Stucchi et al. (2026) Assessing Meteorological (1950–2022) and Hydrological (1911–2022) Trends in the Northwestern Alps: Insights from the Upper Po River Basin

Identification

• Journal: Water
• Year: 2026
• Date: 2026-01-30
• Authors: Leonardo Stucchi, Diego Jacopino, Sergio Pisani, Maurizio Maugeri, Daniele Bocchiola
• DOI: 10.3390/w18030348

Research Groups

• Department of Civil and Environmental Engineering, Politecnico di Milano, Italy
• Department of Environmental Science and Policy, University of Milan, Italy

Short Summary

This study investigates transboundary hydro-meteorological trends in the Upper Po River basin, revealing pronounced warming, increased potential evapotranspiration, and a significant decline in summer streamflow, indicating a transition from nival to pluvial hydrological regimes.

Objective

• To investigate transboundary hydro-meteorological trends in the Upper Po River basin, adopting a multi-perspective framework to disentangle the joint evolution of climatic and hydrological drivers.
• To assess the response of flow discharge to climatic drivers within the studied catchment using statistical correlation analysis.

Study Configuration

• Spatial Scale: Upper Po River basin, located in the northwestern Alps, spanning northern Italy (Piedmont, western Lombardy) and southern Switzerland (Valais, Ticino). The total area is 12,665 km², encompassing five major sub-basins (Ticino, Toce, Sesia, Agogna, Terdoppio Novarese).
• Temporal Scale:
  • Meteorological data (precipitation, temperature, evapotranspiration): 1950–2022 (from 25 weather stations, with varying start years).
  • Hydrological data (streamflow): 1911–2022 (from 14 river sections).
  • Gridded dataset for correlation analysis: 1900–2021.

Methodology and Data

• Models used:
  • Mann–Kendall (M-K) test: Non-parametric test for detecting monotonic trends (significance level p-value = 0.05).
  • Theil-Sen estimator: For quantifying the magnitude of trends.
  • Thornthwaite equation: For calculating monthly potential evapotranspiration (PET).
  • Pearson’s correlation coefficient, Spearman’s rank correlation coefficient, and Kendall’s rank correlation coefficient: For assessing correlations between hydro-climatic variables.
• Data sources:
  • Climate data:
    • 25 daily time series of precipitation and temperature (minimum, average, maximum) from stations in Switzerland (MeteoSwiss) and Italy (ARPA Lombardia, ARPA Piemonte).
    • Monthly gridded dataset (30 arc-seconds resolution, approximately 700 m) for 1900–2021, based on an enhanced version of the dataset presented in [28], reconstructed using the anomaly method.
  • Hydrometric data:
    • 14 hydrometric stations providing daily discharge records across five main catchments (Agogna, Sesia, Terdoppio Novarese, Toce, Ticino).
    • Water level records from Lake Maggiore (at Sesto Calende).

Main Results

• Temperature Trends: Pronounced warming observed, particularly in spring maximum temperatures (+0.95 ± 0.40 °C per decade) and at the annual scale (+0.62 ± 0.35 °C per decade for maximum, +0.50 ± 0.26 °C per decade for average, and +0.39 ± 0.27 °C per decade for minimum temperatures). Warming rates have intensified significantly since the 1980s, with maximum temperatures rising faster than minimums.
• Potential Evapotranspiration (PET) Trends: Significant increase of +15.1 ± 9.4 mm per decade.
• Precipitation Trends: Generally lacks significant long-term trends at the annual scale, but a localized negative trend in summer (JAS) was observed in 5 out of 25 stations.
• River Discharge Trends: Significant negative trends in summer (JAS) in 9 out of 14 stations, with no significant annual trend. Weak positive trends were observed in winter (JFM), possibly due to a shift from snowfall to rain.
• Lake Maggiore: No significant trends in water levels or volumes, indicating that reservoir regulation does not significantly alter downstream flow dynamics at the seasonal scale.
• Correlation Analysis: Strong linear relationships between discharge and climatic variables, with annual precipitation correlations reaching up to r = 0.95. Maximum temperatures show primarily negative correlations with discharge. Minimum temperatures exhibit negative correlations in spring and summer, but positive in autumn and winter. Snow dynamics significantly modulate the hydrological response, with the weakest coupling between precipitation and discharge in winter due to snow accumulation.

Contributions

• Provides a comprehensive multi-perspective framework to analyze the joint evolution of climatic and hydrological drivers in the Upper Po River basin, distinguishing it from previous studies that often focused on single variables.
• Quantifies the combined effects of warming and increased evapotranspiration on water availability, particularly the decline in summer streamflow, in a region critical for European agriculture and industry.
• Confirms a structural shift in the hydrological regime of Alpine catchments from nival (snow-dominated) to pluvial (rain-dominated) behaviors, altering the timing of water availability.
• Offers a quantitative basis for developing effective adaptation strategies to address increasingly scarce summer water resources in the region.

Funding

• Project CCHP-ALPS (Prot. 2022CN4RWK, CUP. D53D23004630006.)—Climate Change and HydroPower in the Alps—funded by the Italian Research Program PRIN 2022, which is funded by the EU (NextGenerationEU funds).
• ANVCO-ADAPT, 2025–2027 funding agreement from Acqua Novara Verbano Cusio Ossola ANVCO Company.

Citation

@article{Stucchi2026Assessing,
  author = {Stucchi, Leonardo and Jacopino, Diego and Pisani, Sergio and Maugeri, Maurizio and Bocchiola, Daniele},
  title = {Assessing Meteorological (1950–2022) and Hydrological (1911–2022) Trends in the Northwestern Alps: Insights from the Upper Po River Basin},
  journal = {Water},
  year = {2026},
  doi = {10.3390/w18030348},
  url = {https://doi.org/10.3390/w18030348}
}