Preprints
https://doi.org/10.5194/nhess-2024-6
https://doi.org/10.5194/nhess-2024-6
18 Jan 2024
 | 18 Jan 2024
Status: this preprint is currently under review for the journal NHESS.

Compound droughts under climate change in Switzerland

Christoph Nathanael von Matt, Regula Mülchi, Lukas Gudmundsson, and Olivia Martius

Abstract. The co-occurrence of meteorological, agricultural, and hydrological droughts (multivariate compound droughts) in Switzerland during growing season is problematic due to limitations in water abstractions from rivers during low flow periods, while at the same time the need for irrigation is high. We analyse compound droughts for 52 catchments in Switzerland during the extended summer season (May–Oct) using the transient climate and hydrological scenarios for Switzerland (CH2018 and Hydro-CH2018) for both a scenario with mitigation (RCP2.6, 8 model chains) and without mitigation (RCP8.5, 20 model chains). In the RCP8.5 scenario the number of compound drought days is projected to significantly increase by mid-century across all greater regions of Switzerland. The increased frequency is mainly a result of more frequent events (significant) rather than longer event durations (non-significant). Models generally agree on the sign of change. By 2085, compound drought events are projected to occur in median once per catchment per extended summer season north of the Alps and every 1–2 years south of the Alps. Further, the increases in compound drought days mainly occur between May–Oct leading to a shift into the main agricultural production season and a more pronounced seasonality with highest occurrence probabilities between mid-July and the begin of October. Coupled to the increase in days and events, significantly more catchments are projected to be affected by compound droughts at the same time. In the RCP2.6 (mitigation) scenario, the increase in the number of compound drought days and events is not significant by the end of the 21st century. In comparison with RCP8.5, the number of compound drought days are reduced by 50–55 % north of the Alps and up to 75 % south of the Alps by the end of the century. This emphasizes the need for coordinated adaptation in combination with mitigation measures taken at early stage.

Christoph Nathanael von Matt, Regula Mülchi, Lukas Gudmundsson, and Olivia Martius

Status: open (until 08 Mar 2024)

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Christoph Nathanael von Matt, Regula Mülchi, Lukas Gudmundsson, and Olivia Martius
Christoph Nathanael von Matt, Regula Mülchi, Lukas Gudmundsson, and Olivia Martius

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Short summary
The simultaneous occurrence of meteorological (precipitation), agricultural (soil moisture) and hydrological (streamflow) drought can lead to augmented impacts. By analysing drought indices derived from newest climate scenarios for Switzerland (CH2018, Hydro-CH2018), we show that with climate change the concurrence of all drought types will increase in all investigated regions of Switzerland. Our results highlight the benefits and need of both mitigation and adaptation measures at early stages.
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