N. L. Frolova

Climate-induced changes in groundwater runoff in Don basin

The natural-climatic causes of changes in river runoff and seasonal recharge of groundwater in Don basin are considered. Joint analysis is made of changes in the statistical characteristics of the series of air temperature and precipitation, mean annual and dry-season-averaged runoff for both the entire observation period and of periods 1940–1969 and 1970–2000 with comparable durations. The presence of statistically reliable ascending trends in air temperature, precipitation, and dry-season (groundwater) runoff for period 1970–2005 is demonstrated. Climatic changes in Don basin also have their effect on the formation of extremely low water in small and medium rivers, including cases of zero runoff. Zoning of the territory by runoff formation conditions is carried out, and new estimates of natural groundwater resources in Don basin for period 1970–2000 are constructed. Appropriate maps are compiled.

Specific features of ice regime in rivers of the Northern Dvina basin

Variations in the characteristics of ice regime of rivers in the Northern Dvina basin over the last 125 years are analyzed. For the Northern Dvina lower course, potential changes in the dates of the appearance of floating ice and the breakup due to expected changes in the air temperature and the rate of streamflow in rivers are assessed. Special attention is paid to the factors that affect the formation of ice jams and their spatial and temporal variability. The prognostic relationship for the maximum ice-jam stage in the Sukhona River near the town of Velikii Ustyug is presented as an example.

Dangerous ice phenomena on the lowland rivers of European Russia

In the Russian climate, the security of populations and economic security are often limited by dangerous ice phenomena. Not only ice-jam floods, but also some processes lead to the violation of operating conditions of various facilities (water intakes, roads, bridges) and damage hydraulic structures and shipping. Currently, rivers’ ice regime characteristics change under the influence of both natural (primarily climatic) and anthropogenic factors. Changes have been analyzed in detail on the basis of observations of 300 hydrological stations in the period from 1936 to 2013. Changes of ice phenomena hazards have been estimated. Hazard assessment of flooding caused by ice jams has been carried out for the Northern Dvina River reach from the Velikiy Ustyug City to Kotlas, the most problematic ice jam flooding area in European Russia. The modeling was performed on the basis of STREAM_2D software complex for current conditions and taking into account the possible construction of various protective structures. Methods for the prevention of negative impact of water at the site are examined.

Current Changes in River Water Regime in the Don River Basin

The formation and distribution of present-day water resources under the effect of changing climate are studied. Seasonal, annual, and many-year variations in the regime of spring-flood and dry-season runoff of rivers with drainage areas from 2000 to 20000 km2, reflecting the zonal landscape-climatic conditions of runoff formation, are considered. It is shown that various and often contradictory demands of water users to water supply distribution over seasons of the year result in that the entire water management complex depends on not only the total volume of water resources, but also on the water regime characteristics of rivers in different phases of hydrological year. It was established that the climate changes recorded in the recent decades radically change the pattern of space and time variations in runoff characteristics.

Many-year variations of river runoff in the Selenga basin

Many-year variations of river runoff in the Selenga basin are analyzed along with precipitation, potential evapotranspiration, and basin water storages. Data of ground-based (1932–2015) and satellite observations, as well as the analysis of literature data suggest the presence of within-century cycles in the series of annual and minimum runoff. Compared with 1934–1975, the Selenga Basin shows a general tendency toward a decrease in the maximum (by 5–35%) and mean annual (up to 15%) runoff at an increase in the minimum runoff (by 30%), a decrease in the mean annual precipitation (by 12%), and an increase in potential evapotranspiration by 4% against the background of a decrease in evaporation because of lesser soil moisture content and an increase in moisture losses for infiltration because of permafrost degradation. The observed changes in water balance may have unfavorable environmental effects.

Water isotopic-geochemical composition in the Trekhtsvetnoe meromictic lake on the White Sea coast

The isotopic features of Lake Trekhtsvetnoe in the White Sea coast area were studied in 2012–2015 in both winter and summer. Lake Trekhtsvetnoe is a water body, separating from the sea, with constant vertical stratification throughout the observation period. Its isotopic, hydrophysical, and biological characteristics have been studied. By the isotopic profile of lake water body, three zones can be identified in the lake: (1) 0–1 m: mixolimnion zone with δ18O varying from–12 to–11.1‰; (2) 1.0–3.0 m: zone with transitional properties with δ18O varying from–11.1 to–5.5‰; (3) 3.0–7.6 m: monimolimnion zone with highest values of δ18O—from–5.5 to–4.7‰.

The formation of present-day resources of surface and subsurface waters in European Russia

Variations in the characteristics of the annual, dry-season, and minimal monthly runoff in rivers of European Russia for the recent 35 years (1975–2005) have been estimated and analyzed in comparison with a period of approximately the same duration (1935–1969). The genesis of runoff for different river basins and the major causes of current changes in runoff characteristics have been studied. Regional regularities in the hydrological and geohydrological processes have been identified, and zoning of the territory has been performed with identification of specific features in the formation of river runoff in the European North and the basins of the Volga, Don, Ural, etc. The natural resources of surface and subsurface waters over 1970–2005 have been re-estimated with the construction of appropriate maps. Water availability and load on water resources have been analyzed.

Winter runoff variations in European Russia

The space and time variations of winter low-water runoff and its major characteristics are considered. The study area includes the basins of major rivers in European Russia: the Northern Dvina, the Onega, the Mezen, the Volga, and Don, etc. Variations of the minimal, mean, and maximal runoff values in winter low-water season are evaluated against the background of climate changes in recent decades. The extent of such changes over period 1978–2010 is given and compared with period 1946–1977.

EVALUATION OF GLACIER MELT CONTRIBUTION TO RUNOFF IN THE NORTH CAUCASUS ALPINE CATCHMENTS USING ISOTOPIC METHODS AND ENERGY BALANCE MODELING

Frequency and intensity of river floods rise observed in the North Caucasus during last decades is considered to be driven by recent climate change. In order to predict possible future trends in extreme hydrological events in the context of climate change, it is essential to estimate the contribution of different feed sources in complicated flow-forming processes in the alpine part of the North Caucasus. A study was carried out for the Djankuat River basin, the representative for the North Caucasus system. Simultaneous measurements of electrical conductivity, isotopic and ion balance equations, and energy balance modeling of ice and snow melt were used to evaluate the contribution of different sources and processes in the Djankuat River runoff regime formation. A forecast of possible future changes in the Djankuat glacier melting regime according to the predicted climate changes was done.

Hydrograph separation of the Dzhankuat River, North Caucasus, with the use of isotope methods

The formation of snowmelt runoff from the Dzhankuat glacier has been considered and the hydrograph of the Dzhankuat R. has been separated with the use of isotope and ionic balance. Isotope variations of runoff at the outlet section of the Dzhankuat R. have been studied for two ablation seasons of 2013 and 2014. The separation of 2014 hydrograph was based on δ18O and mineralization values obtained for various sources of Dzhankuat R. recharge: precipitation, snow of different seasons, firn, ice, and groundwater. The isotopic separation of the hydrograph has shown that, in June, a considerable portion (15–20%) of Dzhankuat R. total runoff is due to the melting snow cover that has formed during spring snowfalls. In June, the proportion of this component in the total daily runoff can reach 36%. The contribution of the runoff originating from winter-snow melting varies from 20% in the early to 50% in the late June. In August and September, the share of groundwater varies from 30 to 100%; the share of precipitation, from 0 to 30% (on the average for the period, 6%); and the share of water from melting firn and ice, from 0 to 70% (on the average, 38.6%).