Assessing the hydrologic response to wildfires in mountainous regions

Abstract

Abstract. This study aims to understand the hydrologic responses to wildfires in mountainous regions at various spatial scales. The Soil and Water Assessment Tool (SWAT) was used to evaluate the hydrologic responses of the upper Cache la Poudre Watershed in Colorado to the 2012 High Park and Hewlett wildfire events. A baseline SWAT model was established to simulate the hydrology of the study area between the years 2000 and 2014. A procedure involving land use and curve number updating was implemented to assess the effects of wildfires. Application of the proposed procedure provides the ability to simulate the hydrologic response to wildfires seamlessly through mimicking the dynamic of the changes due to wildfires. The wildfire effects on curve numbers were determined comparing the probability distribution of curve numbers after calibrating the model for pre- and post-wildfire conditions. Daily calibration and testing of the model produced “very good” results. No-wildfire and wildfire scenarios were created and compared to quantify changes in average annual total runoff volume, water budgets, and full streamflow statistics at different spatial scales. At the watershed scale, wildfire conditions showed little impact on the hydrologic responses. However, a runoff increase up to 75 % was observed between the scenarios in sub-watersheds with high burn intensity. Generally, higher surface runoff and decreased subsurface flow were observed under post-wildfire conditions. Flow duration curves developed for burned sub-watersheds using full streamflow statistics showed that less frequent streamflows become greater in magnitude. A linear regression model was developed to assess the relationship between percent burned area and runoff increase in Cache la Poudre Watershed. A strong (R2 > 0.8) and significant (p < 0.001) positive correlation was determined between runoff increase and percentage of burned area upstream. This study showed that the effects of wildfires on hydrology of a watershed are scale-dependent. Also, using full streamflow statistics through application of flow duration curves revealed that the wildfires had a higher effect on peak flows, which may increase the risk of flash floods in post-wildfire conditions.

Assessing the adequacy of SWAT model to simulate postfire effects on the watershed hydrological regime and water quality

“…The crop vegetation factor (C) was modified to 0.2, 0.05, and 0.01 (−), for, respectively, high, moderate, and low burn severity (Larsen & MacDonald, 2007). The CN was increased by 15, 10, and 5 (−) for high, moderate, and low severity, respectively (Havel, Tasdighi, & Arabi, 2018). Those changes were introduced to the SWAT database, creating new land use and soil classes for each level of severity (Figure 3).…”

Heterogeneity in Event-Based Soil Hydrologic Response to Different Land Use Types in Upper River Njoro Catchment, Kenya

“…The Upper River Njoro Catchment, Kenya flow paths can change as a result of soil compaction during deforestation. As indicated by Havel et al [19], wild fires also cause changes in hydrologic response. Tillage and overgrazing affects soil properties and damages soil hydrological properties [16].…”

Intraseasonal Dynamics of River Discharge and Burned Forest Areas in Siberia

“…This is caused by an increase of the interflow in the burned area. Due to an absent transpiration without vegetation cover, more water can infiltrate and contribute to the total runoff [17,18]. Fire can impact the groundwater discharge to surface water features by changing both the supply of water (via an altered recharge) and the transmissivity of the subsurface (via an altered active layer thickness).…”

“…A number of models are available for postfire runoff forecasting in different natural conditions [18][19][20]. According to Springer et al, 2015 [19], in the burned region the runoff generation is slightly increased when compared to the unburned area.…”