6.1.8 Debris Flows and Human Detritus: Wildfires’ Hydrological Footprint

“An old, grim joke about California says that the state has only three seasons: summer, fire, and mudslides”. Rogers, 2017.

True to wildfire’s synergetic form, its relationship with regional hydrology is non- linear, instead extending across space and time both within and beyond the boundary of its burn scar. As discussed earlier, while fast-moving low-severity wildfires leave soils unheated and overstories in-tact, high severity wildfires are frequently stand- replacing events, therein have capacity to significantly disrupt soil hydrology, thus soil’s structural integrity. In the aftermath of a high-severity fire, regional flooding and runoff can increase for a period of several years, with post-fire debris flows commonplace in the first two, and typically triggered by the onset of the storm season (USGS, 2017). Such is the instability of soils in some post-fire watersheds that a mere 7m or more rainfall in 30 minutes can cause debris flows (Ibid). Often occurring with little or no warning, post-fire debris flows can pose significant threat to human life and property, as is evidenced by the events as followed the Thomas Fire, when “rivers of mud and debris” destroyed many lives and homes in their path (Queally et al, 2018) [Fig. 62]. If the wildfire was the jab, the debris flow was the cross, in a one-two punch hazard combination, as expressed in such headlines as, “Fires and mudslides have some rethinking the Californian dream” (Dobuzinskis, 2018).

However, in fire-prone coastal regions, post-fire debris, and other particulate flows impact not merely on terrestrial biotic and abiotic systems, but marine environments also. While the effects are yet to be analysed, satellite footage from the Thomas Fire evidenced significant ash fallout reached the Pacific Ocean (Schmaltz, 2017). Previous studies of the impacts of nutrient-rich wildfire runoffs found that algae blooms may result, and on such scale as could trigger ecological regime shifts (Morrison and Kolden, 2014). As highlighted by the ecologist Daniel Botkin (2012), in and of itself, change, including variations in species composition, populations, and distributions, is fundamental to ecosystem functioning. Within living memory, the wildfire events of late appear ‘extreme’. But, when compared to wildfires within geological memory, they are yet a magnitude smaller than has occurred in past epochs. Hence, though not necessarily conserving the particular ecosystem configurations of present, more likely than not, in the words of one of Michael Crichton’s most famous characters [Dr. Ian Malcolm] marine life will find “a way” (1990) to adapt to the influx of nutrients. However, as with other forms of anthropogenic pollution [i.e. plastic debris], the degree to which oceanic species have the capacity to coexist with the chemical remnants of burnt out vehicles and homes is yet to be quantified (Westman, 2017). In the interim, given the qualitative difference between ash produced at relatively low and high temperature [the former predominantly composed of organic carbon, the latter vice versa] suggests that, as in terrestrial ecosystems, the runoff of low, mixed, and high severity fire regimes will produce notably different impacts. Thus, whereupon evaluating the ecological impacts of fires within the wildland urban interface one needs think beyond it.

>Continue to Chapter 6.1.9.1 here.

The thesis is also available in PDF format, downloadable in several parts on Academia and Researchgate.

Note that figures have been removed from the digital version hosted on this site, but are included in the PDFs available at the links above.

Citation: Sterry, M. L., (2018) Panarchistic Architecture: Building Wildland-Urban Interface Resilience to Wildfire through Design Thinking, Practice and Building Codes Modelled on Ecological Systems Theory. PhD Thesis, Advanced Virtual and Technological Architecture Research [AVATAR] group, University of Greenwich, London.