Glacier monitoring is very important for Switzerland as it serves as the basis for studies on the effects of climate change, the water balance and protection against natural hazards. The Glacier Monitoring in Switzerland (GLAMOS) network pursues the goal of long-term and regional monitoring of Switzerland's glaciers. GLAMOS receives financial support from the Federal Office for the Environment, the Federal Office of Meteorology and Climatology (MeteoSwiss) in the framework of GCOS Switzerland, and the Swiss Academy of Sciences and is operated by ETH Zurich, the University of Fribourg and the University of Zurich.

The systematic documentation and monitoring of mountain permafrost is increasingly important as an indicator of climate change and a natural-hazard trigger. The aim of the Swiss Permafrost Monitoring Network (PERMOS) is to systematically monitor mountain permafrost in Switzerland. PERMOS receives financial support from the Federal Office for the Environment, MeteoSwiss in the framework of GCOS Switzerland, and the Swiss Academy of Sciences. It is operated by the PERMOS partner organisations, the universities of Fribourg, Zurich and Lausanne, ETH Zurich, the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) and the WSL Institute for Snow and Avalanche Research (SLF).

As well as playing a crucial role as a climate factor, snow cover is a key economic parameter for tourism, water management, hydropower, agriculture and transport. Snow water equivalent (SWE) refers to the amount of water (in millimetres) contained in a snowpack, which also corresponds to the weight of the snowpack (in kg/m²).

SWE measurements in the Wägital

The SWE time series in the Wägital valley is the world's longest-standing for any catchment area, dating back to 1943. Furthermore, totaliser measurements have been taken in this area since 1925/1926. With a view to ensuring that these time series continue to be collected, MeteoSwiss has been supporting the gathering of these data since 2010 in the framework of GCOS Switzerland. The monitoring network, originally managed by ETH Zurich, has been operated by the company Meteodat GmbH since 1998.

Snow water equivalent measurements in the Swiss Alps

The snow stations in the Swiss Alps provide a data source unique in its quality, length and coverage regarding the spatio-temporal variability of the snowpack in the Alpine region. The WSL Institute for Snow and Avalanche Research (SLF) is maintaining long-term snow water equivalent (SWE) time series, which among others are used for snow load codes and hydrological forecasting. As there was some doubt surrounding the future of these measurements, MeteoSwiss decided to provide financial support in the framework of GCOS Switzerland for 11 of these stations.

The data that historical documents provide about past weather and climate observations are a key resource for climate research. In the Euro-Climhist database, daily weather recordings (observations and instrumental measurements), news on natural disasters and extreme weather events and phenological data from the Middle Ages to the present day are logged, stored, analysed and made available to researchers. In a bid to ensure the long-term operation, development and expansion of Euro-Climhist at the University of Bern's Institute of History, MeteoSwiss has been providing support for this database since 2010 in the framework of GCOS Switzerland.

Global glacier monitoring is of crucial importance for climate observation. Glaciers are key climate indicators and play a central role in the regional water balance and changes in global sea levels. As an international data centre, the World Glacier Monitoring Service (WGMS), based at the University of Zurich's Department of Geography, collects standardised observations on glacier fluctuations and inventories and makes them available to researchers. MeteoSwiss has been providing financial support for the operation of the WGMS since 2010, in the framework of GCOS Switzerland.

The Global Energy Balance Archive (GEBA) is a database providing a central repository of information from around the world about energy fluxes measured at the Earth's surface. GEBA data are used in many studies, for example to quantify the global energy balance, validate climate models and satellite datasets and analyse changes in energy fluxes in the context of global climate change. They are also used in the solar power, agriculture and water management sectors. The future operation of GEBA at ETH Zurich has been safeguarded since 2019 by MeteoSwiss's financial support for the archive in the framework of GCOS Switzerland.

Soil moisture and evaporation from land are two essential climate variables (ECVs) defined by GCOS. They affect the exchange of moisture and energy with the atmosphere and play a crucial role in the development of the summer droughts and heatwaves that are a feature of our current climate and are likely to become more pronounced in future. The SMiLE-ECV-CH project will produce an assessment of the potential provided by soil moisture and evaporation observations in Switzerland, focusing on four main topics: performing quality control; determining the land-water balance in Switzerland; investigating the suitability of satellite measurements of the variables; and examining land-atmosphere interactions in dry and wet periods.

