As we expand our understanding of climate change, scientists have begun to focus on the growing role warming temperatures are playing as a potent driver of greater aridity–which is different than drought.

As NOAA describes it, drought is “a period of abnormally dry weather sufficiently long enough to cause a serious hydrological imbalance”. Aridity is measured by comparing long-term average water supply (precipitation) to long-term average water demand (evapotranspiration)…aridity is permanent, while drought is temporary.

A recent study from the University of Michigan and Colorado State reveals that aridity is already a clear trend across the western United States and human-caused warming is also driving increased aridity eastward across North America, with no end in sight.

Why This Matters: As study co-author Jonathan Overpeck explained,

“The impact of warming on the West’s river flows, soils, and forests is now unequivocal. There is a clear longer-term trend toward greater aridification, a trend that only climate action can stop.”

Increasing aridity doesn’t just affect an isolated region, it has the ability to disrupt precipitation patterns and ecosystems in nearby regions as well. The threats climate change already poses are being compounded by aridity and the only way to slow this trend is to take drastic action on climate change.

Why is Increasing Aridity a Problem? Aridity drives water scarcity and can wreak havoc on soils and their ability to produce crops by altering soil bacteria.

As Phys explained, aridity in the Western United States is typically framed in terms of episodic drought.

• Many water and land managers, as well as the general public, implicitly assume that when returning rains and snowfall break a long drought, arid conditions will also fade away. But that’s not the case if Western states.
• Additionally, warmer air can hold more water vapor, and this thirsty air draws moisture from water bodies and land surfaces through evaporation and evapotranspiration—further drying soils, stressing plants and reducing streamflow.
• But the atmosphere’s increased capacity to hold water vapor also boosts the potential for precipitation; rain and snow amounts are, in fact, rising in many regions of the United States outside the Southwest.
• However, the frequency and intensity of dry spells and droughts are expected to increase across much of the continent in coming decades, even if average annual precipitation levels rise

But in the West specifically, warming is also contributing to widespread tree death and more severe wildfires. 

Real Time: As Weather.com reported, despite a rainy April for Southern California, Northern California’s snowpack continues to thin while the ongoing drought worsens.

• The amount of water being held in the snowpack in the Sierra Nevada range is now below 40%, according to the California Department of Water Resources.

Additionally, America’s longest river was recently drier than during the Dust Bowl. And it’s bound to happen again.