Abstract ID: 3.12050 | Accepted as Talk | Requested as: Talk | TBA | TBA

We assess the impact of two recent meteorological summer droughts ‒ 2018 and 2022 ‒ on the hydrology of Swiss catchments. Both summers featured precipitation deficits of ~30% and temperature anomalies of +1.5°C, relative to the 1994-2023 average. To analyse these events, we perform a detailed numerical simulation of Switzerland’s hydrological cycle from 2016 to 2023 using the mechanistic eco-hydrological model Tethys-Chloris (T&C). T&C calculates energy and mass fluxes using physics-based representations of hydrological, biospheric and cryospheric processes at 250 m spatial resolution and hourly time steps, providing spatially-distributed estimates of runoff, evapotranspiration, snowmelt, ice melt, vegetation productivity, and others. T&C is forced with observed meteorological hourly data, and uses up-to-date information on land cover, soil and glacier properties. Model results are consistent with observations of streamflow, snow variables, glacier mass balance, LAI, soil moisture, and fluxes of CO2, water and energy.

Although both summer droughts led to widespread runoff deficits, model results show that the relatively wet winter of 2018 mitigated summer drought impacts compared to 2022, which followed a snow-poor winter. Above-average snow accumulation in winter 2018 resulted in a +100 mm w.e. spring snowmelt anomaly across the Alpine region (relative to the 2016-2023 average), whereas spring 2022 had a −50 mm w.e. anomaly. The 2022 winter snow deficit triggered >50 mm w.e. of excess glacier meltwater in early summer, whereas only a weak positive anomaly was found in late summer 2018. Soil moisture deficits in 2018 were mostly limited to the Central Plateau, reaching values down to −35%, whereas in 2022 anomalies were more widespread ranging from −15% to −35%. Summer evapotranspiration remained near-average in 2018 but showed a +50 mm anomaly in 2022, especially above 1000 m a.s.l. We show that detailed representation of the hydrological cycle in T&C enables a comprehensive understanding of the widespread effects of a summer drought over Switzerland, including the complex and interconnected responses of rivers, vegetation and the cryosphere.