Switzerland has two long temperature series, from Basel and Geneva, dating back to the mid-18th century. A third, 200-year-long series covers the Great St Bernard Pass. These series are often used to place current climate change in a long-term context. However, before 1864 the Basel and Geneva series are largely based on daily data, which were processed in the 1950s and 1960s. Swiss Early Instrumental Measurements for Studying Decadal Climate Variability (CHIMES), an ongoing Swiss National Science Foundation (SNSF) project at the University of Bern, has yielded a host of additional series for Basel and Geneva, complementing the existing series and enabling quality checks to be carried out. Most of the original data sheets have already been imaged and digitised. As part of the current project 'Long Swiss meteorological series', the University of Bern will digitise the remaining series for the three sites and conduct quality control. This additional information will allow a more accurate assessment to be made of the pre-industrial climate in Switzerland and its variability.

The 'Operational near-real-time glacier monitoring' project aims to provide observation- and model-based information on the state of Swiss glaciers, with a particular focus on the glaciological mass balance. By providing near-real-time information, the project seeks to satisfy the need for knowledge expressed by the media and public each year, especially in the summer months. The project brings together the key aspects of observation, modelling and communication.

Measurements using electrical resistivity tomography (ERT) make it possible to detect permafrost, i.e. continuously frozen ground, thanks to the very different electrical properties of frozen and unfrozen subsoil. However, the cost of this technique means that there is little continuous ERT monitoring of permafrost worldwide. One of the exceptions are six permafrost sites in the Swiss Alps that have been constantly monitored with ERT in the context of the Swiss Permafrost Monitoring Network (PERMOS) since 2005, enabling analysis of the long-term change in the soil's ice content and associated depergelation or freezing processes. In addition, though, there are many permafrost sites (estimated at more than 500) where one-off ERT measurements have been performed in the past. The aim of the REP-ERT project is to demonstrate the potential of these datasets for the climatological analysis of permafrost areas and to preserve them for future repeat measurements by incorporating them into a shared database.

Glaciological measurements in Switzerland go back a long way. Some of the time series were started in the 19th century, making them among the world's longest glaciological series. To ensure the quality and interpretability of long data series, it is absolutely vital that historical glacier data are stored and documented appropriately. While the information collected today is accompanied by detailed metadata, for 20th-century measurements these are only available to a limited extent, if at all. Accurate documentation is essential to make a consistent re-evaluation of the time series with proper quality control and to estimate uncertainties.

This project will process all direct measurements of the mass balance of Swiss glaciers since the start of the 20th century in full and in detail. This means tracking down the original observations in the archives and compiling various types of information about details such as measurement techniques, assumptions made and when field surveys were carried out. The data and metadata will then be stored in an extensive database, allowing for a more detailed and carefully documented re-evaluation of long-term time series on the glacier mass balance, making them of greater use for global climate monitoring.

In climatology, sunspot activity recordings are used for the long-term reconstruction of solar radiation, as the number of sunspots correlates closely with total solar radiation. The Specola Solare Ticinese solar observatory has systematically monitored sunspots since its establishment by ETH Zurich in 1957. Since 1981, its operations have been supported by a local association set up for this purpose called the Associazione Specola Solare Ticinese (ASST). In the context of this project, financial support is provided for collaboration between the ETH Zurich Library and ASST to ensure the long-term archiving, digitisation and publication of historical sunspot images and data.

By 2100, due to global warming, the volume of Swiss glaciers will decrease by about 90% since 1985. This represents a massive change in the Alpine region, leading to the formation of several hundred new mountain lakes in previously glaciated areas. In the framework of the AlpineWELLS project Eawag will generate an inventory of glacial lakes for Switzerland and reconstruct the genesis of these lakes, potentially back to the 19^th century. The project also aims at establishing a monitoring strategy for glacial lakes, including measurements of vertical temperature gradients, water level, and turbidity. Furthermore, bathymetry measurements are carried out to estimate water volume as key natural hazard aspect. Changes and quality of results will be assessed using existing measurements and products. The main results from this project will be a recent inventory of alpine glacial lakes in Switzerland and their change in the past two decades, an assessment of the feasibility of additional ECVs for alpine lakes using in situ measurements and EO techniques, and guidelines for the practical implementation.

Water vapor in the UTLS (Upper Troposphere and Lower Stratosphere) is a prominent Essential Climate Variable (ECV) that critically contributes to characterizing Earth’s climate and plays an important role in stratospheric dehydration, troposphere-stratosphere exchange processes, and the formation of cirrus clouds. However, in situ humidity measurements in the UTLS are still very challenging and carry significant uncertainties. The Albatross project is based on our recently developed QCL spectrometer for the measurement of water vapor in the UTLS. This spectrometer showed excellent performance in laboratory experiments and during two demonstration flights. Albatross will complement these results with the following activities: (i) further improvement of the mechanical and optical design, (ii) validation of the instrument with SI-traceable methods, and (iii) application of the new measurement technology for water vapor measurements in the UTLS. This work is carried out in close cooperation with METAS, MeteoSwiss, and the GRUAN Lead Centre in Lindenberg (Germany).

