An observation-driven framework for modeling post-fire hydrologic response: evaluation for two central California case studies

Authors: LAHMERS, T - Goddard Space Flight Center; KUMAR, S - Goddard Space Flight Center; AHMAD, S - Goddard Space Flight Center; HOLMES, T - Goddard Space Flight Center; GETIRANA, A - University Of Maryland; ORLAND, E - Goddard Space Flight Center; LOCKE, K - Goddard Space Flight Center; BISWAS, N - Goddard Space Flight Center; NIE, W - Johns Hopkins University; PFLUG, J - Goddard Space Flight Center; WHITNEY, K - Goddard Space Flight Center; Anderson, Martha; YANG, YUN - Mississippi State University

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2025
Publication Date: 2/22/2025
Citation: Lahmers, T.M., Kumar, S.V., Ahmad, S., Holmes, T., Getirana, A., Orland, E., Locke, K., Biswas, N., Nie, W., Pflug, J., Whitney, K., Anderson, M.C., Yang, Y. 2025. An observation-driven framework for modeling post-fire hydrologic response: evaluation for two central California case studies. Water Resources Research. 61(2). Article e2023WR036582. https://doi.org/10.1029/2023WR036582.
DOI: https://doi.org/10.1029/2023WR036582

Interpretive Summary: Wildfires, which are an important physical process for ecosystems and the land surface, are increasing in frequency in a warming climate. Fires can also cause local changes to the water cycle over affected areas, sometimes leading to an increased likelihood of flooding and soil mass-movements. The time period of recovery of ecosystems after a fire remains an active area of research due to limited ground measurements. To address these challenges, models are needed to simulate the impacts of wildfire on local hydrology and the chance for flooding. This work presents a methodology that accounts for the impacts of post-fire vegetation and soil disturbances in a gridded model that quantitatively simulates changes to land surface states (e.g., soil moisture) and fluxes (e.g., evaporation and runoff) for a defined land area over time. For vegetation disturbances, we combine remote sensing-based vegetation data with model state variables to account the effects of fire. For soils, we develop an ensemble-based approach that increases soil runoff following fires, through an adjustment to land surface parameters within the model. Using these methods, we analyze the relative roles of vegetation and soil disturbances after fires in two case studies on runoff and evapotranspiration. Our results show the potential for remote sensing data and model parameter adjustment to resolve the effects of fires in simulations and improve decision making regarding post-fire response.

Technical Abstract: In a warming climate, wildfires are becoming increasingly common, especially in semi-arid environments like the western U.S. Wildfires can disrupt forest ecosystems and induce changes to the land surface. These collective impacts can alter the hydrologic response of a catchment following a fire, resulting in increased potential for surface runoff, reduced evapotranspiration, and ultimately a higher risk for flash flooding and mass wasting. The timescale of post-fire recovery of hydrological processes to return to pre-fire conditions is not well established due to the lack of ground measurements. Accurate characterization of the impacts of fire on hydrologic response and flooding is also challenging to simulate with models, given the complex interplay of various processes. Here we present a generalized modeling framework to quantify the impacts of wildfire on runoff generation. We consider the disturbance in the vegetation and soil as the two main factors contributing to post-fire floods. Using an ensemble modeling structure to acknowledge parameter uncertainty, remotely sensed Leaf Area Index (LAI) is assimilated into a land surface model (to simulate vegetation disturbance), and the maximum surface saturated fraction model parameter is decreased (to capture impacts of fire on soil hydrophobicity) following observed fires. We consider the impacts of resolving these processes on hydrologic states like runoff and evapotranspiration for two case-studies. Analysis of two events over Central California shows 1) the LAI assimilation has a greater impact on water balance and 2) the soil scheme captures a range of outcomes, where impacts on surface runoff that affect flood potential can be substantial.