Statistical Analysis of Hydrological Regime of the Danube River at Ceatal Izmail Station

In the present study, we focused on the statistical analysis of changes in the characteristics of the minimum, average annual, and maximum discharge series of the Danube River at Ceatal Izmail water gauge. We have processed the series of annual average discharges during the whole water stage observation period 1840–2015, as well as the average daily discharge over the period 1931–2015. Firstly, we have identified changes in commonly used hydrological characteristics (such as long-term trends and variability of the annual averages, minimum annual discharges, occurrence of extremes, etc.). In the second part we divided the annual hydrogram of the daily discharges into individual flow events (waves) and we calculated their number and their duration in each year. Specifically, we have calculated the numbers and characteristics for extremely dry periods, as well as for small and large floods. The analysis of the discharge series of the Danube River evaluated at Ceatal Izmail shows: the long-term average discharge of the Danube River in the closing profile does not change. Annual regime has slightly changed - spring discharge peaks occur in the last years about 40 days earlier. From the statistical discharge analysis, we still do not know clearly whether this is the result of higher precipitation sums due to climate change or due to the channel training - reducing flood areas and draining acceleration. In the past, fluctuations in the Danube River flow were even higher than at present, in both directions - minimum and maximum discharge were more extreme in some periods. Therefore, it is necessary to focus on historical hydrology and analyze as many observations as possible. Statistical attention to the discharge, as well as precipitation and air temperature series needs to be continued.