The Las Conchas record continues after the flames. It links a post-fire hazard assessment with later debris flows and measurements of sediment moving through a river system. That sequence makes it possible to ask whether an early model identified vulnerable tributaries—and what happened downstream afterwards.
The fire and the later storms
Las Conchas began on 26 June 2011 in New Mexico’s Jemez Mountains, according to USGS. A subsequent USGS assessment estimated debris-flow hazards under a specified rainfall scenario. A 2024 study then examined the consequences of intense precipitation in July and September 2013 in the Rito de los Frijoles watershed. These are separate dates: fire, storm response and research publication. [1,2,3]
What the original probability means
The preliminary assessment evaluated a design storm delivering 28 millimetres in 30 minutes, identified as a ten-year recurrence event. Under that scenario, estimated debris-flow probabilities exceeded 80% in 67% of the modelled basins. The percentages describe a conditional model result, not a claim that debris flows happened in all those basins during 2011. [2]
Tecnobosque analysis: a hazard probability needs its rainfall condition attached. Removing the storm specification turns a useful assessment into an apparently timeless prediction. A recurrence interval also describes a statistical frequency, not an appointment that weather keeps once every ten years.
What later measurements added
Friedman and colleagues compared lidar elevation models from 2010 and 2016. Their 2024 paper reports debris flows in seven of nine sub-basins with assessed hazard above 60% for a 25-year rainfall event, and none in 21 sub-basins below that threshold. This comparison uses its own storm scenario and basin set; it is not a direct repetition of the ten-year-storm percentage above. [3]
The paper reports an average bed-elevation increase of 0.29 metres along a 22-kilometre trunk stream, with local changes varying substantially. Sediment entered at tributary junctions and was redistributed during subsequent floods. [3]
Why an average cannot describe every crossing
A mean rise along a long channel is not the amount of sediment at a particular bridge. Deposition in one reach and erosion in another can coexist with the same overall mean. For an infrastructure assessment, the location of tributary inputs and changes in channel gradient matter as much as the aggregate volume.
The lidar dates also bracket several years. An elevation difference between surveys measures net change over that interval. Assigning every centimetre of that difference to one storm requires additional timing evidence. The publication’s flood reconstruction adds context, but the survey interval should remain visible.
What makes this evidence chain useful
The strength of the case is the opportunity to compare a forecast with later observations and then investigate downstream redistribution. The limits are equally concrete: different storm scenarios, different basin populations and measurements taken at different times cannot be mixed casually.
For comparison with the Station Fire, focus on the distinction between modelled hazard and instrumented or surveyed response. For comparison with Jasper, note that physical watershed change is a separate recovery dimension from rebuilding properties. Neither endpoint alone describes a community’s full post-fire exposure.
FireDNA: conditional hazard model · lidar change detection · sediment redistribution.
Primary sources and technical records
- USGS New Mexico wildfire science: incident context
- USGS OFR 2011-1308: preliminary debris-flow hazard assessment
- Friedman et al. (2024): sediment redistribution; DOI 10.1002/esp.5964
Related case studies
- Hermits Peak / Calf Canyon 2022 — Separating a prescribed-fire escape from a holdover pile burn, then following the post-fire monitoring record.
- Station Fire 2009 — Why post-fire hazard depends on rainfall assumptions, sediment storage and downstream exposure.
- Browse the complete Fire Archive