Snowpack Monitoring on the Navajo Nation

Abstract:

The Navajo Nation (N.N.) is the largest sovereign tribal nation by land area in the U.S., about the size of West Virginia. Located in the four corners region of the southwest, the N.N. is largely agrarian and dependent on local water resources. Snowmelt is a crucial component for water availability for recreation, agriculture, and livestock management. Understanding snowpack variability and the implications to water resources in the region are particularly important as the N.N. has been experiencing pervasive and extended droughts in recent years. However, on the N.N., ground-based snow data are limited in space and time. There are currently eight in situ snow course locations, including two that are co-located with snow telemetry (SNOTEL) sites. Snow remote sensing products can help increase the spatial, temporal, and historical length of the snowpack record on the N.N. to better understand trends and variability. In this study, we compared SNOTEL snow water equivalent (SWE) from 2010–2020 Water Years (WYs) to estimated accumulated snowfall from the Parameter-elevation Regressions on Independent Slopes Model (PRISM) and SNow Data Assimilation System (SNODAS) SWE to determine which remote sensing products best characterize N.N. snowpack. These products were then used to evaluate snowpack trends in high elevation regions around the Nation. SNODAS reproduced more than 90% of the variance in SWE at both SNOTEL stations. PRISM estimated accumulated snowfall reproduced at least 70% of the variance of SNOTEL SWE. No significant trend was detected in PRISM estimated accumulated snowfall for the Chuska Mountains, where most snow in the N.N. accumulates. However, from 1982–2020 WY, the number of freezing days decreased at a rate of 0.8 days per WY (p-value < 0.0001). Since SNOTEL maximum winter SWE and number of freezing days each WY were positively correlated (r = 0.7, p-value = 0.02) at both stations, this trend of decreasing freezing days could affect future snowpack accumulation in the Chuska Mountains. Given the ability for remote sensing data to accurately characterize snowpack trends and variability, these datasets provide a viable tool for use by the N.N. Department of Water Resources for future strategic planning.