Switzerland stands out as one of the countries with the longest records of glacier changes, and long-term observations are crucial in order to understand the impact of glacier retreat on water resources or hydropower production. Despite this importance, only a few dozen of glaciers have observations extending further back than three decades. The aim of this project is to process a unique archive of several thousand historical terrestrial images in order to document glacier area, length and volume changes at a centennial scale. The photographs were acquired in the 1920s until 1940s by the Federal Office of Topography (swisstopo) to generate historical maps. A 3D-representation of the largest Swiss glaciers will be reconstructed from stereoscopic image pairs and using modern photogrammetric techniques. These will then be compared to modern topography and yield an estimate of the total ice volume change.

The Baseline Surface Radiation Network (BSRN) is one of several international networks to coordinate the measurement and archiving of radiation data. On a national level, MeteoSwiss conducts radiation measurements at four stations following similar BSRN guidelines. Longwave radiation measurements are conducted with pyrgeometers traceable to the World Infrared Standard Group (WISG) at PMOD/WRC, Davos. The following project will develop methods for the traceability of long-wave radiation measurements to all data stored in the BSRN archive. The planned activities in the project form the basis for a comprehensive traceability of the long-wave radiation data of the worldwide BSRN network to the International System of Units (SI).

This project aims to generate a 40-year fractional snow cover time series for Switzerland based on Advanced Very High Resolution Radiometer (AVHRR) satellite data, archived at the University of Bern. By doing so, it overcomes missing spatial information in Switzerland's dense measurement network of stationary in-situ instruments. Spatial and temporal analysis of the novel snow cover time series for the time period 1981 until 2021 will improve our understanding of the variability and changes of Alpine snow cover. Further analysis of the new data set will be in close cooperation with Climate Evolution, MeteoSwiss and serve as improved basis for climate services to enhance our process understanding in the field of snow cover dynamics and its impact on local society. The new data set will be public available and supports climate studies as an independent data source on snow cover dynamics.

Addressing high-mountain challenges requires the provision of actionable information on Alpine changes. Swiss national monitoring programmes for glaciers and permafrost, GLAMOS and PERMOS, play a fundamental role in the provision of this information, however often lack sufficient real-time in-situ information to develop timely monitoring products.

The present project is about exploring the potential of modern observation methods to fill this information gap, and in particular evaluating the power of crowdsourcing for long-term mountain monitoring. To this end, MountaiNow – a collaborative platform for sharing mountain observations in real-time – is built upon to provide both GLAMOS and PERMOS with relevant crowdsourced observations. This is made possible by enhancing national collaboration between the public and private sectors, building on existing infrastructure and technology, and putting together a strong multidisciplinary consortium with in-depth experience in the science, technology, communication, and policy components of mountain monitoring.

The project applies a new method for estimating the rain rate, which can be derived from observations of microwave radiometers in Bern, Payerne and Schaffhausen. The project works in close cooperation with MeteoSwiss, which runs the operation of the HATPRO radiometers in Payerne and Schaffhausen. The time series of the rain rate for the TROWARA radiometer are established in Bern (since 2004) and for the HATPRO radiometers in Payerne and Schaffhausen (since 2007) and compared with coinciding measurements of conventional rain gauges. The time series are harmonized to detect possible trends in the rainfall rate. The algorithm for the rain rate is implemented for the operational data processing of the rain rate for the three microwave radiometers, thus enabling a monitoring of the rain rate in near real-time. Furthermore, it is planned to set up a HATPRO radiometer at the University of Bern to perform further comparisons between different measurement techniques.

Securing long-term permafrost monitoring at the Tsaté site in the framework of PERMOS

The systematic documentation and monitoring of mountain permafrost in the Swiss Alps is handled by the Swiss Permafrost Monitoring Network (PERMOS). The extreme conditions in a high Alpine environment mean that the measuring systems have to be regularly overhauled or even completely replaced. An example of this was the 2004 borehole at Tsaté, where there were increasing inconsistencies in the temperature time series. It was not feasible to calibrate or replace the thermistor string, which was stuck in the borehole. Instead, in the framework of GCOS Switzerland, MeteoSwiss provided support to enable the University of Lausanne to replace the borehole.

Quality analysis and classification of Swiss phenological series

Plant growth and development are substantially affected by climate conditions. It follows that phenological observations are key climate indicators. Across Switzerland, a total of 12 stations belonging to the phenology network were surveyed in the framework of GCOS Switzerland. In this project, the University of Bern's Institute of Geography contributed to GCOS Switzerland by examining this selection of the most valuable phenological stations and series.

