photo credit: CAL FIRE

Overview

In addition to increasing wildfire hazard, the warmer and drier conditions associated with climate change are also exacerbating long-standing water security issues for the Northern California region. Much of the region depends on small local surface water and groundwater systems for community and agricultural water use. Recently, severe droughts have led to extensive tree mortality, reduced forage production for grazing animals, and limited freshwater resources for people and wildlife.

Conflict over water use rights is a long-standing issue in the region. Historically, agricultural water demands have been pitted against water for wildlife because regulations require that tributaries release specified amounts of water to sustain endangered fish and other aquatic wildlife, thus diminishing water supplies available to irrigate crops and livestock. This historic conflict has not been resolved, and now many Northern California communities are additionally concerned about the allocation of water resources for fire protection. Because wildfires in the region generally occur during the dry summer season when water resources are scarce, regional stakeholders perceive an increasing need to increase local water storage capacity and recharge groundwater reservoirs to have water resources available for fire fighting.

Despite these challenges, many organizations and collaborations across the regions are working toward solutions that increase community resilience to wildfire while also restoring the ecological health of watersheds. The health of the region’s fisheries have evolved to be tied to having healthy fire on the landscape, and Indigenous people helped to cultivate this balance. For example, smoke from cultural burning was understood to benefit cold-water adapted fish, such as salmon and steelhead, by cooling river and stream temperatures during the summer. A recent study provides modern evidence of this phenomenon occurring by showing that wildfire smoke significantly reduced both maximum and mean water temperature in the Klamath River Basin.

Many other forest management practices that mitigate wildfire hazard can also benefit watershed health. For example, thinning overly-dense forests can promote the health of the remaining plants by reducing competition for limited water resources. This has also been observed to result in more water in streams that previously ran dry. By reducing fuels and soil moisture deficit, these practices also mitigate the risk of high-severity fire burning soil and causing significant canopy cover loss, thus preventing erosion-caused sedimentation and warmer water temperatures that are detrimental to fish populations.

Stakeholder Perspectives

Survey respondents rated securing water supply for residential use as the highest priority area of investment for achieving this outcome. Actions that increased watershed health, including ecosystem restoration, addressing water pollution impacts to humans and ecosystems, and reducing soil erosion, were also considered to be highly important. Reducing regulatory barriers was considered to be less important for water security. Public survey responses ranged widely regarding the importance of securing water supply for economic use and addressing constraints related to water rights, though interviewees indicated that these were key issues in the region that are being exacerbated by climate change and increasing wildfire hazard.

Resource Conditions

Water security can be assessed in terms of actual evapotranspiration/precipitation (AET Fraction) (top) and annual mean runoff (bottom). Actual evapotranspiration is the combined amount of water that evaporates from the land surface in addition to the water that is lost as vapor from plants. AET Fraction represents the percentage of water needed by plants that is met by precipitation during a severe 4-year drought. This metric is important for water security because it estimates the moisture stress that would be experienced by the vegetation during drought. Values > 1 indicate moisture stress driven by shortfalls in precipitation relative to plant needs. Values < 1 indicate no water stress. Both vegetation management and disturbances like wildfire can affect AET Fraction by reducing the amount of vegetation at a site and thereby lowering the amount of water needed by plants. Annual mean runoff is the surplus water discharged from a location in the form of surface or groundwater flows. This metric is important for water security because it estimates the amount of surplus water for downstream use. Vegetation management and disturbances like wildfire can affect runoff in part by changing the vegetation conditions at a site. For example, forest treatments that thin trees in moisture-stressed areas may increase runoff and provide more water availability downstream.