Postwildfire hydrological response in an El Niño–Southern Oscillation–dominated environment

Abstract

The rainfall‐runoff events following five fires that occurred within a 40‐year period in eucalypt forests of the Nattai catchment, southeastern Australia, were investigated to quantify the postwildfire hydrological response and to provide context for lower than expected erosion and sediment transport rates measured after wildfires in 2001. Daily rainfall and hourly instantaneous discharge records were used to examine rainfall‐runoff events in two gauged subcatchments (>100 km2) for up to 3 years after fire and compared with nonfire periods. Radar imagery, available from 2001, was used to determine the intensity and duration of rainfall events. Wildfires in the study catchment appear to have no detectable impact on surface runoff at the large catchment scale, regardless of fire severity, extent or time after fire. Instead, the magnitude of postfire runoff is related to the characteristics of rainfall after fire. Rainfall is highly variable in terms of annual totals and the number, size, and type of events. Rainfall events that cause substantial surface runoff are characterized by moderate‐high intensity falls lasting one or more days (≥1 year average recurrence interval). These are triggered by synoptic‐scale weather patterns, which do not reliably occur in the postfire window and are independent of broad‐scale climate dominated by the El Niño–Southern Oscillation (ENSO). This study highlights the importance of considering the characteristics of rainfall, as well as local factors, in interpreting the postfire hydrological response.

Deriving hillslope sediment budgets in wildfire-affected forests using fallout radionuclide tracers

“…The 2001/2002 fires were followed by intermittent rainstorms from late January to April 2002 (prior to the commencement of this study in May 2002) with a rainfall maximum of 63 mm in one event during early February and up to 13 days when rainfall exceeded 10 mm. These events triggered notable overland flow events delivering large quantities of eroded ash, charcoal, organic matter and mineral matter to the stream channels prompting a comprehensive research programme into the hydrogeomorphological consequences of wildfire Shakesby et al, 2003;Doerr et al, 2004;Wallbrink et al, 2005;Blake et al, 2006a,b;Doerr et al, 2006;Blake et al, 2007;Shakesby et al, 2007;Tomkins et al, 2007Tomkins et al, , 2008.…”

“…Comparison with the 137 Cs-derived annual average rates indicates that ant bioturbation is critical for sediment generation after fire (cf. Dragovich and Morris, 2002;Shakesby et al, 2007;Tomkins et al, 2007Tomkins et al, , 2008.…”

Evidence of debris flow occurrence after wildfire in upland catchments of south-east Australia

“…A large majority of the bedrock is of Palaeozoic origin and consists of marine sedimentary rocks (mudstone, shales and sandstone) which in the eastern part of the state have been formed into a belt of metamorphic rocks (schist and gneisses). There is a distinct region of fluvial sedimentary rocks in the (Doerr et al, 2004;Tomkins et al, 2007Tomkins et al, , 2008Blake et al, 2009) Victoria/New South Wales, Jan-Feb 2003 Alpine Fires…”

“…Earlier post-fire erosion research from the region (Brown, 1972;Leitch et al, 1984;Chessman, 1986;Prosser and Williams, 1998) combined with these studies from recently burned areas (Lane et al, 2006;Sheridan et al, 2007a;Smith and Dragovich, 2008;Tomkins et al, 2008;Blake et al, 2009) show clearly that the hydro-geomorphic response of burned upland regions in south-east Australia is highly variable and dependent on a range of factors including i) the fire severity, ii) the timing and properties of post-fire rainfall events, as well as iii) the inherent geomorphic and hydrological characteristics of fire affected catchments. It is noteworthy that much of the research from the region has focused on study sites in gauged catchments (Brown, 1972;Lane et al, 2006;White et al, 2006;Tomkins et al, 2008) where catchment monitoring has been coupled with experiments and process based research (Doerr et al, 2006;Sheridan et al, 2007b;Blake et al, 2009) to provide valuable insights into the processes and controls that influence the post-fire erosion responses in different systems within the region. However, the limitation in conducting research in a fixed and predetermined geographic setting is the low likelihood of capturing data on high magnitude or extreme events.…”

“…The increase in fire activity instigated several field based research projects aimed at quantifying the hydrological effects of fire and the associated impacts on erosion processes and water quality (e.g. Lane et al, 2006;Tomkins et al, 2008). Earlier post-fire erosion research from the region (Brown, 1972;Leitch et al, 1984;Chessman, 1986;Prosser and Williams, 1998) combined with these studies from recently burned areas (Lane et al, 2006;Sheridan et al, 2007a;Smith and Dragovich, 2008;Tomkins et al, 2008;Blake et al, 2009) show clearly that the hydro-geomorphic response of burned upland regions in south-east Australia is highly variable and dependent on a range of factors including i) the fire severity, ii) the timing and properties of post-fire rainfall events, as well as iii) the inherent geomorphic and hydrological characteristics of fire affected catchments.…”