Cumulative effects of fire and drought in Mediterranean ecosystems

Ecological Society of America (ESA) | August 18th, 2017

The occurrence of multiple disturbances can jointly affect the recovery capacity of ecosystems, potentially leading to changes in vegetation dynamics or loss of resilien

The occurrence of multiple disturbances can jointly affect the recovery capacity of ecosystems, potentially leading to changes in vegetation dynamics or loss of resilience. The effects of interacting disturbances on ecosystems are, however, not well understood. We use a model system based on Mediterranean-type ecosystems (MTEs) to examine how the interplay between vegetation regeneration traits andcompound, stochastic disturbances modulate ecosystem dynamics. We developed a state-and-transition simulation model including two tree species with contrasting regeneration strategies (seeder vs. resprouter) and a shrub-land formation. We aim to assess potential compositional switches under contrasted scenarios of compound fire–drought regimes, and to characterize the cumulative effects of fire–drought(synergism vs. antagonism) relative to the effects of individual disturbance regimes. Our simulation results indicate that interaction between moderate fire and sporadic drought recurrence—as opposed to chronic dryness—can act as a strong mechanism generating highly heterogeneous landscapes in which different regeneration types coexist, as observed in MTEs. Resprouters dominated under individual, moderate disturbance regimes of fire or drought, whereas the interaction of the two disturbances promoted the long-term coexistence of both tree regeneration strategies. However, shrub-land expansion and persistence at the expanse of forests was favored by increases in drought recurrence and associated fire–drought interactions, highlighting the potential for important vegetation changes in MTEs under climate change. Overall, the cumulative effects of fire and drought can lead to distinct landscape configurations under moderate disturbance regimes that are otherwise only attained under high frequency of individual disturbances. At the ecosystem level, however, we suggest that disturbance-induced vegetation dynamics can modify vegetation sensitivity and resilience to further disturbances precluding the prevalence of synergistic effects of the two disturbances.

Debris flow occurrence under changing climate and wildfire regimes: A southern California perspective

Geomorphology (Elsevier) | December 2nd, 2022

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large s

In southern California, wildfire incidents are increasing in frequency and magnitude. There is a great deal of research predicting the impact of climate change on large scale fire regimes. These impacts, now the new normal, include increases in future fire incidents and burn severities. Yet predictive studies on how ecosystems respond to changing fire regimes are lacking. Identifying trends in post-fire erosion patterns, such as post-fire debris flows, is critical for increasing human resiliency and adaptation to changing weather patterns and eventual long-term climate change. The relative historical abundance of post-fire debris flows in southern California presents this concern: will worsening wildfire regimes result in more post-fire debris flows? Our research addresses this concern by utilizing a descriptive approach to analyze post-fire debris flows in southern California from 2001 to 2018 to elucidate possible trends. We found that 84 % of debris flows originate from watersheds with soils burnt at moderate soil burn severity. We found that debris flow occurrence is more reliant on the percent coverage of a soil burn severity classification than its areal extent. Further, larger fires also tended to produce more debris flows and most (73 %) debris flow watersheds occurred in predominantly bedrock areas. Our research suggests that the number of post-fire runoff-generated debris flows in the region will increase if fires continue to increase in size, occur on slopes of at least 20°, burn south-facing watersheds with bedrock of igneous or sedimentary origin to at least a moderate severity, and peak rainfall intensity return intervals do not change. These findings highlight the interconnectivity between natural erosive processes, wildfires, humans, and climate change.

Decision on Petition for Rulemaking to Set Permanent Minimum Flows on the Shasta River

California State Water Resources Control Board (SWRCB) | February 16th, 2024

Declines in Peak Snow Water Equivalent and Elevated Snowmelt Rates Following the 2020 Cameron Peak Wildfire in Northern Colorado

American Geophysical Union (AGU) | March 28th, 2023

The loss of tree canopy greatly increases the amount of solar energy that reaches the snow surface. Soot and debris from burned trees make the snow surface darker, result

The loss of tree canopy greatly increases the amount of solar energy that reaches the snow surface. Soot and debris from burned trees make the snow surface darker, resulting in more of this energy being absorbed. Late-season snow storms were able to temporarily counteract some of these effects by burying the darker snow surface. As more and more of the western United States is fire-impacted, it is essential to better understand and account for these impacts on this critical water reservoir for this region.

