EMS Annual Meeting Abstracts
Vol. 18, EMS2021-201, 2021, updated on 09 Jan 2024
https://doi.org/10.5194/ems2021-201
EMS Annual Meeting 2021
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

The Swiss Alpine zero degree line: methods, past evolution, sensitivities

Simon C. Scherrer1, Stefanie Gubler1, Kathrin Wehrli1,2, Andreas M. Fischer1, and Sven Kotlarski1
Simon C. Scherrer et al.
  • 1Federal Office of Meteorology and Climatology MeteoSwiss, Climate Division, Zürich-Flughafen, Switzerland (simon.scherrer@meteoswiss.ch)
  • 2Center for Climate Systems Modeling C2SM, ETH Zürich, Switzerland

The near-surface zero degree line (ZDL) is a key isotherm in mountain regions worldwide, but a detailed analysis of methods for the ZDL determination, their properties and applicability in a changing climate is missing. We here test different approaches to determine the near-surface ZDL on a monthly scale in the Swiss Alps. A non-linear profile yields more robust and more realistic ZDLs than a linear profile throughout the year and especially in the winter-half year when frequent inversions disqualify a linear assumption. In the period 1871-2019, the Swiss ZDL has risen significantly in every calendar month: In northern Switzerland, the monthly ZDL increases generally amount to 300-400 m with smaller values in April and September (200-250 m) and a larger value in October (almost 500 m). The largest increases of 600-700 m but also very large uncertainties (±400 m, 95% confidence interval) are found in December and January. The trends have accelerated in the last decades especially in spring and summer. The ZDL has increased by ~160 m per °C warming in the summer-half year and up to 340±45 m/°C in winter months. In southern Switzerland, ZDL trends and temperature scalings are somewhat smaller, especially in winter. Sensitivity analyses using a simple shift of the non-linear temperature profile suggest that the winter ZDL-temperature scalings are at a record high today or will reach it in the near future, and are expected to decrease with a strong future warming. Nevertheless, the cumulative ZDL increase for strong warming is considerably larger in winter than in summer. Based on a few key criteria, we also present best practises to determine the ZDL in mountain regions worldwide. The outlined methods lay a foundation for the analysis of further isotherms and to study the future ZDL evolution based on climate scenario data.

How to cite: Scherrer, S. C., Gubler, S., Wehrli, K., Fischer, A. M., and Kotlarski, S.: The Swiss Alpine zero degree line: methods, past evolution, sensitivities, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-201, https://doi.org/10.5194/ems2021-201, 2021.

Displays

Display file

Supporters & sponsors