River floods Russia
Russia: Vulnerabilities – Floods in the past
The total area of potentially flood-affected territory in Russia is determined to be 400,000 km2, from which about 50,000 km2 are flooded annually. These include more than 746 settlements (including 40 big cities) with more than 4.6 million inhabitants potentially facing floods (45). Owing to geographical features of the Russian territory, approximately half of the floods are caused by snow and ice melt, rain-induced floods and ice jam floods account for 36 and 15 %, respectively, while a few number of coastal floods are triggered by wind surges (46). Flood events account for only 10 % and droughts for 4 % of all hydrometeorological hazards in Russia in the period 1991-2015. However, these two hazards amount for more than 40 % of economic loss in total (47). Although the number of hydrometeorological hazards and floods has an increasing tendency, the share of floods to the total number has an overall decreasing tendency (44).
Many cities and regions of Russia are partially flooded once within 8–12 years. At the moment the densely inhabited regions of the North Caucuses and the Don River basin (i.e., Krasnodar territory and Stavropol territory, Rostov, Astrakhan and Volgograd regions) are flooded once within 5 years (25).
In Russia floods, storms, typhoons and hurricanes annually kill up to 1000 people while the total number of people with traumas and post-traumatic shocks has not been calculated yet. … In spring and summer 2001 one of the earth’s largest floods occurred in Lensk (Sakha Republic). The total damage was assessed at more than 7 trillion roubles (25).
Observations of past data on flooding suggest that there is an increase in frequency of large flood events. The incidence of great floods (floods that exceed 100-year levels in basins larger than 200,000 km2) has increased substantially in the 20th century, giving a statistically significant positive trend in risk of great floods. Modeling analysis also indicate that the 100-year flood was exceeded more frequently as a result of a quadrupling in CO2 levels and with particularly strong increases in frequency projected in northern Asia (22).
Another study shows that the frequency and intensity of runoff-derived floods (mostly snowmelt in the Russian territory) in European Russia’s river mouths have shown a substantial decrease since the mid-twentieth century and especially during the 2000s (44). In Russia, heavy rain events are playing a more important role in flood hazards generation (48). These tendencies can be explained by changes in the water regime of Russian rivers in which the cold-period discharge characteristics are being transformed (49). The rising number of extreme heavy rainfall events is a sign of such a transformation, and it can be shown that rain-driven floods events will become more common, whereas snowmelt-driven floods are decreasing especially in small- and mid- sized rivers with a drainage area < 50,000 km2 (44).
The annual runoff increased by 15-40% for the period 1978-2005 relative to 1946–1977 at rivers in the western regions of the European part of Russia and tributaries on the left bank of the Volga River. The runoff increased by 10-15% in the upper basin of the Northern Dvina, upper reaches of the Dnieper, and left-bank tributaries of the Don. A runoff increase of 20-40% also took place on the left-bank tributaries of the Tobol and the Irtysh rivers in the Asian part of Russia. Runoff increases were also observed in the Yenisey basin (8%) and in the greater part of the Lena basin, particularly in the last decade of the 20th century. The runoff also increased by 5-15% in the north-eastern river basins of the Asian part of Russia (21).
An increase in flooding events in the first decade of the 21st century has been reported for several Russian river basins, including the Volga and Ob (32). At the beginning of the 21st century, in many economic regions of Russia, the frequency of catastrophic flooding caused by high water and spring floods increased by 15% vs. values of the last decade of the 20th century. Storm surges in Neva River in St. Petersburg have become more frequent (21). In the past five years, the Lena, one of the world’s 10 largest rivers, has experienced two floods more severe than any previous recorded flood (28). Others report a decrease of the number of observed runoff floods during the period 1991-2015, and related this to major rivers runoff regulations (Don, Kuban, Volga and Terek), the construction of flood protection measure (Severnaya Dvina). Additionally, and a large number of reservoirs constructed in European Russia since the 1950s (44).
The impact of climate change on flood risk in major Russian river basins is highly complex. Generally an increase of annual discharge has been found but some seasonal factors tend to mitigate against an increase in flood risk, with river flow rates likely to increase during winter and spring but decrease in summer, caused by higher temperatures which reduce snow-cover and permafrost coverage. However, there is no clear consensus on the seasonality of flood risk. Earlier melt onset causing ice break-up has not found to be occurring earlier and ice damming of rivers is a significant factor in flood risk (24).
A factor that may affect the numbers of hazardous events is the higher level of information technology. For example, in Russia during the Soviet period or in the early 1990 it was necessary to collect information about hazardous events from newspapers or inform local reports of the Hydrometeorological Service. Nowadays, information about flood events is publicly available in the social media and it takes a few hours (sometimes only minutes) to know that a flood took place (44).
