Extreme rain over California’s burn scars causes mudslides: This is what cascading climate disasters look like

Two powerful storm systems known as atmospheric rivers are heading for northern California and Oregon, a region in the midst of an historic drought.

While the storms will bring much-needed water to a parched region and should significantly lower the , they also bring dangerous new flood and mudslide risks, particularly in areas recovering from wildfires.

Wildfires strip away vegetation and leave the soil less able to absorb water. A downpour on these vulnerable landscapes can quickly erode the ground as fast-moving water carries debris and mud with it.

The National Weather Service has warned of ash and debris flows from Oct. 21–26 in several burned areas, including the site of the nearly 1-million-acre Dixie Fire in the Sierra Nevada.

I study cascading hazards like this, in which consecutive events lead to human disasters. Studies show climate change is raising the risk of multiple compound disasters, and it’s clear that communities and government agencies aren’t prepared.






Video shows how quickly a mudslide overtakes a town.

When storms hit burn scars

California has experienced this kind of cascading disaster before.

In early 2017, following years of , the region had a wet winter that fueled dense growth of vegetation and shrubs. An unusually warm and dry spring and summer followed, and it dried out the vegetation, turning it into fuel ready to burn. That fall, extreme Santa Ana and Diablo winds—known for their sustained low humidity—created the perfect conditions for wildfires.

The Thomas Fire began near Santa Barbara in December 2017 and burned over 280,000 acres. The following January, hit the region, including the burn scar left by the fire, and caused the deadliest mudslide-debris flow event in California’s history. More than 400 homes were destroyed in about two hours, and 23 people died.

These kinds of cascading events aren’t unique to California. Australia’s Millennium Drought (1997–2009) also ended with devastating floods that inundated urban areas and breached levees. A study linked some of the levee and dike failures to earlier drought conditions, such as cracks forming because of exposure to heat and dryness.

Individually, they might not have been disasters

When multiple hazards, such as droughts, , wildfires and extreme rainfall, interact, human disasters often result.

Author sundquistassociates Posted on July 28, 2021Categories Earth

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