Avanzi et al. (2026) Impacts of Mediterranean snow droughts on mountain socio-ecohydrology

Identification

• Journal: Hydrology and earth system sciences
• Year: 2026
• Date: 2026-09-14
• Authors: Francesco Avanzi, Stefano Terzi, Mariapina Castelli, Francesca Munerol, Margherita Andreaggi, Marta Galvagno, Andrea Galletti, Tessa Maurer, Christian Massari, Grace A. Carlson, Manuela Girotto, Giacomo Bertoldi, Edoardo Cremonese, Simone Gabellani, Umberto Morra di Cella, Marco Altamura, Lauro Rossi, Luca Ferraris
• DOI: 10.5194/hess-30-5769-2026

Research Groups

• CIMA Research Foundation, Savona, Italy
• Eurac Research, Bolzano, Italy
• Climate Change Unit, Environmental Protection Agency of Aosta Valley, Saint-Christophe, Italy
• Blue Forest, Sacramento, CA, USA
• National Research Council (CNR), Research Institute for Geo-Hydrological Protection, Perugia, Italy
• Department of Environmental Science, Policy, and Management, University of California, Berkeley, Berkeley, CA, USA
• Dipartimento di informatica, bioingegneria, robotica e ingegneria dei sistemi – DIBRIS, Università di Genova, Genova, Italy

Short Summary

This study comprehensively investigates the multi-sectoral socio-ecohydrological impacts of snow droughts in 38 Italian mountain catchments over 13 years, revealing that warm-dry snow droughts lead to shortened snow seasons, reduced summer runoff, increased vegetation Gross Primary Production at higher elevations, and widespread water-supply restrictions affecting both lowlands and high-elevation mountain communities.

Objective

• To characterize the signature of snow droughts on snow-cover duration and runoff efficiency.
• To determine whether snow droughts lead to an increase or decrease in Gross Primary Production (GPP) and its spatio-temporal patterns.
• To identify the temporal characteristics of water-supply and societal impacts of snow droughts across an elevation gradient.

Study Configuration

• Spatial Scale: 38 headwater catchments across Italy (Alps and Apennines). Median catchment size 430 square kilometers, median elevation 1830 meters above sea level. Analysis performed across 500-meter elevation bands from 500 to 3500 meters above sea level.
• Temporal Scale: 13 water years (1 September 2010 – 31 August 2023). Societal impact data primarily focused on 2022–2023.

Methodology and Data

• Models used:
  • IT-SNOW reanalysis (for Snow Water Equivalent, SWE)
  • Penman–Monteith–Leuning Evapotranspiration product, PML_V2 (process-based water-carbon coupled model for Gross Primary Production, GPP)
• Data sources:
  • Hydro-meteorology:
    • Streamflow: In-situ gauges from Italian Regional Administrations and Autonomous Provinces, and an Alpine hydrological dataset (daily, point).
    • Snow Water Equivalent (SWE): IT-SNOW reanalysis (daily, 500 meter spatial resolution).
    • Precipitation and Temperature: BIGBANG dataset (interpolation of 2000+ in-situ stations, monthly, ~1 kilometer spatial resolution).
  • Terrestrial-ecosystem impacts:
    • Gross Primary Production (GPP): Remote sensing (PML_V2, 8-day interval, 500 meter spatial resolution).
    • Greening date: Remote sensing (MODIS MCD12Q2v061, daily, 500 meter spatial resolution).
    • Flux-tower data: In-situ (Integrated Carbon Observation System (ICOS) Aosta Valley, IT-TrF forest, IT-Tor grassland, daily, point).
  • Societal impacts:
    • Emergency water restrictions: Regulatory records compiled via web scraping and direct consultation of national to local regulations (daily, point).
    • Mountain hut survey: Online survey among 113 hut managers (point).

