Modeling Wildfire Effects on Ecosystem Services in two Disparate California Watersheds and Communities

Abstract

Ecosystem services are important for human well-being and for sustaining environmental quality objectives. Growing concern over extreme wildfire events in various watersheds necessitates understanding their impacts on regulating ecosystems services. Past studies have documented how wildfires regulate ecosystem services, but the distributional impacts of such ecosystem services across various human settlements (i.e. communities) remains understudied, despite renewed focus on how they are increasingly at risk from and being impacted by wildfires. We used the Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model to examine how two wildfires that occurred in California, USA in 2017 impacted water provisioning, soil loss and sediment delivery, carbon sequestration services, and nutrient delivery in two watersheds and their respective communities. Regression analyses were used to determine the differences in the distribution of ecosystem services before and after the fires, and whether these wildfires exacerbated the differences in impacts to ecosystem services across communities in the watershed. We find that a year following the fires, the amount of biomass in forestland, woodland, and chaparral declined in both studied watersheds, while the amount of grassland increased. The model revealed that the changes in vegetation resulted in losing about 200,000 tons of carbon from the Mark West subwatershed and about 160,000 tons of carbon from the southern California watersheds. The expected mean annual water yield for both watersheds increased by 5% and 42%, respectively post-fire. Expected post-fire phosphorus and nitrogen export also increased. Finally, we found evidence of human community-level differences in the distribution of pre-fire ecosystem services but no evidence that post-fire conditions either exacerbated or alleviated these impacts.

Keywords: InVEST model; Regulating ecosystem services; Socio-demographics; Soil carbon; Thomas Fire; Tubbs Fire; Wildfire impacts.

Fig. 1

Map of the study area with land cover types

Fig. 2

The figure shows the difference in annual water yield (mm) before and after the fire in the Mark West (left) and southern California watersheds (right)

Fig. 3

The figure shows the difference in soil loss (tons ha⁻¹ year⁻¹) before and after the fire in the Mark West (left) and southern California watersheds (right)

Fig. 4

The figure shows the difference in sediment export (tons ha⁻¹ year⁻¹) before and after the fire in the Mark West (left) and southern California (right) watersheds

Fig. 5

The figure shows the difference in nitrogen export (kg ha⁻¹ year⁻¹) before and after the fire in the Mark West (left) and southern California watersheds (right)

Fig. 6

The figure shows the difference in phosphorus export (kg ha⁻¹ year⁻¹) before and after the fire in the Mark West (left) and southern California watersheds (right)

Fig. 7

Nutrient dynamics in Mark West watershed

Fig. 8

Nutrient dynamics in southern California watershed