Hydro-CH2018 in HADES
The present platform, “Hydro-CH2018: Scenarios till 2100”, presents research results of the
Hydro-CH2018 and CH2018 projects in a form that is suitable for dealing with applied hydrological questions. The platform was developed by the producers of the
Hydrological Atlas of Switzerland (HADES) and is structured analogously to the atlas’s
“Data and Analysis Platform”. It presents hydro-climatic and hydrological scenarios for the 21
st century. The platform currently includes
precipitation and
temperature scenarios, estimates of
glacier development, the resulting runoff scenarios for selected catchments (map topics
L01,
L02 and
L03), and water body temperature scenarios (
L05 und
L06) up to 2100.
For Switzerland to adapt to climate change, detailed knowledge is needed about the possible effects on waterbodies and on the water balance. The Federal Council has therefore commissioned the Federal Office for the Environment to provide hydrological bases for adaptation measures. These include expanding the knowledge of hydrological processes, documenting the changes already observed, and calculating future scenarios, some of which are presented on this platform.
The Federal Council’s mandate was implemented as part of the priority theme
“Hydrological bases of climate change Hydro-CH2018” of the
National Centre for Climate Services (NCCS; see box). The initiative was abbreviated “Hydro-CH2018” because it is based on the
latest climate scenarios, entitled “CH2018”. Comprising eleven research projects and literature studies, the initiative involved numerous leading Swiss institutions specialised in water research.
Compared to previous studies on the effects of climate change on Switzerland’s hydrology, Hydro-CH2018 was able to draw on improved data and methods. For the first time, the CH2018 climate scenarios provide continuous (transient) data series in daily – and spatially high – resolution for the years 1981–2099. These new data, in particular, enable a more in-depth and quantitative analysis of future changes. Further information on the Hydro-CH2018 project can be found in the
synthesis report and the accompanying
brochure.
National Centre for Climate Services (NCCS)
The NCCS is the Swiss federal network for climate services. As a national coordination and innovation body and knowledge hub, the NCCS supports climate-smart decision-making in order to minimise risks, maximise opportunities, and optimise costs.Hydrological scenarios
The hydrological scenarios are part of a whole
model chain: It starts with various emission scenarios that describe possible future courses of greenhouse gas emissions at the global level. These emission scenarios were combined with global and ultimately regional climate models to create, using statistical methods, local climate scenarios for Switzerland (CH2018), using statistical methods. From these regional models, the hydrological models then used data such as precipitation and temperature to calculate the hydrological scenarios in “Hydro-CH2018”. The hydrological scenarios show possible ways in which the water balance and waterbodies in Switzerland could, under certain assumptions, change as a result of climate change. They include important hydrological components such as discharge, groundwater recharge, proportion of meltwater, evapotranspiration, or waterbody temperatures. At the end of the model chain are impact models that simulate the effects on water management or agriculture.
Schematic representation of the entire model chain for estimating the effects of climate change on water management
The term RCP (Representative Concentration Pathway) is an international abbreviation for labelling globally defined scenarios of greenhouse gas emissions. To illustrate the effectiveness of international climate protection measures and show the range of possible future changes, the following three emission pathways were used in Hydro-CH2018:
- RCP 2.6 or “concerted mitigation efforts” (often referred to as “with climate mitigation measures” in the accompanying texts to the maps) stands for a future in which the international community implements effective climate mitigation measures in accordance with the Paris Climate Convention. By drastically reducing emissions, global warming of the atmosphere will be limited to less than two degrees compared to the pre-industrial era.
- RCP 4.5, or “limited mitigation”, stands for a future in which greenhouse gas emissions are curbed, but the level in the atmosphere continues to rise for another 50 years. The two-degree target is missed.
- RCP 8.5 or “no mitigation” stands for a future without effective climate mitigation measures, in which global greenhouse gas emissions continue to rise sharply and global warming reaches 4 to 5 degrees by the end of the century.
More information on the emission scenarios can be found on the
NCCS website.
IPCC Representative Concentration Pathways
Global climate models are used to calculate the effects of different scenarios of greenhouse gas emissions on the global climate. Their spatial resolution is fairly coarse. To achieve a higher resolution, the results from the global models are used as boundary conditions for simulations using higher-resolution regional climate models over Europe.
The CH2018 climate scenarios use regional climate model simulations from
EURO-CORDEX, the European branch of the CORDEX initiative. In a climate model simulation, one of nine global climate models is linked to one of seven regional climate models. The regional climate models use a spatial resolution of 12 km * 12 km or 50 km * 50 km. Comparing the different climate model simulations allows an estimation of the uncertainties associated with climate scenarios.
For Switzerland, which is small and mountainous, the spatial resolution of the regional climate models is still too coarse to be used directly for hydrological models. Using a statistical procedure (downscaling), the relatively coarsely resolved regional climate model data were corrected on the basis of measured values and adapted to local scales. CH2018 features these climate data for various climate parameters as time series at existing meteorological stations. In addition, area-wide maps with a grid resolution of 2 km * 2 km were produced for daily temperature values and precipitation totals. All time series and grid data are available for the entire period of 1981–2099 in a daily resolution (
www.nccs.ch).
Models used
In Hydro-CH2018, the selected hydrological model depended on the parameters investigated. Detailed data and further information can be found in the text accompanying each map (via the information button
). Depending on the hydrological model, only a limited number of model simulations could be carried out, as not all climate parameters required for the hydrological models are available in all climate models. The number and selection of model chains for the maps shown in HADES may therefore differ, depending on the hydrological model used.
Area of investigation
Hydro-CH2018 investigated the whole of Switzerland, the Principality of Liechtenstein, and certain other neighbouring areas that drain into Swiss territory – in brief, the area collectively referred to by experts as “hydrological Switzerland”.
Time periods considered
The “present state” or the “reference period” refer to the mean hydrological state during 1981–2010. These three decades are the starting point and reference for calculation of the scenarios. All data on future changes refer to this period.
Based on the climate model simulations used, the scenarios describe the expected mean values (medians) and the range of possible changes (see
Uncertainties) of hydrological developments. In this context, mean values of periods of over 30 years are considered, grouped around the years 2035 (period: 2020–2049), 2060 (period: 2045–2074), and 2085 (period: 2070–2099).
The mean values of the 30-year periods do not show how the hydrological conditions will develop in individual years in the future. The mean value representations therefore do not include natural year-to-year variability such as wet or dry years.
Hydro-CH2018 also examined the effects of expected changes in the water balance on waterbodies and water management. The synthesis report,
synthesis report “Effects of climate change on Swiss waters”, provides a comprehensive overview of the current state of knowledge in the field of hydrology and water management, as well as recommendations for adaptation to climate change. A
brochure summarises the most important findings.
As models can only depict actual conditions in a simplified way, model results inevitably contain some uncertainties. Each step in the model chain (see
figure of the model chain)), for example, comes with an increase in the number of possible model combinations and in the complexity of the calculations. In addition, certain assumptions must be made at each step, which lead to further uncertainties; in hydrological modelling, for example, how and to what degree of accuracy the processes for discharge formation, evapotranspiration, and snow or glacier melt are to be simulated. These uncertainties multiply along the model chain, which is why, in most cases, the difference between model and reality increases along the chain. In the reference period, uncertainty can be limited by comparing the models with measured data (calibration). To estimate inherent uncertainties, projections for the future involve a comparison of the models of various universities and research institutes.
