The temperature of groundwater is one of its most important characteristics, and a key factor influencing its hydrochemical and biological state. It affects the dissolved oxygen content of the water, as well as the degree of mineralisation. At higher temperatures there may also be an increase in microbial activity – an indicator of groundwater quality. With climate change, in particular, in mind, it is important to monitor how groundwater temperature changes over time.
In a long-term comparison, 2015–19 was a period in which groundwater temperatures tended to be higher than average. Indeed, high temperatures were recorded at just over half of measuring sites in 2018 and 2019, although it is not yet possible to identify any consistent trend periods of several years of low or high groundwater temperatures alternate with a certain regularity. For this reason, the indicator is not evaluated at present.
The CH2018 Climate Change Scenarios suggest that we can assume that the frequency, duration and intensity of hot periods are likely to increase in the long term. Direct anthropogenic factors, such as infrastructure or the use of geothermal energy, can also have a regional effect on groundwater temperature. A slight increase in groundwater temperature, as reflected in the indicator, can be expected overall over time.
- Related indicators
- Temperature of watercourses
No standard indicator exists at present in international indicator systems such as that of the EEA. Certain countries currently take similar approaches, however. Austria is one example here.
In a year-by-year comparison, the indicator provides a nationwide overview of the incidence of low, normal and high groundwater temperatures.
The data is supplied from the measuring sites serving the QUANT module of the NAQUA National Groundwater Monitoring programme (around 50 operated by the federal government, and 50 by the cantons), which continuously monitor groundwater temperature. The indicator is based on a calculation of the percentage of the annual number of measuring sites recording low, normal or high temperatures. The mean annual temperature is determined for each individual measuring site, and compared with the corresponding 10th or 90th percentile over 20 years. If the annual mean is below the 10th percentile for 20 past observation years, groundwater temperature is described as low, and if it is higher than the 90th percentile it is termed high. The groundwater temperature is said to be normal if the annual mean lies between the 10th and 90th percentiles.