New Mexico Geological Society Annual Spring Meeting — Abstracts

Forest fires are well known to impact the quality of water in a watershed from hillside erosion and fire sedimentation as well as the quantity of water entering the system from decreased soil infiltration, lessened vegetation interception, and increased catchment evapotranspiration. The Gallinas Watershed in northern New Mexico was impacted by the 2022 Hermits Peak/Calf Canyon (HP/CC) Fire, the largest wildfire in New Mexico’s history (>340,000 acres). Approximately 115,542 acres burned in the Headwaters Gallinas River Watershed, 21% of which were classified by the USFS Burned Area Emergency Response team as high burn severity. While much research focuses on the increased flooding from monsoonal rains after a forest fire, little data exists about wildfire impact on snowmelt runoff. We are monitoring the Gallinas River’s discharge during the spring runoff (March through May) to test what if any impact the 2022 HP/CC forest fire has on streamflow. As of March 25, 2024, the snowpack depth at the NRCS Wesner Springs snow monitoring station at the Gallinas River’s source (Elk Mountain; 11,151 feet) stands at 43.0 in. and snow water equivalent is 13.3 in., which are both higher than the 30-year median by 116% and 106% respectively. The above-average snowpack raises concerns for increased snowmelt in the watersheds, with heightened concern for earlier onset and higher levels of peak flows due to post-fire watershed conditions. We have been monitoring in near real-time the SWE, air temperature, and soil moisture at Wesner Springs and comparing these data to both historic and 2024 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, NM (USGS 08380500) show generally broad and diffuse trends with step-wise increases in discharge from March to May from snow melt in contrast to the narrow, sharp, and marked increases in discharge from June to August from monsoon rains. The Spring 2023 Gallinas River hydrograph had a similar pattern to historic trends (step-wise increase in discharge with peak runoff (214 ft³/sec) in mid-April. The Spring 2024 Gallinas River hydrograph (as of March 25^th) shows a flashy response with the highest runoff to date of 32.9 ft³/sec. The NRCS National Water and Climate Center has calculated a forecast volume (50% exceedance probability) of 101% of the 30-year median at Gallinas Creek near Montezuma. Historically, peak discharge on the Gallinas occurs around May 15^th based on the 96-year record, but has been occurring earlier during the millennium drought. This year, with the above average snowpack, post-fire conditions, and departure of the hydrograph from historic trends, monitoring in near real-time is imperative to forecast flood stages, manage fire sedimentation, and protect water supplies.