Russia: Vulnerabilities – Dangerous ice dams in lowland rivers
In lowland rivers of European Russia ice jams (and dams) can lead to floods. Congestion of ice or sludge in channels results in a sharp rise in water level, and often leads to flooding. On large Russian rivers flowing from south to north (the Northern Dvina, the Pechora, the Ob, the Yenisei, the Lena and others), ice jam stages during spring ice run are often higher than the maximum water levels during flooding. Information on the ice regime of the rivers of European Russia was summarized from observations at 300 hydrological stations in the period from 1936 to 2013. This information includes the appearance of ice, freeze-up, breakup, beginning of the spring ice run and ice clearance, the duration of ice cover, autumn sludge run and spring ice run, typical water levels during spring ice run and ice jam formation, and the frequency of ice jams (41).
The danger of ice on Russian rivers
Ice jam floods are particularly dangerous because they are accompanied by an ejection of ice on the shore that breaks structures (dam slopes, levees, bridge pillars) located within the flood zone. The damage caused by ice jams typically far exceeds the damage caused by floods in the ice-free period. In addition to flooding and damaged hydraulic structures, prolonged ice jam delays the cleaning of the river of ice, reducing the navigation period. Rises of water level below hydroelectric dams caused by ice and sludge jams result in a reduction of power production (42).
Current changes in ice regime
The distribution of ice jams along the river not only depends on temperature. It also depends on water discharge during breakup. Along with higher temperatures the water regime of rivers changes: in winter and autumn precipitation more often falls as rain instead of snow. Loss of snow accumulation in winter results in a reduction of flood discharge and flood levels, an earlier start of spring floods, and less power to move the ice. Powerful flood waves push the ice over a greater distance, and ice jams are formed further downstream than in years with low water discharge (43).
The majority of European Russian rivers freeze for 4 months or more each year. Over the last decades (since the period of 1961-1990) ice regime changes due to climate change and other impacts have been quite small: the dates of breakups on the rivers in the north of European Russia have shifted earlier by no more than 5 days, and changes in the maximum thickness of ice do not exceed 10 cm. However, climate change now causes simultaneous breakups in quite extensive sections of the rivers. This enhances the ice jam danger. In addition, low water during spring breakup contributes to stable multi-day ice jams. Total ice run duration on the Volga, for instances, increases sharply and can reach 40 days, instead of the average of 5 days in previous decades. The absence of steady freeze-up, and prolonged thaws that split the period with ice phenomena into two or more separate parts are the most significant changes in the ice regime of rivers within European Russia (41).
Less predictable in the short-term, lower risk in the long term
The ice regime changes in a complicated way. On the one hand, higher temperatures affect the period of freezing, the process of thawing and the formation of ice dams. On the other, the water regime of rivers changes: winter and autumn precipitation more often falls as rain instead of snow, leading to less snow accumulation in the winter and lower river discharge in spring. The latter means flood waves have less power to push the ice over a greater distance. Due to this combination of effects the hazard of ice jamming is less predictable in the short term. In the long term, however, climate change leads to a significant reduction of the duration of the ice regime periods, and a lower risk of ice jamming (41).
Russia: Vulnerabilities – Floods in the future
Projections on future changes in flood frequency in European Russia are not univocal:
- Climate model integrations suggest increases in the frequency and intensity of heavy rainfall in high latitudes of the northern hemisphere (23), thereby increasing flood hazard. In the 21st century, the number of floods will probably increase on rivers of a significant part of Russia. As a result of expected precipitation increase, the probability of flooding caused by rainfall at small and medium rivers of the European part of Russia, in particular, of the North Caucasus, and of the Far East will increase. The probability of storm surges will increase in deltas of big rivers running into the Azov and Baltic seas (21).
- In European Russia and West Siberia a widespread increase in future return period of large flood events was estimated. The return period of the 100-year flood level in the Volga and the Dniepr rivers, for instance, is projected to increase to 671 years and over 2000 years, respectively, suggesting a strong decrease in flood hazard (33). For Northern European Russia, a general decrease in the 100-year flood level with climate change was found of 20-40% towards the end of the 21st century (34).
Maximal (spring) river runoff depends on the rate and mass of snow thawing, accumulated in winter. Model simulations show a decrease of runoff maximum and its earlier occurrence at the Don, Volga and Ural watersheds in the 21st century. It is related to diminishing snow mass in winter (26,35). The runoff of northern rivers, including Pechora, Severnaya Dvina and Ob, increases significantly by the middle of the 21st century due to faster snow thawing, notwithstanding some decrease of the snow mass by the start of spring (26). According to an ensemble of models the average river runoff of the Ob river and Lena river grows by more than 10% and 20%, respectively, in the 21st century at a moderate scenario of climate change (26).
