Geographers have found that river floods in Europe have become more frequent and intense over the past 30 years. In Russia, the southern regions are in greatest danger, in particular, the Krasnodar and Stavropol Territories. The results of a large-scale study are published in the July issue of the journal Nature.
The study of river floods was carried out by an international team of scientists, including a professor of the Faculty of Geography of Lomonosov Moscow State University, Deputy Director of the Institute of Geography of the Russian Academy of Sciences, Andrei Panin. The scientists have compiled a database of 9576 river floods in Europe and identified nine periods of the highest flood intensity over the past 500 years: 1500-1520, 1560-1580, 1590-1640, 1630-1660, 1750-1800, 1840-1880, 1860-1900, 1910-1940, 1990-2016.
fig1.jpg
According to scientists, the last period of intense flooding is different from all previous ones. Thus, the seasonality of extreme floods has become more pronounced: in Central Europe, 55% of floods occurred in summer, while in previous periods, only 41–42% of floods occurred in the summer months. In Western Europe, winter floods have become more frequent. In Southern Europe, increased evaporation and convection have led to an increase in the number of autumn floods.
In addition, in each of the previous periods, floods occurred on different territories. For example, in 1592-1640 they manifested themselves only in the Iberian Peninsula and in the south of France; in 1860-1890 - in the east of Central Europe; and in 1910-1940 - only in Scandinavia. The period of 1990–2016 was the first in the last 500 years when floods covered all of Western and Central Europe.
fig4.jpg
It is also characteristic that in the past periods of floods coincided with intervals of cooling of the climate, but in the last three decades the frequency of floods has increased during the warming, perhaps the most significant in the last millennium.
“At the same time, 2016 may not be the end of a period rich in floods. It's just that the observational data used in the study ends that year,” says Andrei Panin.
fig3.jpg
Andrei Panin also noted that in Eastern Europe, which includes the European part of Russia, Ukraine, Belarus and the Baltic countries, no statistical analysis was carried out due to the lack of observational data.
“Throughout this former part of the Russian Empire, in area comparable to the rest of Europe, there were only six gauging stations, where the series of observations of water levels exceed 200 years. These are Volga - Nizhny Novgorod and Astrakhan, Dnepr - Dnepropetrovsk, Severnaya Dvina - Arkhangelsk, Neva - St. Petersburg and Daugava - Riga. Moreover, not all of them are suitable for analyzing flood activity. For example, floods on the Neva are caused not by rains or melting snow, but by wind surges from the Baltic. Moreover, the Neva flows from Lake Ladoga, which controls its level. The rest of the Eastern European rivers also stand apart from the rivers of Central and Eastern Europe in terms of their hydrological regime. We have cold winters, and the highest water levels are during spring floods. Floods in our country are caused by an unusually large amount of snow and a "friendly" spring, and in the northern part of the Russian Plain they are also caused by ice jams, which dam up the rivers flowing to the north. All these are phenomena that are not typical for Central and West European rivers. There, flooding is triggered by heavy downpours, sometimes coinciding with snow melting in spring, but not necessarily,” says Andrey Panin.
According to the scientists, over the past 30 years, the hydroclimatic conditions in Europe have changed. Although precipitation leading to flooding is not necessarily due to air temperature anomalies, both are governed by atmospheric circulation, the nature and extent of ocean-atmosphere interactions. However, the use of climate models suggests that the current and future increases in precipitation in Europe may be due to thermodynamics - the higher storage capacity of the heated atmosphere, rather than changes in circulation.
fig2.jpg
"For which territories of the European part of Russia are the obtained results relevant? As we said above, in the northern and central regions, floods are associated with melted snow waters. Climate warming reduces the risk of such floods, since winter becomes shorter and warmer, and less snow accumulates. And in the southern regions - in the Kuban region, in the Stavropol region and in the entirety of the North Caucasus - the response of hydrological systems to climate warming follows the Central and Western European scenario, as evidenced by a series of devastating floods that have occurred in this region since the beginning of this century. Here, it is necessary to invest in flood protection measures, hydrological forecasting tools, and above all, to restore a fairly thinned network of hydrometric and meteorological observations," says Andrei Panin.