Weakening mechanisms imposed on California’s levees under multiyear extreme drought

California is currently suffering from a multiyear extreme drought and the impacts of the drought are anticipated to worsen with climate change. The resilience of California’s critical infrastructure such as earthen levees under drought conditions is a major concern that is poorly understood. California maintains more than 21,000 km of urban and nonurban levees which protect dry land from floods and deliver two-thirds of the state’s drinking water. Many of these levees are currently operating under a high failure risk condition. This essay argues that California’s protracted drought can further threaten the integrity of these already at-risk levee systems through the imposition of several thermo-hydro-mechanical weakening processes. Pertinent facts and statistics regarding California’s drought and current status of its levees are presented. Lessons from previous catastrophic levee failures and major damages which occurred under similar events are discussed. Weakening processes such as soil-strength reduction, soil desiccation cracking, land subsidence and surface erosion, and microbial oxidation of soil organic carbon are comprehensively evaluated to illustrate the adverse impacts that the ongoing California drought can have on levees. This essay calls for further research in light of these potential drought-induced weakening mechanisms to support adaptation and mitigation strategies to possibly avert future levee failures. These weakening processes can threaten any drought-stricken infrastructure interfacing with soil, including embankments, roads, bridges, building foundations, and pipelines.