An increase in high and low flow volumes was shown for the Lena River in the period 2070-2099 compared with the reference period 1981-2010, in an assessment based on five climate (GCMs) and five hydrological models, and four different scenarios of climate change ranging from a low- to a high-end scenario of global warming (the so-called RCPs 2.6, 4.5, 6.0 and 8.5) (37). Lena’s flow regime is strongly influenced by the accumulation and melting of snow and ice, and flows therefore are strongly influenced by the rise of temperature. Model projections indicate that high flow volumes (the 10% highest discharges) will increase for the Lena River up to 40% in 2100. A similar trend was shown in other studies (38,40). For the Lena advancing of the snowmelt season and an earlier beginning of the flood season is projected (40). An increase of low flow volumes was projected for Lena due to more snowmelt. Similar changes to low flows in the Lena River were shown in previous studies (39).
A reduction of winter ice levels is likely to reduce flood risk in spring. Flood risk in winter itself may increase due to possible rapid snowmelt from rain-on-snow events or warm periods in middle of winter. In summer, reduced precipitation will lead to a reduction in flood risk, but the possibility of extreme precipitation events exists causing localised flood events (24).
In the Arctic, increased water discharges occurring earlier in the spring may be blocked by ice jams, causing the duration of inundated flood plains to increase from the current (2009) 12 days to 24 days in 2030. Ice-jam-induced floods in the Lena River Basin are expected to double by 2015 (27). In St. Petersburg, the probability of a disastrous flood is expected to increase in the next 5-10 years (with respect to 2009, red.) (27).
Europe: casualties in the past
The annual number of reported flood disasters in Europe increased considerably in 1973-2002 (1). A disaster was defined here as causing the death of at least ten people, or affecting seriously at least 100 people, or requiring immediate emergency assistance. The total number of reported victims was 2626 during the whole period, the most deadly floods occurred in Spain in 1973 (272 victims), in Italy in 1998 (147 victims) and in Russia in 1993 (125 victims) (2).
Throughout the 20th century as a whole flood-related deaths have been either stable or decreasing while economic burdens of flooding and related societal disruptions have become decidedly worse. 20th century flood disaster death tolls have been typically averaging fewer than 250 per year (3).
Europe: flood losses in the past
The reported damages also increased. Three countries had damages in excess of €10 billion (Italy, Spain, Germany), three in excess of 5 billion (United Kingdom, Poland, France) (2).
Expressed in 2006 US$ normalised values, total flood losses over the 1970–2006 period amounted to 140 billion, with an average annual flood loss of 3.8 billion (4). Results show no detectable sign of human-induced climate change in normalised flood losses in Europe. There is evidence that societal change and economic development are the principal factors responsible for the increasing losses from natural disasters to date (5).
Policy makers should not expect an unequivocal answer to questions concerning the linkage between flood-disaster losses and anthropogenic climate change, as this field will very likely remain an important area of research for years to come. Longer time-series of losses are necessary for more conclusive results (6).
Europe: flood frequency trends in the past
In 2012 the IPCC concluded that there is limited to medium evidence available to assess climate-driven observed changes in the magnitude and frequency of floods at a regional scale because the available instrumental records of floods at gauge stations are limited in space and time, and because of confounding effects of changes in land use and engineering. Furthermore, there is low agreement in this evidence, and thus overall low confidence at the global scale regarding even the sign of these changes. There is low confidence (due to limited evidence) that anthropogenic climate change has affected the magnitude or frequency of floods, though it has detectably influenced several components of the hydrological cycle such as precipitation and snowmelt (medium confidence to high confidence), which may impact flood trends (36).
Despite the considerable rise in the number of reported major flood events and economic losses caused by floods in Europe over recent decades, no significant general climate‑related trend in extreme high river flows that induce floods has yet been detected (7).
Hydrological data series do not indicate clear upward trends in the frequency and magnitude of floods in Europe. The direct anthropogenic causes include land use change, river channel modifications and increased activities in areas vulnerable to floods. Thousands of square kilometres of impermeable surfaces have been created, coastal urbanization has been extensive. The overall impact of these changes probably exceeds the impact of trends in meteorological variables in today's Europe (8).
In western and central Europe, annual and monthly mean river flow series appear to have been stationary over the 20th century (9). In mountainous regions of central Europe, however, the main identified trends are an increase in annual river flow due to increases in winter, spring and autumn river flow. In southern parts of Europe, a slightly decreasing trend in annual river flow has been observed (10).
In the Nordic countries, snowmelt floods have occurred earlier because of warmer winters (11). In Portugal, changed precipitation patterns have resulted in larger and more frequent floods during autumn but a decline in the number of floods in winter and spring (12). Comparisons of historic climate variability with flood records suggest, however, that many of the changes observed in recent decades could have resulted from natural climatic variation. Changes in the terrestrial system, such as urbanisation, deforestation, loss of natural floodplain storage, as well as river and flood management have also strongly affected flood occurrence (13).
