Friday, January 28

The drylands are not drying up anymore

A study underscores the need to improve predictions of soil moisture.

A study underscores the need to improve predictions of soil moisture.

The Humidity of floor in arid lands exerts a negativfeedbackk on the availability of surface water, offsetting part of the expected decrease.

It is the conclusion of a new study from the School of Engineering and Applied Sciences at Columbia University (Columbia Engineering), the first to investigate the long-term effect of feedback from soil and atmospheric moisture in dry lands.

Scientists have thought that global warming increase the availability of surface water (freshwater resources generated by precipitation minus evapotranspiration) in humid regions and water availability will decrease in dry regions.

This expectation is based primarily on atmospheric thermodynamic processesOf As the air temperature increases, more water evaporates from the ocean and landOf Because warmer air can hold more water vapor than dry air, a more humid atmosphere is expected to amplify the existing pattern of water availability, causing atmospheric responses of “dry-dries-wetter-gets-wet-more” global warming.

A Columbia engineering team led by Pierre Genuine, professor of earth and environmental engineering and affiliate Earth Institute, wondered why coupled climate model predictions do not project significant “drier” responses over dry lands, tropical and temperate areas with an aridity index of less than 0.65, even when researchers use the scenario emissions from global warming.

Sha Zhou, postdoctoral fellow at the Lamont-Doherty Earth Observatory and the Earth Institute studying land-atmosphere interactions and the global water cycle, thought that the feedback from soil and atmosphere moisture could play an important role in future predictions of water availability in dry lands.

The new study, published this Monday in the journal ‘Nature Climate Change’, is the first to show the importance of long-term changes in soil moisture and associated reactions between soil moisture and the atmosphere in these predictions.

The researchers identified a long-term regulation of soil moisture from atmospheric circulation and moisture transport that greatly enhances the potential decline in future water availability in dry lands, beyond what is expected in the absence of feedback from soil moisture.

Thesfeedbackk play a bigger role than you think on long-term surface water changes, ” Zhouou saysOf Since variations in soil moisture negatively affect water availability, this negativfeedbackk could also partially reduce warming-induced increases in the magnitudes and frequencies of extremely high and extremely lohydro climaticic events, such as droughts and floodsOfWithout negativfeedbackk we could experience more frequent and extreme droughts and floods“, he warns.

The team combined a unique and idealized multi-model earth-atmosphere coupling experiment with a novel statistical approach they developed for the studyOf They then applied the algorithm in observations to examine the critical role of feedback from soil and atmospheric moisture in future changes in water availability in dry lands, and to investigate the thermodynamic and dynamic mechanisms that underpin future availability changesOfof water due to thesfeedbackk.

They found, in response to global warming, sharp decreases in surface water availability (precipitation minus evaporation, PE) in dry regions over oceans, but only a slight decrease in PE in dry landsOf Zhou suspected that this phenomenon is associated with earth-atmosphere processesOf “In dry lands, soil moisture is expected to decrease substantially with climate change,” he explainsOfChanges in soil moisture would further affect atmospheric processes and the water cycleOf”

Global warming is expected to reduce water availability and thus soil moisture in dry landsOf But this new study found that drying out of soil moisture actually negatively feeds back on water availability: decreased soil moisture reduces evapotranspiration and evaporative cooling, and improves surface warming in dry lands relative to humid regions and the ocean.

The contrast between global warming and the ocean reinforces the differences in air pressure between the ocean and the land, which generates increased wind and water vapor transport from ocean to land.

“Our work finds that the predictions of soil moisture and associated atmospheric reactions are highly variable and depend on the model – he highlights -OfThis study highlights the urgent need to improve future predictions of soil moisture and accurately represent thfeedbackk of soil and atmosphere moisture in models, which are critical to provide reliable predictions of water availability in dry lands for better management of water resourcesOf”

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