Increasing flood magnitude, an effect of climate change or natural climate variability?

Abstract

The last two decades have seen a number of changes in the magnitude of flood events. In general, the causes of these changes have been attributed to either climate change or natural climate variability. The aim of this paper is to identify changes in the magnitude of flood events recorded in recent decades on the Trotuș River and to attempt to determine the underlying causes. The identification of changes in flood magnitude was based either on the analysis of annual and monthly peak flows or on the analysis of flows above a certain threshold. Based on these data sets, two important parameters characterizing the magnitude of a flood event were quantified: the flood magnitude ratio and the mean annual flood. The analysis of the values of the two parameters revealed that there has been a clear increase in flood magnitude since 2004. At all stations analysed, there were at least 5 flood events with a magnitude at least twice the maximum magnitude of the pre-2004 period between 2004 and 2020. As the changes in magnitude occurred quite rapidly, we believe that they are largely due to natural climatic variability and that the period after 2004 can be considered a flood-rich period.