Europe: projections for the future
In 2012 the IPCC concluded that considerable uncertainty remains in the projections of flood changes, especially regarding their magnitude and frequency. They concluded, therefore, that there is low confidence (due to limited evidence) in future changes in flood magnitude and frequency derived from river discharge simulations. Projected precipitation and temperature changes imply possible changes in floods, although overall there is low confidence in projections of changes in fluvial floods. Confidence is low due to limited evidence and because the causes of regional changes are complex, although there are exceptions to this statement. There is medium confidence (based on physical reasoning) that projected increases in heavy rainfall would contribute to increases in rain-generated local flooding, in some catchments or regions. Earlier spring peak flows in snowmelt- and glacier-fed rivers are very likely, but there is low confidence in their projected magnitude (36).
More frequent flash floods
Although there is as yet no proof that the extreme flood events of recent years are a direct consequence of climate change, they may give an indication of what can be expected: the frequency and intensity of floods in large parts of Europe is projected to increase (14). In particular, flash and urban floods, triggered by local intense precipitation events, are likely to be more frequent throughout Europe (15).
More frequent floods in the winter
Flood hazard will also probably increase during wetter and warmer winters, with more frequent rain and less frequent snow (16). Even in regions where mean river flows will drop significantly, as in the Iberian Peninsula, the projected increase in precipitation intensity and variability may cause more floods.
Reduction spring snowmelt floods
In snow‑dominated regions such as the Alps, the Carpathian Mountains and northern parts of Europe, spring snowmelt floods are projected to decrease due to a shorter snow season and less snow accumulation in warmer winters (17). Earlier snowmelt and reduced summer precipitation will reduce river flows in summer (18), when demand is typically highest.
For the period 2071-2100 the general feature is a decrease of extreme flows in areas where snowmelt floods are dominating in the present climate. The hundred year floods will attenuate by 10-50% in northern Russia, Finland and most mountainous catchments throughout Europe. An increase by similar amount is projected in large areas elsewhere, whereas a mixed pattern is likely in Sweden, Germany and the Iberian Peninsula (2).
Increase flood losses
Losses from river flood disasters in Europe have worsened in recent years and climate change is expected to exacerbate this trend. The PESETA study, for example, estimates that by the 2080s, some 250-400 million Europeans could be affected each year (compared with 200 million in the period between 1961 and 1990). At the same time, annual losses due to river flooding in Europe could rise to €8-15 billion by the end of the century compared with an average of €6 billion today (29).
Large differences across Europe
Annual river flow is projected to decrease in southern and south-eastern Europe and increase in northern and north-eastern Europe (19).
Strong changes are also projected in the seasonality of river flows, with large differences across Europe. Winter and spring river flows are projected to increase in most parts of Europe, except for the most southern and south-eastern regions. In summer and autumn, river flows are projected to decrease in most of Europe, except for northern and north-eastern regions where autumn flows are projected to increase (20). Predicted reductions in summer flow are greatest for southern and south-eastern Europe, in line with the predicted increase in the frequency and severity of drought in this region.
Climate-related changes in flood frequency are complex and dependent on the flood generating mechanism (e.g. heavy rainfall vs spring snowmelt), affected in different ways by climate change. Hence, in the regions where floods can be caused by several possible mechanisms, the net effect of climate change on flood risk is not trivial and a general and ubiquitously valid, flat-rate statement on change in flood risk cannot be made (30).
Flood risk tends to increase over many areas owing to a range of climatic and non-climatic impacts, whose relative importance is site-specific. Flood risk is controlled by a number of non-climatic factors, such as changes in economic and social systems, and in terrestrial systems (hydrological systems and ecosystems). Land-use changes, which induce land-cover changes, control the rainfall-runoff relations in the drainage basin. Deforestation, urbanization and reduction of wetlands diminish the available water-storage capacity and increase the runoff coefficient, leading to growth in the flow amplitude and reduction of the time-to-peak. Furthermore, in many regions, people have been encroaching into, and developing, flood-prone areas, thereby increasing the damage potential. Important factors of relevance to flood risk are population and economy growth, flood protection strategy, flood risk awareness (or flood risk ignorance) behaviour and a compensation culture (30).
Adaptation strategies - General
Non-structural measures are in better agreement with the spirit of sustainable development than structural measures, being more reversible, commonly acceptable, and environment-friendly. Among such measures are source control (watershed/landscape structure management), laws and regulations (including zoning), economic instruments, an efficient flood forecast-warning system, a system of flood risk assessment, awareness raising, flood-related data bases, etc. As flood safety cannot be reached in most vulnerable areas with the help of structural means only, further flood risk reduction via non-structural measures is usually indispensable, and a site-specific mix of structural and non-structural measures seems to be a proper solution. As uncertainty in the assessment of climate change impacts is high, flexibility of adaptation strategies is particularly advantageous (31).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Russia.
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