Erosion dynamics – precipitation relationship in the Carpathians’ Curvature region (Romania)

Abstract

The present paper analyses the relationship between the variability of precipitation and suspended sediment load (expressed as specific suspended sediment yield) during 1961-2000 period, in order to establish the role of precipitation in erosion processes and to identify the tendencies of their dynamics, in perspective of climatic changes. The scientific approach has employed the pluviometric and hydrological data (from the national hydro-meteorological network) for 7 catchments lying in the external Carpathian’s Curvature region, which is the area with the highest erosion rate in Romania. The analysis has been undertaken for each catchment, as well as for the entire region. For each catchment graphs of interannual variability of the annual precipitation and of the mean annual specific suspended sediment yield have been accomplished, on which the linear tendencies and the moving averages of the two parameters during a 10 years period have been represented. The statistic significance of linear tendencies has been established by applying the Mann - Kendall test. At regional scale, two synthetic indexes (determined through Principal Component Analysis) have been taken into account, namely the synthetic index of the mean specific suspended sediment yield and the synthetic index of precipitation. The results of the accomplished analyses show that the suspended sediment load in the external Carpathians’ Curvature during the 1961-2000 period has a general descending trend, similar to that of the precipitation, which indicate the important role played by the climatic conditions in the erosion processes. This is also emphasized by the value of the linear correlation coefficient between the mean multiannual specific suspended sediment yields and the mean multiannual precipitation of the 7 study catchments (0.57), which is higher than the correlation coefficients between the suspended sediment load and other features of the river basins (mean altitude, mean slope, forest ratio). Thus, in the perspective of climatic changes, erosion processes will reflect directly the alterations of the precipitation regime. However, one must not loose sight of the fact that, apart from the precipitation amount, the erosion dynamics is influenced by other factors as well (the geological, morphological and hydrological conditions, the land use, etc.). This fact is emphasized at regional scale by the relatively low correlation between the synthetic index of the specific suspended sediment yield and that of the precipitations (R2 = 0.45), even though the correlation is statistically significant (r = 0.66) (according to the Bravais - Pearson test, for a = 0.05 risk error). At the scale of the river basins there are relatively important correlations, statistically significant (according to the Bravais - Pearson test, for the a = 0.05 risk error), between the mean specific suspended sediment yield and the maximum liquid discharges (linear correlation coefficients ranging from 0.54 to 0.81), as well as between the mean suspended sediment yield and the mean liquid discharges (linear correlation coefficients from 0.62 to 0.83), which shows the important role played by the hydrological factor in sediment transport. A more thoroughly analysis of the relationship between precipitation and erosion (expressed as the solid discharge) must take into account not only the amount of precipitation fallen during a given period of time, but also the intensity and the frequency of rainfalls, aspects that we intend to approach in the future.