Understanding the main drivers of hydrological drought in a large alpine watershed

Abstract ID: 3.11246 | Accepted as Talk | Talk | TBA | TBA

Andrea Galletti (1)
Susen Shrestha (2), Stefano Terzi (1), Mariapina Castelli (1), Giacomo Bertoldi (1)
(1) Eurac Research, Viale Druso 1, 38100, Bolzano, Italy
(2) University of Padova, Via 8 Febbraio 2, 35122, Padova, Italy

Categories: Water Resources
Keywords: drought, drivers, classification

Categories: Water Resources
Keywords: drought, drivers, classification

Alpine regions are increasingly vulnerable to droughts due to the compounding effects of extreme climate events and conflicting water uses. This study focuses on the Upper Adige catchment, where shifts in its traditionally snow-driven hydrological regime are intensifying, calling for systematic adaptation to meet diverse demands across agriculture, ecosystems, and hydropower. We investigated the leading causes of hydrological drought in this area analyzing 27 drought events related to the 1997-2022 time window. We apply the conceptual hydrological model ICHYMOD to assess key drought formation mechanisms in the region. The model is initially validated against observed streamflow time series and demonstrates reliable performance in capturing both dry and wet day patterns and in identifying severe drought events, with accuracy exceeding 75% across several validation sites. The analysis then focuses on a model-based evaluation of hydrological drought formation with reference to the entire Upper Adige basin, assessing how drought propagates through the hydrological cycle and identifying recurrent patterns. A tree-based classification framework aimed at classifying the droughts according to their driving mechanism is developed, deriving threshold and classification criteria informed by expert knowledge of the region. Sensitivity analysis confirmed the chosen classification thresholds. The observed events are automatically classified into six categories, closely mirroring the outcome of visual classification, affirming the robustness of the approach and its alignment with domain expertise. Droughts originating from two or more leading mechanisms are classified as composite. Our results highlight that the longest droughts are typically driven by either early snowmelt, which depletes summer water reserves and triggers an early start of the vegetative season, or by precipitation deficits heading into winter, which lead to prolonged recessions of water resources. These drought categories also record the highest deficits in terms of streamflow volume. The lowest streamflows typically occur in spring, driven by either rainfall deficits or delayed snowmelt at the end of the winter recession. Temperature emerges as a key driver with contrasting effects: while high temperatures accelerate snowmelt and exacerbate summer droughts, excessively low temperatures prolong winter recessions, intensifying spring water conflicts when demands are most critical.

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