New Mexico Geological Society Annual Spring Meeting — Abstracts

The 2022 Hermits Peak/Calf Canyon (HP/CC) Fire, the largest wildfire in New Mexico’s history (>340,000 acres), impacted the Gallinas River – the City of Las Vegas’ drinking water supply. Approximately 115,542 acres burned in the Gallinas River headwaters with 21% classified as high burn severity. While much data exists about increased flooding from monsoonal rains after a forest fire, little data exists about the hydrologic impacts of a forest fire during spring runoff. We have been monitoring in near real-time snow water equivalent (SWE), air temperature, and soil moisture at the Gallinas River’s source (Wesner Springs; 11,151 feet) and comparing these data to both historic and current Gallinas River discharge data with emphasis on the period during the spring snowmelt (March through May) to test what if any impact the 2022 HP/CC forest fire is having on hydrologic conditions. Historically, the hydrographs for Gallinas Creek near Montezuma (USGS 08380500) generally show broad and diffuse trends with stepped discharge increases from March through May from snowpack melt in contrast to narrow, sharp, and punctuated increases in discharge from June through August from monsoon rains. The spring 2023 and 2024 Gallinas River hydrographs showed similar patterns to pre-fire trends. Peak runoffs (2023: 214 ft³/sec and 2024: 73.4 ft³/sec) showed the same order of magnitudes as years with similar snow water equivalents (SWE). The spring 2025 Gallinas River hydrograph pattern departs from historic trends. Rather than a stepwise increase in discharge, the hydrograph shows relatively low, steady, near baseflow values. Snow depth peaked on November 8, 2024 at 30 inches and has been steadily declining ever since. As of April 4, the snowpack depth and SWE are at 1.0 and 0.2 inches, respectively. The 2025 snow drought conditions make hydrographic comparison to pre-fire years impossible. Monitoring post-fire spring hydrograph patterns in near real-time remains imperative to forecast flood stages, manage fire sedimentation, and protect water supplies during average- to above-average snowpack years and to forecast drought stages, conserve water supplies, and support adaptation decision-making during below-average snowpack years.