Temporal variation of water discharges in the lower course of the Danube River across the area from Reni to Izmail under the influence of natural and anthropogenic factors

Abstract

The Danube River mouth is a main source for fresh water used for water supply and irrigation purposes in the arid southern part of Ukraine. In addition, the water of the mouth is used for filling the Danube Lakes. Climate change and numerous social and economic factors reduce the area and the water level of the Danube Lakes and increase their salinity. Under these circumstances the water exchange between the Danube River and the lakes is a very important process which allows maintenance of the water–salt balance of the latter. Such water exchange massively depends on the Danube River regime. The paper presents research of temporal variation of typical water discharges in the lower course of the Danube River associated with assessment of natural and anthropogenic factors affecting river runoff fluctuations. Time series of annual average water discharge at the water gauging stations of such cities as Reni and Izmail were considered uniform for the selected periods. They cover the period of conventionally natural river runoff regime (1840–1920), the period of the least altered river runoff regime (1921–1960) and the most altered river runoff regime under a heavy anthropogenic influence (1961–1989). The analysis of the impact of climate changes on the river runoff allowed introduction of a new, modern period of the Danube River hydrological regime (1990–2015). It is established that the series of maximum and minimum water discharges are characterized by the lack of their uniformity from the beginning of the period of initial influence of hydraulic engineering structures on the hydrological regime (since 1961). The analysis of the aggregate multi-year series (1840–2015) of average annual, maximum and minimum water discharges of the Danube River across its length from Reni to Izmail showed the presence of positive trends. At the same time the period of climatic changes (after 1989) is characterized by a less intensive growth of maximum water discharges. The research resulted in establishing the periodicity and synchronism of water discharge fluctuations in the lower course of the Danube River from Reni to Izmail within the territory of Ukraine. In particular, the study showed for the first time that from the 2000s onwards the redistribution of river runoff between the Danube River branches led to unsynchronization of minimum river runoff in different parts of the Danube Delta. The research shows that comprehensive analysis of the Danube River hydrological regime under modern climatic conditions is required to ensure efficient engineering regulation of the Danube Lakes filling pattern. Such regulation, in its turn, will ensure that the water supply and irrigation purposes are achieved.

Impact of climate change and human factors on the water regime of the Danube Delta

“…It is concidered (Panin and Jipa, 2002;Olson and Krug, 2020;The Lower Danube River..., 2022) that the catchment area of the Danube River is 817,000 km 2 and the length is 2860 km. There are also slightly different data (Habersack et al, 2013;Stagl and Hattermann, 2015;Romanova et al, 2019), but the difference is small. The water regime of the Danube River and, in particular its delta, largely depends on climate, which is unstable.…”

“…The important issue of the lower course of the Danube River is water runoff and its distribution by the delta branches. This issue is considered in the works (Mikhailova et al, 2002;Hydrology..., 2004;Gastescu, 2009;Romanova et al, 2019). However, the distribution of runoff is unstableit changes due to natural and anthropogenic factors.…”

Monthly stream temperatures along the Danube River: Statistical analysis and predictive modelling with incremental climate change scenarios

“…As mentioned previously, the earliest recorded observations of the water levels on the Danube River can be traced back to 1821. The study utilizes the longest data series available, which was derived from the Stein Krems/Kienstock station on the Danube (1829-2020 as shown in Figure 4c), followed by data from Orsova and Reni (1840-2020) (Romanova et al, 2019). Despite the overall increase in air temperatures since 1870, the flow rates of the Danube exhibit cyclic fluctuations of approximately 28-30 years (Figure 7) along the entire length of the river.…”

“…Unlike air, water has an exceptionally high specific heat capacity; its temperature can be considered a stable indicator of long-term trends (Pekárová et al, 2022(Pekárová et al, , 2008. In this respect, Romanova et al (2019) called attention to the fact that, in general, there are some common long-time trends in climate change for the countries of the Danube River Basin. These changes include an increase in the average annual air temperature, resulting in a decrease in the percentage of snow in the total annual amount of precipitation.…”

Hydrological analysis of the Danube regime on the section through the Republic of Croatia and the Republic of Serbia

“…analysis of the Danube flow regime (in Slovakia) through the period from 1840 to 2015 was presented by Pekarova et al (2019). Romanova et al (2019). investigated natural and anthropogenic impacts on the course of the Danube in the area from Reni to Izmail.…”