Cracked soil. PHOTO/USGS
Key Points
- An increasingly moisture-limited world under global warming depends on more than just reduced soil moisture
- Earth system models inconsistently simulate the critical soil moisture value that separates moisture-limited and energy-limited regimes
- Poor agreement among models on projected changes in critical soil moisture calls for greater focus on its observation and validation
By PATRICK MAYOYO
A new study shows that climate change is drying out the Earth’s soils exacerbating extreme weather events, including droughts and heat waves among other impacts of climate change.
The study, Hsu et al. quantify how global warming affects soil moisture adding although climate change will dehydrate soil, they found, it is not clear how dry is too dry.
The team examined several Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models and found that if carbon dioxide increased by 1% every year, after about 125 years, soils would dry and the world would become much more moisture limited.
Still, the models disagreed on the threshold at which Earth would become a more moisture-limited system—a value called critical soil moisture. That threshold depends on myriad factors both on land and in the atmosphere.
The scientists behind the study say critical soil moisture has wide-ranging impacts on the water cycle, climate, ecosystems, and society. Getting a solid grasp on that value would improve climate models and paint a fuller picture of Earth’s Future.
The study published by AGU-Advancing Earth and Space Science, shows evaporation is controlled by soil moisture (SM) availability when conditions are not extremely wet and in such a moisture-limited regime, land-atmosphere coupling is active, and a chain of linked processes allow land surface anomalies to affect weather and climate.
“How frequently any location is in a moisture-limited regime largely determines the intensity of land feedbacks on climate. Conventionally this has been quantified by shifting probability distributions of SM, but the boundary between moisture-limited and energy-limited regimes, called the critical soil moisture (CSM) value, can also change,” the study notes.
CSM is an emergent property of the land-atmosphere system, determined by the balance of radiative, thermal and kinetic energy factors. We propose a novel framework to separate the contributions of these separate effects on the likelihood that SM lies in the moisture-limited regime.
“We confirm that global warming leads to a more moisture-limited world. This is attributed to reduced SM in most regions: the moisture effect. CSM changes mainly due to shifts in the surface energy budget, significantly affecting 27.7% of the globe in analyzed climate change simulations,” the scientists say
The experts however, observe consistency among Earth system models regarding CSM change is low and the poor agreement hints that variability of CSM in models and the factors that determine CSM are not well represented.
“The fidelity of CSM in Earth system models has been overlooked as a factor in water cycle projections. Careful assessment of CSM in nature and for model development should be a priority, with potential benefits for multiple research fields including meteorology, hydrology, and ecology,” they add.
