Desert dust suppressing precipitation: A possible desertification feedback loop

TLDR

Desert dust has been theorized to enhance rainfall, but anthropogenic land‑use changes that expose topsoil can trigger a desertification feedback loop. Satellite and aircraft observations show that dust‑laden clouds contain small droplets that coalesce poorly, and chemical analysis of Saharan dust particles indicates a mechanism for reduced rainfall. Observations reveal that desert dust suppresses precipitation—a smaller but significant effect than smoke—and the resulting drier soils can amplify dust emissions, creating a feedback loop that further reduces rainfall.

Abstract

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.