Dominance of soil moisture over aridity in explaining vegetation greenness across global drylands

• Published in: The Science of the total environment Vol. 917; p. 170482
• Main Authors: Tripathi, Indra Mani, Mahto, Shanti Shwarup, Kushwaha, Anuj Prakash, Kumar, Rahul, Tiwari, Amar Deep, Sahu, Bidhan Kumar, Jain, Vikrant, Mohapatra, Pranab Kumar
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.03.2024
• Subjects: arid lands; Aridity; Australia; biodiversity; climate; Climate change; cropland; Cropland expansion; dry environmental conditions; Dryland area; ecosystems; Europe; humans; hydrometeorology; land use change; normalized difference vegetation index; Soil moisture; soil water; South Asia; vegetation; Vegetation greenness; water shortages; Australia; Europe; South Asia; Climate change; Cropland expansion; Soil moisture; Dryland area; Vegetation greenness; Aridity
• DOI: 10.1016/j.scitotenv.2024.170482
• ISSN: 0048-9697; 1879-1026

Drylands are one of the most sensitive areas to climate change. Despite being characterized by water scarcity and low precipitation, drylands support a wide range of green biodiversity and nearly 40 % of the global population. However, the climate change impacts on dryland characteristics and vegetation dynamics are debatable as the reasons remain poorly understood. Here, we use hydro-meteorological variables from ERA5 reanalysis and GIMMS-NDVI to analyze the changes in dryland aridity and vegetation greenness in the eight selected global dryland regions. The total dryland area (excluding hyperarid) has increased by 12 %, while arid, semiarid, and dry sub-humid areas have increased by 10.5 %, 8 %, and 25 %, respectively. We find a significant increase in aridity in drylands across the globe, except for South Asia. A decrease (increase) in precipitation is the major driver for a significant increase (decrease) in dryland aridity, with a notable contribution from climate warming. Despite decreasing trends in precipitation, vegetation greenness has significantly increased in most dryland regions due to increased soil moisture. Cropland expansion in Europe, Asia, and Australia resulted in the maximum increase in NDVI (Normalized Difference Vegetation Index) in dryland regions. The highest increase, with a ΔNDVI of 0.075, was observed in South Asia. The enhanced vegetation greenness observed is attributed to the expansion of croplands in recent decades, which has increased soil moisture. Overall, we show that monitoring soil moisture variability can provide a more robust explanation for vegetation greenness in the global drylands than aridity change. Moreover, human interventions of climatic alteration through land use change practices, such as cropland expansion, cannot be ignored while explaining the ecosystem dynamics of the drylands. [Display omitted] •A significant increase in aridity across global drylands was observed, except for South Asia.•The expansion of drylands in arid, semiarid, and dry sub-humid regions highlights escalating influence of climate change.•Vegetation greenness rises significantly despite decreased precipitation trends in most dryland regions.•The enhanced soil moisture in most of the drylands results from cropland expansion.