River floods Czech Republic
Czech Republic: The 2002 floods
The 2002 floods in central Europe consisted of 15 major floods affecting Austria, the Czech Republic, Germany, Slovakia, and Hungary (22). There were over 100 fatalities connected with the floods in central Europe (10). Around Europe, around 250 deaths by floods in 2002 have been reported (22).
The economic loss by the 2002 floods in central Europeis estimated at 9 billion Euros for Germany (German government’s estimate), 3 billion Euros for Austria, and 2.5 billion Euros for the Czech Republic (estimates from (24)). The event thus replaced the European winter storm Lothar of December 1999 as the most expensive weather-related catastrophe in Europe in recent decades (23).
As of December 2002, total economic damage estimates exceeded 15 billion Euro, of which about 15% is insured. Germany was the hardest hit, with over two-thirds of the flood’s total losses. In particular, the state of Saxony (capital Dresden) sustained nearly half the total loss. The largest loss after Germany was in the Czech Republic, with over 3 billion Euro in damage, of which over a third was concentrated in Prague. A primary driver of the large loss in 2002 was the flood’s costly impacts on Dresden and Prague, where massive flooding affected both residential and commercial properties (30).
Total damage in Prague is estimated at nearly 1 billion Euro. The districts of Lesser Town (Malá Strana), Old Town, the Jewish Quarter (Josefov), and Karlin suffered particularly heavy losses. Below-ground entry of water to basements caused most of the damage in the Old Town and Jewish Quarter, while overland flooding affected both the Lesser Town and Karlin. Ancient and unmapped tunnels exacerbated the problem in this historic city (30).
Less than 50% of the total loss in the Czech Republic was insured (30).
The catastrophic flooding that occurred in Austria, the Czech Republic, and Germany was the result of two periods of intense rainfall: on August 6 and 7, and on August 11 and 13.
On 6 and 7 August, there was a first large-scale rainfall event in central Europe. It affected a region encompassing the southwestern part of the Czech Republic, Lower Austria, and southeastern Germany. More than 100 mm of rain was observed at several weather stations in eastern Bavaria. In spite of the fact that these amounts have return periods of 50-100 years, they did not cause major flood waves due to the low antecedent river flows and still unsaturated soils (28). For Lower Austria, however, the local intensities and their consequences were much larger: for the River Kamp, for instance, a peak discharge was reached with an estimated return period of several thousand years (29).
On August 12, the River Danube in Austria burst its banks at several points in the provinces of Salzburg, Upper Austria, and Lower Austria, which are in northern and central parts of Austria. An estimated 10,000 houses in these areas were damaged or destroyed (30).
Although this initial phase of rain produced some localized flooding, much of the water runoff was contained by a series of reservoirs (known as the Vltava Cascade) upstream of Prague. Water was gradually released from the dams over the following days, but the increased capacity was insufficient to prevent the flood wave that followed less than a week later (30).
A second, more expansive and intense period of rain fell from August 11 and 13. It was produced by an extratropical system classified as the Genoa Cyclone Type Vb, typified by its track from the north Adriatic Sea toward Poland. Genoa Cyclones of this type commonly occur in the spring. However, two specific features of the August Genoa Cyclone led to the extraordinary amounts of rain. First, this cyclone moved more slowly than is commonly observed in the spring. Second, water temperatures in the Adriatic and Mediterranean Seas are significantly warmer in August than in the spring season. These factors caused substantial amounts of atmospheric moisture to advance north from the Adriatic Sea, fuelling the extreme rains (30,32).
Rainfall from the cyclone was focused in two areas: 1) near the Czech/German border in the Erzbirger Mountains and 2) in south Bohemia and northern Austria. The rainfall triggered flood waves in the upper portions of the Danube and Vltava catchments. One flood wave progressed down the Danube through Austria, Slovakia and Hungary, causing minor damages in the region. A more catastrophic flood wave progressed down the Vltava through Prague and down the Elbe through north Bohemia and Germany (30).
A total of 312 mm of rain within 24 hours was reported for the time period between 0600 GMT on 12 August and 0600 GMT on 13 August, the highest amount of daily precipitation ever measured in Germany (25). While rainfall was particularly extreme on the north-eastern slopes of the Erz Mountains, extraordinary amounts of precipitation were also observed further south in the western Czech Republic, southeastern Germany, and northeastern Austria. … The extreme flow rates in many tributaries of the Elbe and Danube subsequently led to major floods in both rivers (23). Unprecedented flood heights, with return periods of up to 500 years, were recorded (30).
