In Warmer Climate, Soil Drought and Atmospheric Aridity Will Lead to Rise in Drought

A world is heading towards a condition where it will experience more frequent and more extreme drought and aridity in the coming century than ever before. And, this will be exacerbated by both climate change and the dynamics that underlie land and atmosphere. A new study published in the journal PNAS reports these findings.

The study suggests that the concurrent soil drought and atmospheric aridity are driven by a series of land-atmosphere processes and feedback loops. In fact, these feedbacks would further intensify – more than ever – the concurrent drought and aridity in a warmer climate.

Soil drought is represented by very low soil moisture while atmospheric aridity is represented by very high vapour pressure deficit. The combination of high temperature and low humidity are the two factors that drive widerange vegetation mortality and reduced terrestrial carbon uptake. Earlier studies have focused on atmospheric and oceanic processes and their influence on driving climate changes.

“Concurrent soil drought and atmospheric aridity have dramatic impacts on natural vegetation, agriculture, industry, and public health. Future intensification of concurrent soil drought and atmospheric aridity would be disastrous for ecosystems and greatly impact all aspects of our lives’--," says Pierre Gentine, one of the authors of the study.

In their analysis, the researchers combined reanalysis datasets and model experiments to find out the land-atmosphere processes that have led to concurrent soil drought and atmospheric aridity. They then used climate models and statistical methods to predict how the land-atmosphere processes would further drive more frequent and intensified drought and atmospheric aridity in the future climatic conditions. The future climatic conditions are nothing but a warmer atmosphere. And as the climate warms, there would be further upsurge in atmospheric aridity. The land-atmospheric processes would further intensify the processes and lead to frequent droughts.

The main challenge that the research team was posed with was how to isolate the impact of land-atmosphere feedbacks on concurrent drought and aridity. After a large number of hit and trials, they found the CLACE-CMIP5 (Global Land Atmosphere Coupling Experiment – Coupled Model Intercomparison Project) as a convincing one.

Gentine’s group is the first to isolate this phenomenon and also is the first to obtain some dramatic findings.

“Most groups have been focused on assessing concurrent drought and heatwaves, but we are finding stronger coupling between drought and aridity than between drought and heatwaves. Concurrent drought and aridity also have a stronger impact on the carbon cycle and so we felt this was a critical point to study,” says Sha Zhou, the study's lead author.

The team found that the feedback that soil drought exert on atmosphere is largely responsible for the increase in the frequency and intensity of atmospheric aridity. Also, their findings revealed that the feedback of soil moisture and precipitation contributes to high frequency low precipitation and soil moisture conditions in many regions. These feedback processes in return would further increase the probability of concurrent soil drought and extreme aridity.

In the words of Gentine, “It's critical that we better quantify and evaluate the representation of these processes in our climate models. Accurate model representation of both soil moisture variability and the associated feedbacks is crucial if we are to provide reliable simulations of the frequency, duration, and intensity of compound drought and aridity events and of their changes in a warmer climate. Ultimately, this will help us mitigate future risks associated with these events."