Variability of river streamflows as a climatic indicator

. The variability of streamflows during the period 1900-1996 of rivers running across the country is analyzed. The emphasis is on the detection of the main low frequencies, trends and coherence between dry conditions and excess water in a group of rivers. In doing so, time series of monthly and annual streamflows of more than fifteen rivers of the region were used. After evaluating the representativeness of the series, by analyzing more than one stream-gauging station along the river bed (when it proved possible), the structure of the series through frequency spectrum and main components was analyzed. Some important trends that were already described were detected but most of them could be a result of specific climatic jumps, which were also observed in some climatic series. Different cycles are found in most series but they only maintain coherence for limited regions and certain wavelength ranges. However longer-period cycles suggest that causes should be sought in the large scale since they belong to series of rivers located in subtropical and high latitudes. The influence of ENSO on the streamflow series is examined in regional terms, Results are then compared to those obtained by other authors. Finally, coherence between extremes in the region is studied as a climatic indicato