A main contribution to the Elbe flood originated from the River Vltava, which inundated the city of Prague between 13 and 15 August. A return period of 500 years is estimated for the flood levels at Prague (26). The Elbe flood crest reached Usti in the evening of 16 August, and Dresden in the morning of the 17th. By this time the River Elbe had inundated several historical buildings in Dresden. Other parts of Dresden, such as the central railway station, were flooded by the River Weisseritz (33).
As the floodwaters approached Prague, around 50,000 residents were evacuated, all bridges across the Vltava were closed to traffic, and temporary flood barriers nearly 3 m in height were erected along the banks to protect the Old Town. The river flow peaked on August 14 and the flooding was described as the worst in over a century. Many historic buildings were flooded to the first floor, and the state emergency declaration lasted until October 31.
The combined effects of surface water and underground seepage also flooded the Metro, Prague’s primary public transit system. Prague’s Metro is a modern, below-ground electric mass transit system. Flooding closed thirteen stations and the associated connecting lines. Repairs continued for at least 6 months, at an estimated cost of 230 million Euro. Five stations flooded as water poured in from the street. Water leaked into others through poorly sealed electrical cables, which extend through stations and tunnels up to the surface (30).
The flood wave continued to travel downstream toward the German border and into the River Labe, severely damaging several towns and villages. Across the Czech Republic, 17 people died and some 220,000 people were evacuated. As the flood moved downstream, towns were generally flooded for longer periods of time (30).
In Dresden, about 200 km (124 miles) from Prague, the River Weisseritz (a tributary of the Elbe which flows from the south near the Czech border) initially broke its banks on August 12. Subsequent flooding submerged the main railway station and parts of the historic city center. Water inundated low-lying suburbs along the river, as well as basements and ground floors of several important historic buildings in the city’s center. Fortunately, flood warnings allowed many original paintings and treasures to be removed from the lower levels of these buildings (30). In Dresden, five hospitals, with a total of >5,000 beds, were evacuated when they were surrounded by water (31).
On the morning of August 17, the river level in Dresden peaked at a record height of 9.4 m, superseding the previous record of 8.8 m set in 1845. The increase in river height in Dresden was more gradual and of greater magnitude than the flood peak in Prague. The 160-km progression of the flood wave from Prague to Dresden spanned three days. In total, the flood wave took around 12 days to travel from the upper reaches of the Vltava to the mouth of the Elbe in northern Germany, a distance of over 1,000 km (30).
Across the affected region of Germany, 180 bridges were damaged, along with 740 km of roads and 538 km of railway track. The main railway line between Dresden and Prague was closed for more than four months. In the immediate aftermath of the floods, the German Government pledged to reduce construction on floodplains and limit the straightening of river channels (30).
Czech Republic: Vulnerabilities - Non-climatic causes
The August 2002 floods, just like the earlier floods along the River Oder in 1997, the Rhine in 1995 and severe flooding in 1993, highlighted many of the same issues. Recent and planned developments on floodplains, river channel straightening, and a general under-investment in flood defenses have all contributed to the increasing flood risk. Without much private flood insurance in central Europe, governments frequently carry the burden of damage (30).
There is no evidence from flood observations over the last 80-150 years for recent upward trends in the occurrence rate of the extreme floods (return periods of 100 yr and more) that occurred in central Europe in July 1997 (Oder) and August 2002 (Elbe) (36). In fact, over this period a decrease in winter flood occurrence in both rivers has been found, while summer floods show no trend (36). The reduction in winter flood occurrence for these rivers can partly be attributed to fewer events of strong freezing; following such events, breaking river ice at the end of the winter may function as a water barrier and enhance floods severely. In both rivers, the last ice flood occurred in 1947 (36). Reduced freezing may have been caused by warming (37) or increased pollution of river waters. Elevated winter temperatures could also have had an effect via a reduction of occurrence of frozen soil, which has low absorbing capacity (38).
Contaminated and toxic waters
Many Eastern European cities that are prone to floods are in close proximity to industrial areas, mining operations, or are host to brownfield sites. As a result, people and settlements in the region run a significant risk to be exposed to contaminated and toxic waters. For instance, in 2000, a flood in Romania (Baia Mare) resulted in the breach of a tailings pond and of cyanide-laced waste from a gold mining operation being wasted into the Tiza and Danube Rivers. The accident not only affected the ecosystems of these rivers, but the drinking water of approximately two million people in Hungary. Similarly, flooding of a chemical plant in the Czech Republic in 2002 resulted in chlorine and other chemicals being washed into the Elbe and the deposition of dioxins on the shores of the River (39).
