Integrating Remote and In-Situ Data to Assess the Hydrological Response of a Post-Fire Watershed

Abstract

Forest fire is a common concern in Mediterranean watersheds. Fire-induced canopy mortality may cause the degradation of chemical–physical properties in the soil and influence hydrological processes within and across watersheds. However, the prediction of the pedological and hydrological effect of forest fires with heterogenous severities across entire watersheds remains a difficult task. A large forest fire occurred in 2017 in northern Italy providing the opportunity to test an integrated approach that exploits remote and in-situ data for assessing the impact of forest fires on the hydrological response of semi-natural watersheds. The approach is based on a combination of remotely-sensed information on burned areas and in-situ measurements of soil infiltration in burned areas. Such collected data were used to adapt a rainfall–runoff model over an experimental watershed to produce a comparative evaluation of flood peak and volume of runoff in pre- and post-fire conditions. The model is based on a semi-distributed approach that exploits the Soil Conservation Service Curve Number (SCS-CN) and lag-time methods for the estimation of hydrological losses and runoff propagation, respectively, across the watershed. The effects of fire on hydrological losses were modeled by adjusting the CN values for different fire severities. Direct infiltration measurements were carried out to better understand the effect of fire on soil infiltration capacity. We simulated the hydrological response of the burned watershed following one of the most severe storm events that had hit the area in the last few years. Fire had serious repercussions in regard to the hydrological response, increasing the flood peak and the runoff volume up to 125% and 75%, respectively. Soil infiltration capacity was seriously compromised by fire as well, reducing unsaturated hydraulic conductivity up to 75% compared with pre-fire conditions. These findings can provide insights into the impact of forest fires on the hydrological response of a whole watershed and improve the assessment of surface runoff alterations suffered by a watershed in post-fire conditions.

Unusual late-fall wildfire in a pre-Alpine Fagus sylvatica forest reduced fine roots in the shallower soil layer and shifted very fine-root growth to deeper soil depth

“…A 243-ha wildfire burned on southern aspects in late October—early November 2017 after leaves had senesced. In-situ post-fire surveys revealed a range of fire intensities and subsequent effects on soil and understory and overstory vegetation 41 .…”

“…We selected eight fire-affected and eight control (unburned) beech trees from, respectively, a moderate burn severity area 41 and an unburned area about 500–1000 m apart at comparable elevations (Fig. 1 ; ~ 1100 m a.s.l.…”

“…Average slope is ~ 46%. The thin, clay-loamy soil 41 is a leptic and eutric Cambisol 42 , 43 . We sampled trees one month after the wildfire (December 2017), in May, July, and October of 2018, and in July 2019.…”

Best practices in post-flood surveys: The study case of Pioverna torrent

“…The meteorological stations measured a cumulative rainfall in 13 hours, ranging between 41.4 mm (station 8097) and 83.0 mm (station 9105), except for the station 19335, which recorded 209.2 mm (Figure 2B). The corresponding return periods, estimated through the moving-window procedure for detecting the maximum rainfall depth observed for each duration (Norbiato et al, 2007) and then the Depth-Duration-Frequency curve (Folador et al, 2021), were approximately 4 years, except for the observations of station 19335 that registered a 300-years return period events. This fact was in accordance with the losses suffered (yellow dots in Figure 1).…”

Evaluating Post-Fire Erosion and Flood Protection Techniques: A Narrative Review of Applications

“…Many studies provided evidence that the most severe sediment losses occurred within the first year after the wildfire [17][18][19]. However, the magnitude of the damages can vary depending on multiple factors, such as climate, fire frequency, soil type, geology, topography (especially slopes), and vegetation [20,21]. Regarding water quality, Rust et al [22] studied several sites in the western USA and found that nutrient flux (different forms of nitrogen and phosphorus), major-ion flux, and metal concentrations are the most common pollutants in streams within the first five years after a wildfire.…”