate how several structural and functional ecosystem variables respond to aridity [calculated as 1 (precipitation/potential evapotranspiration)] in global drylands from 2000 to 2020. Moreover, based on the framework of abrupt ecosystem changes characterized by consecutive aridity thresholds (Berdugo et al., 2020), we identified focus areas that had crossed one or several aridity thresholds in the past 20 years (areas likely to have undergone severe, potentially non-reversible structural/ functional changes) to study ecosystem variables within. In particular, the temporal dynamics of remotely sensed metrics relating to vegetation cover, productivity, functioning, composition, biomass, climate and soil quality were analyzed. We characterize linear and abrupt changes within these variables, their relation to aridity and present an overview of hot spot areas of change.