Recent Global Distribution of Aridity Index and Land Use in Arid Regions

Drylands, which occupy 41% of Earth's land area, have large effects on Earth's climate via land-atmosphere interactions, and simulations of future climate indicate that drylands will be very sensitive to climate changes associated with global warming. Monitoring of drylands is therefore necessary to help guide sustainable development in drylands and to protect the global environment. This study examined changes of the global distribution of the aridity index from 2000 to 2020 and compared them to changes from 1951 to 1980. The regions with relatively wet climates, that is, semi-arid and dry sub-humid regions, became drier from 2000 to 2020. The largest use of land in drylands was grassland, followed by open shrubland, cropland, savanna, and woody savanna. More than 50% of dry land was accounted for by grasslands (18,651,109 km²) and dryland forests including shrubland and savanna (13,331,231 km²). The relationship between the aridity index and the normalized difference vegetation index indicated that the value of the aridity index of dryland forests and grasslands equaled the threshold for climatically stable existence, although the range of the aridity index was wide in both cases. We also made rough assessments of soil organic carbon sequestration in dryland forests and grasslands.