Kotlarski Sven

Swiss snow cover in a changing climate: Evaluation of a long-term high-resolution SWE analysis

Project Number: 4D CH-7482 / MMD 52434
Project Type: Master
Project Duration: 01/07/2022 - 06/04/2023 project completed
Funding Source: other ,
Leading Institution: ETH Zürich
Project Leader: Dr. Sven Kotlarski
Head of Climate Evolution
Climate Evolution
Analyse und Prognose - Klima
Operation Center 1
8058 Zürich-Flughafen
Phone: +41 (0) 79 718 85 45 ; +41 (0) 58 460 93 19
FAX: +41 (0) 58 460 90 01
e-Mail: sven.kotlarski(at)meteoswiss.ch

related to this project.
for which the project has a relevance.

Research Areas:

climatology, atmospheric physics, aeronomy
environmental sciences

Surface snow cover is an important and highly interactive component of global and regional climate
systems and already has clearly responded to past warming trends in many regions of the world. Moreover,
it is a key ingredient for tourism industry, water supply, irrigation, and hydro-power generation in many
mountainous and high-latitude regions. Accurate information about the past, present and future evolution
of snow cover is therefore of high importance. In Switzerland, to date, no state-of-the-art high-quality
and spatially highly-resolved data set of surface snow cover at a climatological scale exists. For this
reason, the Federal Office for Meteorology and Climatology (MeteoSwiss) and the WSL Institute for
Snow and Avalanche Research (SLF), have generated a new daily snow water equivalent (SWE) data set
(OSHD-CLQM) at a 1 km horizontal resolution, covering the hydrological years 1962 to 2022. Based on
OSHD-CLQM, the spatio-temporal snow cover variability in Switzerland as a whole, as well as for different
sub-regions and elevation classes employing a range of snow indicators is analyzed here. OSHD-CLQM
is validated against existing data from station-based surface observations and from Advanced Very High
Resolution Radiometer (AVHRR) and moderate resolution imaging spectroradiometer (MODIS) satellite
data. A case study of the Swiss National Park (SNP) is conducted to assess the performance of OSHD-
CLQM on a comparatively small area.
In accordance to previous studies, the analysis shows that the Swiss snow cover has changed strongly
over the last decades. The comparison of two climatological long-term periods, 1962 - 1990 and 1991
- 2020, in terms of the mean SWE (September - May) and the number of snow days (SWE > 10 mm)
within the snow season, demonstrates a decrease in both indicators over the majority of the country.
Low elevations (< 1000 m a.s.l.) show relative decreases larger than 50 % of the mean SWE and larger
than 30 % regarding the mean number of snow days (about - 22 days). The largest absolute difference
of the mean SWE is found at medium elevations (between 1500 - 2000 m a.s.l.) with a decrease of about
45 mm (about ? 26 %). The validation of OSHD-CLQM indicates in general a high agreement between
it and the in-situ observations. At the considered 59 measurement stations and their corresponding
nearest grid cells in OSHD-CLQM, a median correlation of 0.82 is found for the time series of the mean
SWE over the winter half year. Further, OSHD-CLQM lies within the range of AVHRR and MODIS.
However, a clear statement regarding the comparison between OSHD-CLQM and the remote sensing
data sets is difficult because of large differences between AVHRR and MODIS. Larger uncertainties and
limitations of OSHD-CLQM are found, in particularly at the highest elevations (i.e. > 3000 m a.s.l.). They
originate from different sources, such as temporal inconsistencies in the input data grids of the underlying
OSHD snow model or the lack of stations at high elevations that are needed for bias correction of the
model. Nevertheless, overall OSHD-CLQM is able to provide adequate information on past snow cover
for Switzerland as a whole, as well as for the selected sub-regions and the comparably small region of the

Danioth, S., Kotlarski, S., Muelchi, R., Gubler, S., Steger, C., Marty, C. Schär, C. (2023): Swiss snow cover in a changing climate: Evaluation of a long-term, Master's Thesis, ETH Zürich
PDF Masterarbeit

Last update: 10/11/23
Source of data: ProClim- Research InfoSystem (1993-2024)
Update the data of project: CH-7482

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