The significant rise in temperature during the past decades is not the only sign of climate change. Many other climate indicators help illustrate the climate and its alterations. The most important of these parameters can be depicted in chronological progression for climatologically relevant measuring stations.
Climate indicators are available for the most important stations of the Swiss climatological network. To the extent available, they are calculated for the periods from 1864 until present and 1961 until present using homogenised data. The graphic charts are updated about one month after the end of a season.
For historical reasons, one day lasts from morning to morning (05:40 am -05:40 am UTC) in the context of precipitation. For the other parameters, one day coincides with the calendar day (00:00 to 00:00 UTC). The time series are not available for all possible combinations of climate indicator, season, period and station. An indicator is not depicted if the required meteorological parameter is not measured at the station or if the indicator always has the same value, for example zero. Dog days never occur at high altitudes and therefore, they are not illustrated at these stations. Non-selectable combinations are greyed out in the selection menu.
How have the heating days in Geneva changed?
Heating days are days on which the heating is normally on. The number of heating days is decreasing very noticeably across Switzerland. In the 1960s, heating was required on nearly 225 days of the year in Geneva, while these days, it is only required on 190 days on average. The maximum with 244 heating days was registered in 1965, and the minimum with 181 heating days in 2006.
How have the summer days in Lugano changed?
A summer day is a day with a maximum temperature of 25°C or higher. From the 1960s until present, the number of summer days in Lugano has almost doubled from 40 days to nearly 80 days. Just 21 summer days were registered in 1977, while the number was 111 in 2003.
Homogenous climate data are used whenever possible. Homogenous climate data are adjusted for effects that are not related to climate and climate change. No homogenous series are yet available for snow and indicators that are based on the duration of sunshine; they are evaluated by means of the original data.
Trends are determined as follows:
- A smooth curve (11-year Gaussian filter) and an estimate of the linear trend (dotted line) are illustrated in addition to the annual values. For count data (when the number of days is counted), this is a logistical trend; for all others, the rise of the trend line is determined by means of the Theil-Sen-estimator.
- The absolute trend in units per ten years, the relative trend (the difference of the estimate between the start and end of the time series divided by the mean of the time series) in percent as well as the significance of the trend (p-value) are shown in each case.
- The significance is determined with the nonparametric Mann-Kendall trend test. In climatology, trends with p-values smaller than 0.05 are often considered significantly different from zero.
The following literature sources were used:
- Begert M., Schlegel T., Kirchhofer W., 2005: Homogeneous Temperature and Precipitation Series of Switzerland from 1864 to 2000. International Journal of Climatology 25: 65-80. http://onlinelibrary.wiley.com/doi/10.1002/joc.1118/pdf
- Frei, C. and Schär C., 2001: Detection probability of trends in rare events: Theory and application to heavy precipitation in the Alpine region. J. Climate 14: 1568-1584. http://dx.doi.org/10.1175/1520-0442(2001)014<1568:DPOTIR>2.0.CO;2
- Kendall M.G., 1975: Rank Correlation Methods, Charles Griffin, London.
Mann H.B., 1945: Nonparametric tests against trend. Econometrika 13:245-259.
- Sen P.K., 1968: Estimates of the regression coefficient based on Kendall's tau. Journal of the American Statistical Association, 63, 1379-1389.
- Theil H., 1950: A rank-invariant method of linear and polynomial regression analysis. Netherlands Akad. Wetensch. Proc., 53, pages: 386-392 (part I), 521-525 (part II), 1397-1412 (part III).