Soil moisture-evaporation coupling shifts into new gears under increasing CO2

Abstract

When soil moisture content (SM) falls within a transitional regime between dry and wet, it controls evaporation rates, affecting atmospheric heat and humidity. Accordingly, different SM regimes correspond to different gears of land-atmosphere coupling, affecting climate. Determining patterns of SM regimes and their future changes is imperative. Global distributions of shifts between SM regimes from eight climate models are examined. Under increasing CO2, the range of SM extends into unprecedented coupling regimes in many locations. SM in many arid regions migrates from the transitional toward the dry regime, while an opposite migration appears in semiarid regions. Transitional regimes also emerge in currently humid areas of the tropics and high latitudes. These changes imply that a larger fraction of the world will evolve to experience more than one gear of land-atmosphere coupling, with the strongly coupled transitional regime growing the most. Furthermore, the locally predominant gear may change under global warming.

Uncertainty in Projected Critical Soil Moisture Values in CMIP6 Affects the Interpretation of a More Moisture‐Limited World

“…This is of benefit to investigations of climate extremes, hydrology, and phenology, in which variations in land‐atmosphere interactions play a crucial role. Results presented here and from past studies (Dirmeyer et al., 2013; Hsu & Dirmeyer, 2023; Jung et al., 2010; Zhou et al., 2021) indicating a more‐moisture limited world under global warming is brought into question by the large spread of CSM responses among CMIP6 models. Based on this uncertainty in modeled CSM, future studies should put more effort toward examination and validation of CSM.…”

“…Using such approaches, SM regimes have been diagnosed for the current era and examined under projected climate change (Hsu & Dirmeyer, 2023; Denissen et al., 2022). The quantification of CSM and its variations is rarely discussed in the Earth science context, even though it is as informative and impactful as SM or precipitation for understanding the water cycle over land.…”

Shift of soil moisture-temperature coupling exacerbated 2022 compound hot-dry event in eastern China

“…There is an increase in the sensitivity of air temperature to drying soil when soil moisture becomes extremely low, leading to positive soil moisture-temperature feedback that intensifies heatwaves and droughts (Benson and Dirmeyer 2021). Such positive feedback typically occurs in semiarid and arid regions, where latent heat flux is largely limited by soil water availability (Seneviratne et al 2010, Hsu andDirmeyer 2023). The YZB is a typical energylimited region (Dong et al 2023) with annual mean precipitation exceeding 800 mm (Gao et al 2020).…”

Even cooler insights: On the power of forests to (water the Earth and) cool the planet

“…Such phenomena upset the delicate, natural, preanthropogenic surface energy equilibrium described above and established over millennia. Increasing heat wave invasions radiate out from the inner latitudes toward the poles, posing the greatest threats to the cooling power of forests, not to mention tree and forest survival, from the inner latitudes on out (and not from the outer latitudes on in) (see, e.g., Hsu & Dirmeyer, 2023; Li et al., 2022).…”