Processing and standardising historical time series documenting length variation in Swiss glaciers

In the context of glacier observation since the 1880s, the change in the glacier tongue position was systematically documented, and the length variation was worked out from this. However, the length variation data were not georeferenced and were often incomplete. Therefore, this project run by ETH Zurich systematically processed and standardised the historical length variation time series.

Development of a communications strategy for the Swiss cryospheric monitoring networks

The Swiss cryospheric observation network covers glaciers, snow and permafrost and is an integral part of long-term climate monitoring in the Swiss Alps. Promoting public awareness of the importance of climate observation is a key factor that will help to safeguard the climate time series over the long term. Therefore, this project run by the University of Fribourg brought together all the partners involved in cryospheric monitoring networks to work out the basic components of a joint communications strategy.

Quality assurance of long-term snow water equivalent measurements

Snow water equivalent (SWE) measurements play a key role in flood forecasting, snow load standards and the validation of remote sensing data. SWE data are currently collected manually. However, not only is this very time-consuming but it is becoming increasingly difficult to find staff to consistently conduct measurements throughout the season. Therefore, as part of this SLF project, several automated monitoring techniques were compared with conventional measurement instrumentation.

Comparison of spatially high-resolution measurements of snow distribution using manual and laser- and drone-based measurements in the Wägital

The time series covering snow density, snow water equivalent and snow depth for a catchment area in the Wägital valley is longer than any other in the world. However, manually recording snow depth is fraught with considerable uncertainties. One alternative is drone-based monitoring, enabling cost-effective, high-resolution estimates of snow depths. The aim of this joint SLF/Meteodat GmbH project was to evaluate the potential of this drone-based method.

Integrated Monitoring of Ice in Selected Swiss Lakes

Freezing and thawing data recordings for lakes provide valuable insights into the regional climate and help with the development of hydrological models. However, a lake's size and geographic location may mean that not all observation methods are equally suited to the task. This means that a careful evaluation of the available methods is needed. Therefore, MeteoSwiss supported a feasibility study in the framework of GCOS Switzerland that compared the effectiveness of satellite images, webcams and in-situ measurements in monitoring lake ice. This project was conducted by ETH Zurich, the University of Bern and the Swiss Federal Institute of Aquatic Science and Technology (Eawag).

Integrated Lake Ice Monitoring and Generation of Sustainable, Reliable, Long Time Series

Freezing and thawing data recordings for lakes provide valuable insights into the regional climate. However, a lake's size and geographic location may mean that not all observation methods are equally suited to the task. Based on a previous feasibility study on lake ice, this project run by the ETH Zurich integrated various sensors and methodologies to operationally obtain systematic and reliable observations of lake ice.

Providing Data Provision for a Sensitivity Analysis of Snow Time Series

Like all climate series, snow time series covering many years are affected by changes in measuring locations, observers and measurements techniques. Such non-climate changes may have an influence on any trends that are identified. The project Providing data provision for a sensitivity analysis of snow time series collected data for a sensitivity analysis of snow measurements with respect to non-climate effects. Moreover, thorough metadata compilation allowed WSL SLF to collect information on the history of snow fall and snow depth measurement practices in Switzerland and other countries.

GNSS sensors’ suitability for the automated operational measurement of snow water equivalent in the Swiss Alps

Snow is an essential climate variable that is characterised not only by its depth but also by snow water equivalent (SWE). This is traditionally determined by weighing a snow sample. Recent studies have shown that the SWE can also be worked out using signals from the Global Navigation Satellite System (GNSS). The SWE can be deduced from the difference in signal characteristics that GNSS receivers record above and below the snowpack. In the framework of this project, the SLF in collaboration with its partners assessed the suitability of the automated operational measurement of SWE within the Swiss observational network for SWE.

The Global Atmosphere Watch (GAW) Precision Filter Radiometer Network

Aerosol optical depth (AOD) is an essential climate variable of great importance to climate and atmospheric research, as it is one of the main parameters determining the Earth's radiative forcing. AOD is measured using precision filter radiometers (PFRs), thereby contributing to the Global Atmosphere Watch (GAW) programme. The World Aerosol Optical Depth Research and Calibration Centre (WORCC) of the Physical Meteorological Observatory in Davos (PMOD) maintains the PFR standard for measuring AOD. Therefore, this project run by the PMOD/WRC (World Radiation Centre) concluded on harmonization, re-evaluation and improvement of the GAW-PFR AOD time series.