Using NASA Earth Observations to Monitor Snow Cover Extent for Water
Resource Management on the Navajo Nation
Abstract
The southwestern U.S. has been experiencing prolonged drought conditions
contributing to declines in snowpack and surface water supply. On the
Navajo Nation (NN), the largest U.S. federally recognized sovereign
tribal nation in land area, snowpack is an essential reservoir for
surface water storage and aquifer recharge, but has not been extensively
monitored. Within the NN, only two high elevation regions, Chuska
Mountains and Defiance Plateau, have in-situ snow monitoring at eight
sites (consisting of two SNOTEL stations and eight snow courses). With
climate change contributing to long-term temperature increases, patterns
of snowfall and snowmelt are changing and NN leaders are recognizing the
need for more detailed and reliable monitoring systems. This study
explored how NASA Earth Observations can be used to provide more
frequent, high-resolution tracking of snow cover extent on the NN, and
how those data can offer actionable insights for local water managers.
The Normalized Difference Snow Index (NDSI), as derived from NASA MODIS
products, was used to create daily cloud/gap-free images of Snow Covered
Area (SCA) during the winter months (November – April) from 2002 to
2018. Aggregated weekly and monthly means were then constructed to study
spatial and temporal anomalies in SCA. These data were compared with the
available ground-based measurements of snow water equivalent (SWE).
Results indicate that SCA anomalies can serve as a proxy for monitoring
snowpack variability across all high-elevation areas of the NN. SCA
anomalies also suggest that the NN snowpack is exhibiting increased
variability during peak winter months, along with declines in the spring
months, consistent with broader regional climate trends. This study aids
in the establishment of remotely sensed snow monitoring on the NN.
Further analyses would be improved through the use of additional snow
products, such as the MODIS Snow Covered-Area and Grain size retrieval
algorithm (MODSCAG) to estimate fractional snow cover and snow grain
size, and NASA’s Airborne Snow Observatory (ASO) to estimate snow albedo
and SWE.