麻豆淫院

Soil moisture is a key regulator of temperature and humidity, one that's positioned to be affected substantially by climate change. But despite the importance of soil moisture, efforts to model it involve dozens of poorly constrained parameters, and different models tend to disagree about how soil moisture levels will change in a warming world.

Tara Gallagher and Kaighin A. McColl took a "radically simpler" approach and modeled soil moisture solely in terms of precipitation and net surface radiation. Their study is in Geophysical Research Letters.

The model worked well when tested using both fifth-generation European Center for Medium-Range Weather Forecasts atmospheric reanalysis (ERA5) and Coupled Model Intercomparison Project Phase 6 (CMIP6) climate datasets.

That's surprising, the researchers say, because the simple model excludes measurements that much of the recent literature has focused on: vapor pressure deficit (the difference between the amount of moisture the air has the capacity to hold and the amount it is actually holding) and atmospheric carbon dioxide (CO₂) levels. Both are expected to rise alongside greenhouse gas emissions.

The researchers suggest their model still works well because vapor pressure deficit is a poor measure of atmospheric demand for water; net surface radiation, which is included in the model, is a better measure. In regard to CO₂, the researchers say that some prior studies have overestimated the role of the gas.

The simple model offers potential answers to two fundamental questions about soil moisture: (1) Why does soil moisture follow a W-shaped longitudinal profile, with high moisture at the equator and poles and low moisture in between, and (2) why does soil moisture increase with warmer temperatures in some locations but decrease in others?

The W-shaped profile may be caused by a combination of precipitation rates and radiation intensity. High precipitation near the equator dominates the model and causes high soil moisture. The midlatitudes and the poles both see moderate levels of precipitation. But the midlatitudes receive more intense radiation than the poles, which leads to comparatively drier midlatitude soils.

As for the second question, the researchers suggest warming may have varying effects on soil moisture because warming can come with both increased precipitation, which raises soil moisture, and increased net surface radiation, which lowers soil moisture. These two variables balance each other out to different degrees at different locations, meaning that warming sometimes raises soil moisture and sometimes lowers it.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story .