Desert-like behaviors coming to world’s wet regions

Climate change is making historically wet and temperate areas behave more like deserts, a new study has found.

By the end of the century, the researchers project that an additional global area about twice the size of the United States will experience soil temperatures and moisture levels equivalent to today’s arid regions. 

A better understanding of these processes will be key to helping societies in these transitioning ecosystems adapt, according to the study, published on Monday in the journal Nature.

That means delving into a blind spot in current climate projections, co-author Heather Throop of Arizona State University said in a statement.

Something that “our models can’t take into account is: what if the rules by which the system works change?” Throop asked.

That’s an increasingly urgent question. Over the next century, such changes will come to wide areas, her team found. Desert-like conditions — high soil temperatures and minimal soil moisture — will come to define a vast area of currently wet and temperate areas, the team from Arizona State University and Israel’s Hebrew University found. 

These ecosystems are changing in long-term ways in response to a world where heat and drought are rapidly becoming more extreme. The two hottest years on record were 2016 and 2020, and nineteen of the hottest years on record have occurred since 2000, according to NASA. Extreme droughts are also expected to increase in size, area and frequency, the Nature study found.

Most hot spots for these conditions are in the North American boreal forest and the tropical rainforest of Southeast Asia, South America and Equatorial Africa — whose humid biospheres harvest repositories both of biodiversity and, therefore, carbon.

Talk about climate change often refers to a change in weather conditions, like a greater incidence of drought or hurricanes or fires. 

However, the new research goes beyond this, looking at how ecosystems function over the long term — how adaptations help life survive as conditions of relative abundance change to conditions of hardship and scarcity. 

In a humid forest, for example, ecosystems depend on cool temperatures and plentiful water. The canopy and the soil are constantly competing for moisture; trees are adapted to low levels of rain and a rich layer of plants, insects and microbes that break down detritus and the dead bodies of plants and animals.

In dryland environments, by contrast — deserts, prairies, steppes, dry forest and savannah — the punishing sun and wind drives a world of scarce resources and boom and bust ecology, the scientists found. 

With rain coming in rare pulses, and a landscape that heat and dry air have baked into water-repelling clays, life has to adapt to conditions of scarcity, broken by occasional periods of dangerous abundance.

In these environments, the sun and wind, not insects and microbes, break down organic waste. With less rain, plants and leaf litter make use of dew and ambient moisture in the air. Air moving beneath an oak canopy cools the land, not the evaporation from water off of evergreen leaves. Deep rooted plants secure water and nutrients within the soil.  

In one subtle but important transition, as landscapes become too hot and dry for grasses and shrubs to survive, the foundation of the ecosystem shifts from plants to thin “crusts” of bacteria and lichens — which work carbon and nutrients into the soil. 

These ecosystem dynamics have been traditionally neglected in favor of the rules that govern the temperate regions where most people live — and where, historically, most of the world’s resource universities have been.

The Nature study suggests that neglect is no longer sustainable. “These new insights can contribute to advancing our adaptive capacity to withstand climate extremes and lessen their impacts on nature and people,” Throop said.