Extreme Low Flow during Long-Lasting Phases of River Runoff in the Central Part of the East European Plain

Abstract

In the rivers of the central part of the East European Plain (the Volga at Staritsa, the Oka at Kaluga, and the Don at Stanitsa Kazanskaya), long phases (10–15 years or more) of increased/decreased annual and seasonal runoff have occurred, as well as differences in the frequencies of extremely low flow conditions from the late 19th century to 2020. Phase boundaries were identified by cumulative deviation curves and statistical homogeneity. The frequencies of specific water flow values were estimated using the empirical curves of the exceedance probability of annual and seasonal water flows based on their long-term time series. In the century-long changes of rivers considered, two long contrasting phases were revealed. These phases are characterized by increased and decreased runoff of hydrological seasons. Near simultaneously, a phase of increased runoff was first observed for the freshet season. On the contrary, phases of decreased runoff were first observed for low-water seasons. The runoff phases differ significantly in duration and differences in flow. Significant differences were revealed in the frequency of low-water years for a low runoff with an exceedance probability above or equal to 75% and above or equal to 95%.

The Variation in the Water Level of Lake Baikal and Its Relationship with the Inflow and Outflow

“…These points provide a graphical representation of the transition between the different long-term phases of averages for each of the hydrological characteristics. Estimates of the shift points for contrasting phases were determined earlier for other rivers [30][31][32] by using CDCs and criteria for the uniformity of the mean values in the time series using Student's t-test [53] and the Mann-Whitney-Pettitt (MWP) test [54]. The results of identifying the shift points of the contrast phases determined using the above set of methods, as a rule, coincided [30][31][32].…”

“…However, even in this case, the inter-annual fluctuations in the annual and cold-season water discharge showed quite synchronous changes, except for the beginning of the observation period, when there were asynchronous changes for about fifteen years (Figure 5b). The presence of long-term phases (periods) of increased or decreased annual and seasonal discharge has been investigated for rivers in different regions of Russia [31][32][33]. The duration of such phases varies from 10 years to many decades.…”

“…The presence of long-term phases (periods) of increased or decreased annual and seasonal discharge has been investigated for rivers in different regions of Russia [31][32][33]. The duration of such phases varies from 10 years to many decades.…”

“…Significant attention has been paid to the problem of long-term changes in the lake levels [27][28][29]. Furthermore, an important component of multi-year changes is the long-lasting phases of increased/decreased values of various components of the water cycle [30][31][32]. As far as is known, this aspect of the time series has not yet been applied to studies of the Lake Baikal basin.…”

Changes of Hydrological Extremes in the Center of Eastern Europe and Their Plausible Causes

“…In eastern Europe, the flood frequency has been decreasing since the 1970s [3,5,6]. Westwards, in Poland, a significant decrease in winter flow has been observed in many rivers accompanied by a delayed increase in the spring thaw in the 1950s and 1960s [7].…”