THE ROLE OF RIVERS IN THE SWISS NETWORK FOR THE OBSERVATION OF ISOTOPES IN THE WATER CYCLE (ISOT)

摘要

During recent decades, Switzerland has been going through the greatest change inclimate regarding temperature and the distribution of precipitation since the nationalclimate measurement and observation network was established in 1864. Water isotopes( 2 H, 3 H and 18 O) provide an important additional tool to evaluate the influence of thesechanges on the different compartments of the hydrological cycle. The Swiss networkfor the observation of isotopes in the water cycle (ISOT) comprises precipitation,river water, and shallow groundwater stations. The climatic trend of stable isotopesin precipitation, especially the distinct shift to more enriched values between 1985and 1990, is also recorded in the isotopic composition of the main rivers dischargingfrom Switzerland. However, the isotopic signature is complex, because a variety ofdifferent catchment and discharge characteristics (glaciers, snow cover, hydro-electricregulations) are superimposed on the trends. For example, the effects of the heat wavein summer 2003 resulted the following year in more negative δ -values for all main rivers.Drought at the beginning of the year and extreme heat during the summer changed theprecipitation conditions and discharge ratios of winter to summer precipitation. Duringrecent years, there has also been a change in the behaviour of deuterium excess. It hasincreased in the River Ticino on the south side of the Alps probably as the result of agreater influence of the Mediterranean Sea as a source of moisture to the south of theAlps. The values have remained stable in rivers on the northern side of the Alps.