Main Results

• Snow Drought Characteristics: 152 snow droughts were identified across the 38 catchments. The majority (53%) were classified as warm-dry (low precipitation and higher-than-usual temperatures), followed by warm-wet (22%), cold-dry (17%), and cold-wet (8%).
• Cryosphere and Hydrology:
  • Snow droughts led to a statistically significant decline in snow-cover duration across all elevations, shortening the snow season by a median of 8 to 31 days, with the largest reductions at 1000–2000 meters above sea level.
  • An increase in snow ephemerality (more intra-seasonal melt-out events) was observed above 1000 meters above sea level, peaking at 1500–3000 meters above sea level (up to +0.6 times more melt-out events).
  • Summer runoff decreased by a median of 50% across all catchments following snow droughts, despite no significant change in summer precipitation, but with a statistically significant increase in summer temperature.
  • The number of annual low-flow days increased by a median of 33 days per year, and the annual runoff ratio declined by a median of 0.06.
• Terrestrial Ecosystems:
  • Growing-season Gross Primary Production (GPP) after a snow drought was up to 10% higher than after non-snow-drought winters, particularly above 1500 meters above sea level.
  • Snow droughts resulted in an earlier greening date at all elevations (1–3 days below 2500 meters above sea level, 6–8 days above 2500 meters above sea level), associated with increased spring average temperature.
  • Ground-based flux-tower data confirmed an earlier rise in GPP. Grassland sites showed a late-season GPP drop due to soil moisture depletion, while forest sites maintained GPP, leading to higher cumulative GPP.
• Societal Impacts:
  • Emergency water-use restrictions affected approximately 16% (1291 out of ~7900) of Italian municipalities during the 2022 and 2023 droughts, with the highest density in the foothill regions of the Alps and Apennines.
  • Restrictions were issued across all elevations, with a peak between May and July at higher elevations.
  • Approximately 70% of mountain hut managers (average elevation 1800–2200 meters above sea level) reported water-supply impacts, and 28% reported earlier closing dates due to water scarcity.

Contributions

• Provides the first comprehensive, multi-sectoral (cryosphere, hydrology, ecology, society) and multi-elevation assessment of snow drought impacts in Mediterranean regions, using Italy as a case study.
• Identifies the prevalence of "warm-dry" snow droughts as the dominant type, highlighting a critical climate-change-driven scenario for mountain systems.
• Quantifies the increase in snow ephemerality (intra-seasonal melt-out events) during snow droughts, particularly at intermediate elevations, addressing a key knowledge gap.
• Reveals a counter-intuitive increase in vegetation Gross Primary Production (up to 10%) and earlier greening dates at higher elevations after snow droughts, linking it to a longer growing season in energy-limited environments.
• Demonstrates that societal water-supply impacts, including restrictions and mountain hut closures, occur across all elevations, with a surprising escalation in upstream (mountain) areas due to vulnerable infrastructure and policy gaps, challenging the traditional view of downstream-only impact propagation.
• Emphasizes the urgent need for a systemic, rather than sectoral, understanding and adaptive management of snow drought risks in a warming climate.

Funding

• NextGenerationEU (grant no. PE0000005)
• Interreg (grant no. ASP0500403)
• Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung (grant no. 200021L 205190)
• Italian Civil Protection Department

Citation

@article{Avanzi2026Impacts,
  author = {Avanzi, Francesco and Terzi, Stefano and Castelli, Mariapina and Munerol, Francesca and Andreaggi, Margherita and Galvagno, Marta and Galletti, Andrea and Maurer, Tessa and Massari, Christian and Carlson, Grace A. and Girotto, Manuela and Bertoldi, Giacomo and Cremonese, Edoardo and Gabellani, Simone and Cella, Umberto Morra di and Altamura, Marco and Rossi, Lauro and Ferraris, Luca},
  title = {Impacts of Mediterranean snow droughts on mountain socio-ecohydrology},
  journal = {Hydrology and earth system sciences},
  year = {2026},
  doi = {10.5194/hess-30-5769-2026},
  url = {https://doi.org/10.5194/hess-30-5769-2026}
}