Temperatures are rising, but soil is getting wetter, confounding climate theorists

One overlooked factor was the CO2 fertilization effect in plant photosynthesis. The researchers found that “it’s virtually impossible to predict soil moisture in the coming decades”, contrary to some alarmist notions about future droughts.
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Soil moisture can determine how quickly a wildfire spreads, how fast a hill turns into a mudslide and, perhaps most importantly, how productive our food systems are, says Eurekalert.

As temperatures rise due to human-caused climate change [Talkshop comment – evidence-free assertion of cause], some researchers are concerned that soils will dry.

However, between 2011 to 2020, soil moisture increased across 57% of the United States during summer, the warmest time of year.

Why did soil get wetter even as the planet got hotter?

A recent paper from Harvard University researchers found that precipitation, rather than temperature, overwhelmingly explains soil moisture trends.

While it’s not surprising that more rain means wetter soil, the research challenges a long-standing assumption that increases in global temperatures will lead to drier soils.

“Atmospheric water has often been used as a proxy for drought, but this paper highlights distinctions between the hydroclimate of soils and the temperature and hydroclimate of the atmosphere,” said Peter Huybers, Professor of Earth and Planetary Sciences in the Faculty of Arts and Sciences and of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences, and senior author of the paper.

The research team found that drying from increased temperature was largely balanced by CO2 fertilization, which allows plants to use water more efficiently.

Both these effects are secondary relative to rainfall and tend to cancel each other out — leaving precipitation as the primary driver of soil moisture.

One challenge in studying soil moisture is a sparsity of data and the frequent disconnect between satellite data and ground level observations. The team compared ground level observations between 2011 and 2020 — the short time period during which many soil moisture measurements are available across the United States — with satellite data and found a similar increase in soil moisture.

These findings highlight the importance of improving predictions of long-term changes in precipitation in response to climate change, especially in relation to food production.
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“Our results suggest that reduced surface soil moisture is far from a foregone conclusion given the uncertainty in precipitation trends around the globe,” said Huybers. “With uncertainties in the interannual variability of rainfall and uncertainties in predictions of long-term rainfall, it’s virtually impossible to predict soil moisture in the coming decades.”

Full article here.
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Image: Photosynthesis [Credit: Nefronus @ Wikipedia]