M. B. Kireeva

Changing climate shifts timing of European floods

Flooding along the river Will a warming climate affect river floods? The prevailing sentiment is yes, but a consistent signal in flood magnitudes has not been found. Blöschl et al. analyzed the timing of river floods in Europe over the past 50 years and found clear patterns of changes in flood timing that can be ascribed to climate effects (see the Perspective by Slater and Wilby). These variations include earlier spring snowmelt floods in northeastern Europe, later winter floods around the North Sea and parts of the Mediterranean coast owing to delayed winter storms, and earlier winter floods in western Europe caused by earlier soil moisture maxima. Science, this issue p. 588 see also p. 552 Climate change is affecting the timing of river flooding across Europe. A warming climate is expected to have an impact on the magnitude and timing of river floods; however, no consistent large-scale climate change signal in observed flood magnitudes has been identified so far. We analyzed the timing of river floods in Europe over the past five decades, using a pan-European database from 4262 observational hydrometric stations, and found clear patterns of change in flood timing. Warmer temperatures have led to earlier spring snowmelt floods throughout northeastern Europe; delayed winter storms associated with polar warming have led to later winter floods around the North Sea and some sectors of the Mediterranean coast; and earlier soil moisture maxima have led to earlier winter floods in western Europe. Our results highlight the existence of a clear climate signal in flood observations at the continental scale.

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.

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.

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.

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.

Using isotope methods to study alpine headwater regions in the Northern Caucasus and Tien Shan

High mountain areas provide water resources for a large share of the world’s population. The ongoing deglaciation of these areas is resulting in great instability of mountainous headwater regions, which could significantly affect water supply and intensify dangerous hydrological processes.The hydrological processes in mountains are still poorly understood due to the complexity of the natural conditions, great spatial variation and a lack of observation. A knowledge of flow-forming processes in alpine areas is essential to predict future possible trends in hydrological conditions and to calculate river runoff characteristics. The goal of this study is to gain detailed field data on various components of natural hydrological processes in the alpine areas of the North Caucasus and Central Tien Shan, and to investigate the possibility that the isotopic method can reveal important regularities of river flow formation in these regions. The study is based on field observations in representative alpine river basins in the North Caucasus (the Dzhankuat river basin) and the Central Tien Shan (the Chon-Kyzyl-Suu river basin) during 2013–2015. A mixing-model approach was used to conduct river hydrograph separation. Isotope methods were used to estimate the contribution of different nourishment sources in total runoff and its regime. d18О, dD and mineralization were used as indicators. Two equation systems for the study sites were derived: in terms of water routing and runoff genesis. The Dzhankuat and Chon-Kyzyl-Suu river hydrographs were separated into 4 components: liquid precipitation/meltwaters, surface routed/subsurface routed waters.

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%).

LOW FLOW ON THE RIVERS OF THE EUROPEAN PART OF RUSSIA AND ITS HAZARDS

This paper reviews the changes in river flow of the European part of Russia during the low-flow period, characterizing groundwater flow feeding. River flow oscillations were analyzed for winter and summer periods. Statistical analyses of average low flow and the minimum monthly summer and winter discharges for 1946–1977 and 1978–2010 showed significant positive trends for all parameters of low-water period. The greatest increase is observed in the Middle Volga, where low flow has almost doubled. The low flow discharges increased by up to 50–70 % in the center of the European part of Russia and the Upper Don and its tributaries, ranging from 0 to 30 % for the northern rivers. Despite the low flow increase, the lack of water in 2010 and 2014 caused economic damage. It is shown that the observed hydrological hazards occur as a result of snow melt draughts and water management instability.

RECENT TRENDS Of RIVER RUNOff IN THE NORTH CAUCASUS

Based on observational data from 70 hydrological stations in the North Caucasus an evaluation of present values of mean annual runoff, minimum monthly winter and summer runoff was carried out. Series of maps was drawn. Significant changes in mean annual. minimum monthly and maximum runoff during last decades have been revealed in the North Caucasus. A rise in both amount of water availability and potential natural hazard is characteristic of the most of the North Caucasus that is considered to be caused by recent climate change. Mean annual runoff during 1978-2010 increased compared to 1945-1977 by 5-30 % in the foothills and by 30-70% in the plain area. An increase in winter minimum monthly runoff is as well most intensive in the plain part of study area (>100%). Within the foothills it amounts to 50-100%. In mountainous area long-term oscillation of winter minimum monthly discharge strongly depends on local factors, such as geological structure. The rate of the increase in summer minimum monthly discharge regularly grows from central foothill part of Northern Caucasus (30-50%) to the Western plain territory (70-100%). In Kuban river basin 30% of analyzed gauging stations show positive trend in maximum instantaneous discharge, while 9% negative. On the contrary, in the Eastern part – Terek river basin – negative trend in maximum instantaneous discharge is prevalent: 38% of gauging stations. Positive trend in Terek river basin is characteristic of 9.5% of analyzed gauging stations.

Djankuat Glacier Station in the North Caucasus, Russia: A Database of complex glaciological, hydrological, meteorological observations and stable isotopes sampling results during 2007-2017

The study presents a dataset on long-term complex glaciological, hydrological, meteorological observations and isotopes sampling in an extremely underreported alpine zone of the North Caucasus. The Djankuat research basin is of 9.1 km2, situated on elevations between 2500 – 4000 m, and covered with glaciers by 30%. The largest in the basin, the Djankuat 20 glacier, was chosen as representative of the central North Caucasus during the International Hydrological Decade and is one of 30 ‘reference’ glaciers in the world which have annual mass balance series longer than 50 years (Zemp et al., 2009). The dataset reported here covers 2007–2017 and contains the result of yearly measurements of snow depth and density; dynamics of snow and ice melting; measurements of water runoff, conductivity, turbidity, temperature, δ18O, δD at the main gauging station (844 samples in sum) with a one-hour or several-hours’ time step depending on the parameter; data on δ18O and δ2H 25 sampling of liquid precipitation, snow, ice, firn, groundwater in different parts of the watershed taken regularly in time during melting season (485 samples in sum); precipitation amount, air temperature, relative humidity, shortwave incoming and reflected radiation, longwave downward and upward radiation, atmospheric pressure, wind speed and direction – measured at several automatic weather stations within the basin with 15 min to one-hour step; gradient meteorological measurements to estimate turbulent fluxes of heat and moisture, measuring three components of wind speed at a frequency of 10 hertz to estimate 30 the impulse of turbulent fluxes of sensible and latent heat over the glacier surface by the eddy covariance method. All the observations were done during the ablation period (June–September) and were interrupted in winter. The dataset was published on knb.ecoinformatics.org long-term repository (doi:10.1594/PANGAEA.894807) and will be further updated. The dataset can be useful for developing and verifying hydrological, glaciological and meteorological models for high elevation territories,