Czech Republic: Vulnerabilities - Future flood risk
Between 1998 and 2002 Europe suffered over 100 major damaging floods, including the catastrophic floods along the Danube and Elbe rivers in 2002. Since 1998, floods have caused some 700 fatalities in Europe, the displacement of about half a million people and at least 25 billion Euros in insured economic losses. The floods in central Europe cannot be regarded as caused by climate change, but the probability of flooding is estimated to increase as a result of climate change. Weather conditions indicate phenomena that, in accordance with present understanding, would be caused by climate change (31).
Studies on small-forested catchments showed that annual runoff is projected to decline in 2071–2100 compared to 1967–1990 by 10 to 30%. Impacts on the distribution of monthly flow are projected to be significant, with summer– autumn decreases of 30 to 95%, and winter increases of up to ~40%. Mean daily flows are estimated to decrease by ~70% from August to November. These results are based on 2 general circulation models, downscaled using 3 regional climate models under the A2 and B2 emission scenarios, in combination with a hydrological model (42). The projected changes in runoff are due to seasonal redistribution of precipitation with expected summer decreases and winter increases, and evapotranspiration increase in the summer as a result of higher temperature and prolongation of the growing season (42).
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 (41).
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 (41).
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 (34).
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 (35).
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 (35).
Adaptation strategies - Infrastructure
The most important measure from the standpoint of flood protection is the Prevention of Floods programme of the Ministry of Agriculture (Government Resolution No. 382/2000), which is intended to improve protection of the most endangered areas against floods. A higher degree of protection can be achieved through measures of investment and non-investment character (construction and renewal of polders, reservoirs and dykes, increasing the flow capacity of the channels of water courses, delimitation of inundation zones, analysis of outflow conditions and delimitation of the extent of the territory endangered by floods) (33).
Adaptation strategies - Nature restoration
The River System Restoration Programme (Ministry of the Environment Directive No. 5/2006) is intended to create conditions for the renewal of the natural environment and sources exploited by humans and to consistently increase the water retention ability of the landscape. It contributes to mitigation of the negative impacts of climate change through renewal of the natural function of water courses, including dead arms and spring areas, renewal of floodplains and bank vegetation, establishment and restoration of elements of the system of ecological stability bound to the water regime, elimination of lateral obstacles on water courses, renewal of the retention ability of the landscape (construction of fishponds, polders, etc.) and renewal of the natural function of water courses (33).
Adaptation strategies - Emergency preparedness
There are lessons to be learned from the 2002 floods for a.o. emergency preparedness. Both in the Czech Republic and in Germany, hospitals were affected by the floods.
In Dresden, five hospitals, with a total of >5,000 beds, were evacuated when they were surrounded by water. At the flooded hospitals, many of the electrical services and computer server facilities were installed in underground ducts. It is questionable whether it is beneficial and cost-effective to install sensitive technical equipment underground when there is a risk of flooding. Emergency equipment should be placed at a relatively high level in the building (31).
In the Czech Republic, the floods caused power outages, making it difficult or impossible to inform and communicate with staff and patients in the affected hospitals. Communication equipment that works without electricity and reaches both staff and patients in all hospital wards must be installed. As a result of the floods, many computerized case record systems were non-functional. Secure patient reports should be backed-up on computer servers outside of the hospitals. This source must be capable of quickly supplying hard copies (31).
There is also much to be learned from the German Defense Forces’ air support capability for the large-scale evacuation of severely ill patients over long distances. In the future, the procedure for the long-distance transportation of a large number of severely ill or injured people should be clarified in national plans. The plans must be able to be implemented on short notice. Coordination and management of a large-scale evacuation must be clarified and practiced. Helicopters for short-distance transportation and planes for long-distance transportation are the best ways to evacuate patients from hospitals. Hospitals should have helipads above possible flood levels (31).
Adaptation strategies - Contaminated and toxic waters
Development of cities should be prevented in areas that are vulnerable to toxins, contaminants, or other health hazards that may arise as a consequence of the flooding of industrial and mining operations or brownfield sites. At the same time, concerted efforts need to be made to relocate existing industrial plants out of floodplains and to remediate brownfield sites (40).
Adaptation strategies - EU Directive on flood risk management
The new EU Directive on flood risk management, which entered into force in November 2006, introduces new instruments to manage risks from flooding, and is thus highly relevant in the context of adaptation to climate change impacts. The Directive introduces a three-step approach (2):
- Member States have to undertake a preliminary assessment of flood risk in river basins and coastal zones.
- Where significant risk is identified, flood hazard maps and flood risk maps have to be developed.
- Flood risk management plans must be developed for these zones. These plans have to include measures that will reduce the potential adverse consequences of flooding for human health, the environment cultural heritage and economic activity, and they should focus on prevention, protection and preparedness.
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for the Czech Republic.
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