Natural climatic changes and solar cycles: an analysis of hydrological time series

The effects induced on the climate by human activity have become a major is sue for the new millennium. In order to arrive at sustainable conclusions i t is necessary, first of all, to assess and quantify natural climatic chang es. In general this is done by analysing available time series. In the case of historical hydrometeorological data sets, a comparative analysis with s olar cycles is not usually conducted. This work, however, demonstrates that the effect of solar cycles observed at the Equator is also visible at midd le and high latitudes with multiple periodicity of the basic solar frequenc y (roughly 11 years). This could well be due to the interaction between sol ar forcing and circulation mechanisms within the atmosphere, i.e. water-air -soil interactions coupled with anthropogenic forcing. This theory has been tested by comparing different types of historical data series with the Riv er Po discharges and cyclic appearance of slime bloom in the Adriatic Sea.