Watersheds dynamics following wildfires: Nonlinear feedbacks and implications on hydrologic responses

Abstract

In recent years, wildfires in the western United States have occurred with increasing frequency and scale. Climate change scenarios in California predict prolonged periods of droughts with even greater potential for conditions amenable to wildfires. The Sierra Nevada Mountains provide 70% of water resources in California, yet how wildfires will impact watershed-scale hydrology is highly uncertain. In this work, we assess the impacts of wildfires perturbations on watershed hydrodynamics using a physically based integrated hydrologic model in a high-performance-computing framework. A representative Californian watershed, the Cosumnes River, is used to demonstrate how postwildfire conditions impact the water and energy balance.Results from the high-resolution model show counterintuitive feedbacks that occur following a wildfire and allow us to identify the regions most sensitive to wildfires conditions, as well as the hydrologic processes that are most affected. For example, whereas evapotranspiration generally decreases in the postfire simulations, some regions experience an increase due to changes in surface water run-off patterns in and near burn scars. Postfire conditions also yield greater winter snowpack and subsequently greater summer run-off as well as groundwater storage in the postfire simulations. Comparisons between dry and wet water years show that climate is the main factor controlling the timing at which some hydrologic processes occur (such as snow accumulation) whereas postwildfire changes to other metrics (such as streamflow) show seasonally dependent impacts primarily due to the timing of snowmelt, illustrative of the integrative nature of hydrologic processes across the Sierra Nevada-Central Valley interface. K E Y W O R D S climate extremes, integrated hydrologic model, vegetation changes, water management, watershed dynamics, wildfires

The Role of Subsurface Flow on Evapotranspiration: A Global Sensitivity Analysis

“…Land use and land cover (LULC) was chosen to be heterogeneous and is based on the real‐world spatial distribution of a region located near the city of Sacramento in northern California, USA. This region was selected given its heterogeneous distribution of different LULC types, typical of many mixed‐land environments, including wetland, cultivated lands, pasture, grasslands, and open space (Maina et al, 2020; Maina & Siirila‐Woodburn, 2019). The northern section of the model was homogeneously classified as evergreen forestland to provide additional insights into this LULC environment (see Figure 1).…”

Simulating fully-integrated hydrological dynamics in complex Alpine headwaters: potential and challenges

“…Penn et al (2016) altered vegetation parameters in a ParFlow.CML model to assess the hydrological impacts of mountain pine beetle-induced tree mortality in another Coloradoan headwaterthat of the Big Thompson River, while Carroll et al (2019) developed a GSLOW model of the entire East River, Colorado, finding groundwater to be an important and stable contributor to mountain streamflow. Finally, Maina & Siirila-Woodburn (2020) investigated hydrological responses following fire dynamics in a Californian watershed spanning a considerable elevational range using ParFlow.CLM.…”

Megafire affects stream sediment flux and dissolved organic matter reactivity, but land use dominates nutrient dynamics in semiarid watersheds

“…At the same time that wildfires are growing in size and severity throughout the U.S., precipitation is becoming more intense due to anthropogenic climate change and land use, with longer periods of water scarcity followed by intense storm events [ 6 , 7 , 44 – 46 ]. Together, these changes in disturbance regime threaten ecosystem function and human well-being by creating synchronous disturbances such as drought, flood, wildfire, and pollutant flux that affect large areas, potentially degrading habitat rather than restoring it [ 47 – 50 ]. Understanding how ecosystems in different biomes and human contexts respond to multiple stressors such as wildfire and extreme precipitation is crucial to support ecosystem integrity and services in the face of novel disturbance regimes [ 51 – 54 ].…”

“…After a wildfire, the decrease in transpiration and increase in soil hydrophobicity can augment peak flows during storm events, which increases the frequency of flooding [ 41 , 56 , 62 ]. At small scales (e.g., catchments smaller than 100 km 2 ), this generally results in higher runoff ratios and lower groundwater recharge during precipitation events [ 52 , 63 ], though observed responses range widely depending on local conditions [ 4 , 50 , 64 ]. At larger scales (e.g.…”