8 February 2023

Climate and drought are the perfect recipe for disruption (not just) in California


During extended drought periods, soil loses its ability to absorb water, writes The New York Times. When rain occurs, landslide risk increases. A combination of phenomena that climate change makes increasingly frequent

by Matteo Cavallito


Drought, rain, fire and soil disruption. Four processes for a single vicious cycle that has long plagued California, a victim of the consequences of global warming. It is a troubling picture the one described in recent weeks by the New York Times. “After several years of intense drought, California is now being pummeled by weeks of heavy rain,” the US newspaper wrote a few days ago. “AAs the state’s residents are discovering, the two opposite meteorological conditions can combine to make for severe mudslides.”

During periods of prolonged water crisis, soils dry out and lose their drainage capacity. The result is a buildup of water on the surface and a gradual runoff of water capable of generating potentially destructive landslides. But this, off course, is not the only consequence of heat waves.

Drought, fires and landslides

“California’s drought has also helped fuel major wildfires in recent years, and post-wildfire slopes are especially susceptible to mudslides,” the U.S. newspaper writes. The destruction of plants caused by the flames eventually weakens the roots, thereby reducing soil stability. This phenomenon, combined with the decreased permeability of the soil increases water runoff during rainfall thus leading to an increased risk of landslides.

Landslides are commonly imagined as sudden events. But the truth is that land subsidence is sometimes progressive and occurs very slowly over years before rainfall accelerates the process.

“After the 2017 slide in Big Sur in Northern California that is considered the largest in state history, when about 6 million cubic yards of debris slid across Route 1, NASA researchers used radar data to study the slope,” the New York Times continues. “They found that it had been moving at a rate of about 7 inches a year for about a decade.”

Interaction of events causes disasters

Underlying natural disasters is often the simultaneous interaction of different phenomena. Some of them, the Australian network The Conversation wrote recently, would not be devastating on their own. But their combination can prove destructive. When a heat wave hits an area that has long been subject to drought, for example, the risk of wildfires increases. Climate change, at the same time, seems to be making these phenomena increasingly frequent and devastating.

By the end of 2020, said a research involving several U.S. and non-U.S. universities, the devastating wildfires in California caused colossal economic damage.

The state, the survey revealed, has suffered $102.6 billion in losses, between direct costs – starting with health care – and indirect costs such as impact to businesses. Indirect costs include $46 billion of additional damages related to the aftermath of the fires and recorded outside the state. This results in a total amount of $148.5 billion or about 0.7 percent of U.S. GDP.

Extreme events are becoming increasingly frequent

Evidence of the increasing incidence of extreme events is mounting. A recent study by the World Weather Attribution (WWA), a group of scientists formed to study the frequency of these events, found that the climate crisis had made the record drought that hit the Northern Hemisphere this summer at least 20 times more likely.

The latest report by the Global Water Monitor Consortium, an initiative of the Australian National University, also showed how global warming is altering the water cycle.

Drought and fire-risk conditions, as a result, are developing faster and more frequently. Also increasing, at the same time, is extreme precipitation concentrated in short periods. Two phenomena capable of combining causing obvious and dangerous consequences.