Declining Freshwater Availability in the Colorado River Basin Threatens Sustainability of Its Critical Groundwater Supplies

American Geophysical Union (AGU) | May 27th, 2025

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico

Climate change is causing more frequent and intense droughts around the world, including in the Colorado River Basin, which supplies water to seven U.S. states and Mexico, and is facing severe water shortages. This study investigates how changes in water storage components (e.g., snow, surface water, soil moisture and groundwater) and water use are contributing to these shortages, and impacting agriculture and municipal water supplies, using data from the NASA GRACE and GRACE Follow-On (GRACE-FO) satellite missions, land surface models, and in situ data over the past two decades. Results show significant losses of groundwater: 7.8.0 ± 5.3 km3 in the Upper CRB (UCRB) and 25.5 ± 7.4 km3 in the Lower CRB (LCRB). Progress toward sustainable groundwater could be achieved by reducing groundwater extraction, in line with current rates of depletion (0.35 km3 in the UCRB and 1.15 km3 in the LCRB). This research highlights the importance of understanding the factors affecting groundwater levels to create sustainable water management strategies that can help secure water resources for the region's future.

Declining groundwater storage expected to amplify mountain streamflow reductions in a warmer world

Nature Portfolio (Springer Nature) | May 23rd, 2024

Groundwater interactions with mountain streams are often simplified in model projections, potentially leading to inaccurate estimates of streamflow response to climate ch

Groundwater interactions with mountain streams are often simplified in model projections, potentially leading to inaccurate estimates of streamflow response to climate change. Here, using a high-resolution, integrated hydrological model extending 400 m into the subsurface, we find groundwater an important and stable source of historical streamflow in a mountainous watershed of the Colorado River. In a warmer climate, increased forest water use is predicted to reduce groundwater recharge resulting in groundwater storage loss. Losses are expected to be most severe during dry years and cannot recover to historical levels even during simulated wet periods. Groundwater depletion substantially reduces annual streamflow with intermittent conditions predicted when precipitation is low. Expanding results across the region suggests groundwater declines will be highest in the Colorado Headwater and Gunnison basins. Our research highlights the tight coupling of vegetation and groundwater dynamics and that excluding explicit groundwater response to warming may underestimate future reductions in mountain streamflow.

Declining mountain snowpack in western North America

American Meteorological Society (AMS) | January 3rd, 2005

Mountain snowpack in western North America is a key component of the hydrologic cycle, storing water from the winter (when most precipitation falls) and releasi

Mountain snowpack in western North America is a key component of the hydrologic cycle, storing water from the winter (when most precipitation falls) and releasing it in spring and early summer, when economic, environmental, and recreational demands for water throughout the West are frequently greatest. In most river basins of the West, especially in Washington, Oregon, and California, snow (rather than man-made reservoirs) is the largest component of water storage; hence, the West is (to varying degrees) vulnerable to climatic variations and changes that influence spring snowpack.

Delta Conveyance Project: Modernizing California’s Water Infrastructure, Fast Facts 2024

California Department of Water Resources (DWR) | September 13th, 2023

DRAFT Staff Report/Substitute Environmental Document in Support of Potential Updates to the Water Quality Control Plan for the San Francisco Bay/Sacramento-San Joaquin Delta Estuary for the Sacramento River and its Tributaries, Delta Eastside Tributaries, and Delta

California State Water Resources Control Board (SWRCB) | September 28th, 2023

Droughts impede water balance recovery from fires in the Western United States

Nature Portfolio (Springer Nature) | January 2nd, 2024

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and

A steady rise in fires in the Western United States, coincident with intensifying droughts, imparts substantial modifications to the underlying vegetation, hydrology and overall ecosystem. Drought can compound the ecosystem disturbance caused by fire, although how these compound effects on hydrologic and ecosystem recovery vary among ecosystems is poorly understood. Here we use remote sensing-derived high-resolution evapotranspiration (ET) estimates from before and after 1,514 fires to show that ecoregions dominated by grasslands and shrublands are more susceptible to drought, which amplifies fire-induced ET decline and, subsequently, shifts water flux partitioning. In contrast, severely burned forests recover from fire slowly or incompletely, but are less sensitive to dry extremes. We conclude that moisture limitation caused by droughts influences the dynamics of water balance recovery in post-fire years. This finding explains why moderate to extreme droughts aggravate impacts on the water balance in non-forested vegetation, while moisture accessed by deeper roots in forests helps meet evaporative demands unless severe burns disrupt internal tree structure and deplete fuel load availability. Our results highlight the dominant control of drought on altering the resilience of vegetation to fires, with critical implications for terrestrial ecosystem stability in the face of anthropogenic climate change in the West.