LANDIS-VELMA Model Linkage to Assess the Effects of Wildfire on Water Quality and Potential Benefits of Management Action to Protect Drinking Water Supply

Wildfires in western US forests increased over the last two decades, resulting in increased solids and nutrient loadings to streams, possibly threatening drinking water supplies. Wildland fires adversely affect water quality measures, especially organic matter concentrations requiring additional treatment resulting in formation of increased disinfection byproducts. Modeling influences of riparian biomass on watershed dynamics is essential to protect aquatic ecosystem health and drinking water quality by understanding interactions between climate, land use change, and complex hydrodynamic-biogeochemical processes. Eco-hydrologic models, such as Visualizing Ecosystems for Land Management Assessments (VELMA), are applied to simulate the effects of disturbances including burned watersheds. VELMA is a model that utilizes land surface hydrology and terrestrial biogeochemistry for simulating the integrated responses of vegetation, soil, and water resources to changes in climate, land use, land cover, and disturbance. LANDIS-II, the forest landscape model, is similarly multi-scale grid-based and simulates changes in forests cohort succession and disturbance over centuries across large areal extents. Linking LANDIS and VELMA integrates the strengths of both models, providing unique capabilities for linking spatial and temporal dynamics of fire spread and fuel consumption (LANDIS-II), with the ability to simulate multi-scale hydrological and biogeochemical controls on water quality and quantity dynamics (VELMA). The Hayman Fire of 2002, one of the largest and most devastating wildfires in Colorado's recorded history, served as the study area for the LANDIS-VELMA model linkage. The best simulation indicates a NSE of 0.62 during the years of 2000 to 2006 with best annual performance of 0.96 in the year 2006 in Brush Creek using LANDIS biomass and age estimates only differing by a maximum of 5.86% in comparison to other biomass models. Annual evapotranspiration (AET) comparisons from NLDAS estimates best performance occur during 2004 to 2006. 52.6% of VELMA modeled precipitation during the disturbance interval were equivalent to NLDAS and PRISM. Elevated concentrations of nutrient loss and delineated pools are observed in both VELMA and ground observations during the disturbance interval.