unprecedented storm The storm that wreaked havoc across much of Southern California will eventually subside, possibly with much-needed rain to help. But emergency and public works crews may not have much time to rest: Any rainfall after the fires will bring a greater risk of mudslides and mudslides that will test the limits of the region's infrastructure.

Wildfires have burned vegetation on hillsides, while extreme heat has baked topsoil. On this altered landscape, even small amounts of rainfall can trigger massive amounts of runoff, which moves rapidly downward, eroding soil and debris and gathering it into a fast-moving mixture.

Depending on the amount of sediment, rock, and wood, these phenomena are called debris flows or debris flows. They are extremely dangerous to both property and people, and the risk can persist for years until vegetation regrows and soil recovers.

After a series of deadly and destructive post-fire floods in the 1930s, Southern California invested heavily in infrastructure to control such flows, particularly large dams and smaller debris basins designed to keep mud and debris hazards at bay. It reaches the mountains before reaching the more populated areas of the base. More than 150 trash basins have been built in Southern California and are the first line of defense for communities below the Santa Monica and San Gabriel Mountains, where the Palisades and Eaton Mountain fires burned.

But this infrastructure does not provide absolute protection. Smaller debris basins are prone to overflowing.

Rain after another winter fire, thomas fire Begun in December 2017 in the Santa Ynez Mountains above Ventura and Santa Barbara counties, creating some of California's deadliest flood Within a century. The debris flow, composed of water, dirt, boulders, brush and trees, surged out of a canyon in the Santa Ynez Mountains, spilled over the debris flow basin and traveled for miles, destroying parts of the town of Montecito and blocking the 101 highway. The floods killed 23 people and destroyed 400 buildings.

Maintaining debris basins—specifically, removing accumulated sediment so that they have enough capacity to handle the next storm—is critical to avoiding such tragedies. Clearing debris basins between storms is especially difficult and expensive because of saturated soils, but it can be especially important. Latest research from UC Irvine It has been shown that debris basins can overflow due to the cumulative effect of successive storms.

we are happy to see Governor Gavin Newsom’s Executive Order Government agencies are called on to prepare for mudslides and mudslide risks. Removing debris from burn areas will help minimize the volume of material that can cause debris flows, while clearing debris basins and floodways will help maximize the ability of these structures to protect communities. But policymakers must also provide the funding necessary to repeatedly clean flood control infrastructure throughout the year, rapidly update flood hazard maps to accurately reflect the severity of burns in watersheds, communicate risks to nearby residents and businesses, and provide prompt and efficient solutions in the event of flooding. Be prepared to evacuate. considered necessary.

Climate change is exacerbating California's fire and flood cycles, putting more people at risk and putting greater pressure on infrastructure designed for a different climate and a much smaller population. Just as wildfire danger is increasing, the risk of post-fire mudslides and mudslides is urgent and profound. It calls for immediate preparedness and public cooperation to save lives and protect communities.

Jeffrey Mount is a senior fellow at the Water Policy Center at the Public Policy Institute of California. Brett Sanders is professor of civil and environmental engineering, urban planning, and public policy at the University of California, Irvine.