Key climate indices in Switzerland; expected changes in a future climate

Elias M Zubler,Simon C Scherrer,Christof Appenzeller,Mark A Liniger,Mischa Croci-Maspoli

doi:10.1007/s10584-013-1041-8

Elias M Zubler, Simon C Scherrer + Show 3 more

Open Access

https://doi.org/10.1007/s10584-013-1041-8

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Abstract

Abstract Climate indices facilitate the interpretation of expected climate change impacts for many sectors in society, economy, and ecology. The new localized data set of climatic change signals for temperature and precipitation presented by Zubler et al. (Clim Change, 2013) is applied for an analysis of frequently used climate indices in Switzerland. The indices considered are: number of summer days and tropical nights, growing season length, number of frost days and ice days, heating and cooling degree days, and the number of days with fresh snow. For the future periods 2020-49, 2045-74 and 2070–2099 the indices are computed using a delta-change approach based on the reference period 1980–2009 for the emission scenarios A1B, A2, and RCP3PD. The scenario data suggest the following relevant findings: (1) a doubling of the number of summer days by the end of the century under the scenarios A1B and A2, (2) an appearance of tropical nights even above 1500 m asl, (3) a possible reduction of the number of frost days by more than 3 months at altitudes higher than 2500 m asl, (4) a decline of heating degree days by about 30 % until the end of the century, and (5) the near disappearance of days with fresh snow at low altitudes. It is also shown that the end-of-the-century projections of all indices strongly depend on the chosen emission scenario.

Highlights

Introduction and motivationClimate indices facilitate the interpretation of the impacts of climatic change on ecology, economy and society
The Expert Team on Climate Change Detection and Indices (ETCCDI), which is the joint responsibility of the World Meteorological Organization (WMO), the World Climate Research Programme (WCRP) and the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM), has defined a set of indices that describe the manifold facets of climatic change (Klein Tank et al 2009)
We evaluate the future development of some key indices over Switzerland for the periods 2020-49, 2045-74 and 2070-99 with respect to the reference period 1980–2009, using the spatially localized gridded data set providing probabilistic temperature and precipitation change signals presented by Zubler et al (2013)

Summary

Introduction and motivation

Climate indices facilitate the interpretation of the impacts of climatic change on ecology, economy and society. The following indices are considered here: Number of summer days: Average number of days per year with maximum temperatures ≥ 25 ◦C. Thermal growing season length: Average number of days in a year between the first occurrence of a 6-day period with daily mean temperatures > 5 ◦C and the first occurrence after July 1 of a 6-day period with daily mean temperatures < 5 ◦C This index is important for agriculture and ecology. Heating degree days: Annual average sum of differences between outside daily mean air temperature (Tair,i) and the base temperature inside the building (Troom = 20 ◦C). Cooling degree days: Annual average sum of differences between outside daily mean air temperature (Tair,i) and the base temperature (Tcooling) of 18.3 ◦C (American Society of Heating Refrigerating and Air-Conditioning Engineers 2001), above which cooling is assumed to be needed in buildings.

General remarks

Diagnosing the number of days with snowfall

Results

Temperature-based indices

Precipitation-based indices

Discussion and conclusions