Recent changes in global drylands: Evidences from two major aridity databases

Drying of terrestrial areas is a critical issue in our era of climate change. However, there is limited knowledge on the current spatial status of drylands, which can be assessed using updated and more rigorous data than information used in the initial dryland estimations. Here we investigate the current extent of drylands globally, continentally and nationally by analysing one of the most recent aridity database (1950-2000 period) and compare statistically, for the first time, with the initial dryland estimations (1951-1980). Using diachronic analysis between the databases, we found that drylands are currently almost 4% larger worldwide than expected and cover 45.4% of the Earth's land surface. This net increase of global dryland areas is due to the expansion of arid (+3.4%) and semi-arid (+0.9%) areas, whilst hyper-arid zones decreased (-0.8%) and dry sub-humid areas remained stable. Except for Europe and South America, all continents have experienced a net expansion of arid environments in the recent climate database. Our findings show that Asia is home to the world's largest increases in dryland areas, where China alone accounts for almost one third of the new lands exposed to aridity worldwide. The Earth's drier conditions can generally be attributed to climate changes occurring after 1980. Our results highlight large-scale drying processes and therefore the exacerbation of land degradative conditions at low and middle latitudes. Also, our findings signal the danger of triggering certain positive feedbacks in global warming, considering the newly-identified drylands migration towards higher latitudes in North America and Asia, which can modify the albedo and destabilize the large carbon pools in permafrost, peatlands or boreal forests.