Spatial and Temporal Variability of Snow in the Andes using MODIS Snow Product 2000-2024

Freddy Saavedra^1,2,3*Ana Hernández-Duarte^1,2,3Alexis Caro^4,5Antoine Rabatel⁶Steven Fassnacht^2,7Thomas CONDOM⁶Stephanie Kamp⁸Mariano Masiokas⁹Yael Aguirre¹⁰Daniela González¹¹Valentina Contreras^2,3Javier Medina^2,3Pablo Arancibia^2,3

• ¹Universidad de Playa Ancha, Valparaíso, Chile
• ²Environmental Remote Sensing Laboratory, University of Playa Ancha, Valparaíso, Chile
• ³HUB Ambiental, Universidad de Playa Ancha, Valparaíso, Chile
• ⁴Departamento de Ingeniería de Obra Civil, Facultad de Ingeniería y Ciencias, Universidad de La Frontera, Temuco, Chile
• ⁵UMR5001 Institut des Géosciences de l'Environnement (IGE), St Martin D Heres, Rhône-Alpes, France
• ⁶Institut des Géosciences de l'Environnement (IGE, UMR 5001), Université Grenoble Alpes, Saint Martin d'Hères, Auvergne-Rhone-Alpes, France
• ⁷Colorado State University, Fort Collins, Colorado, United States
• ⁸Department of Ecosystem Science and Sustainability, Warner College of Natural Resources, Colorado State University, Fort Collins, Colorado, United States
• ⁹CONICET Argentine Institute of Nivology, Glaciology and Environmental Sciences (IANIGLA), Mendoza, Mendoza, Argentina
• ¹⁰Hydrographic and Oceanographic Service of the Chilean Navy, Valparaíso, Chile
• ¹¹Servicio Aerofotogramétrico, Fuerza Aérea de Chile, Santiago, Chile

Snow is a critical component of the Andean hydrological system, sustaining water supply for drinking, irrigation, hydropower, and industry. Persistent cloud cover and limited in situ observations have hindered long-term assessments of snow dynamics across the world's longest mountain range. Here, we present a continent-scale analysis of snow persistence (SP) and snowline elevation from 2000 to 2024 using daily MODIS Terra–Aqua products enhanced with advanced temporal and spatial cloud-reduction algorithms. Cloud persistence was reduced overall from 49% to 29%, substantially increasing the usable observational record for snow detection but cloud-related limitations persist in tropical and southern Patagonia regions. Our results reveal that snow responses are strongly heterogeneous along the mountain chain. Ther is a marked and spatially coherent decline in SP between 29°S and 36°S, where approximately 78,000 km² of snow-covered area have been lost over the past 25 years. In this same region, the snowline rose by 5–15 m/yr, reaching cumulative increases of up to 500 m. At the watershed scale, only basins the Central Andes (29 °S – 36 °S) exhibit statistically significant SP declines and rising snowlines, while tropical watersheds show minimal snow presence and southern Patagonia displays mixed patterns influenced partially by persistent cloud cover. The accelerating loss of seasonal snow in the central Andes has profound implications for water security in regions where snowmelt is a dominant hydrological input. Our results underscore the need for higher-resolution multispectral and radar observations, expanded ground-based monitoring, and integrative modeling approaches to quantify snow water equivalent and anticipate future changes. Collectively, this study provides the most comprehensive assessment to date of Andean snow dynamics and highlights the central Andes as a hotspot of cryospheric sensitivity to ongoing climate change.