Poland: Vulnerabilities - Past flood probability

Documentary data for both the Elbe and Oder have been studied to provide reliable information on heavy floods at least since A.D. 1500. These data are a combination of historical and (more recent) instrumental data. For both rivers significant downward trends in winter flood occurrence during the 20th century were shown, whereas no significant trends in summer flood risk in the 20th century could be established (21,23). The observed trends in flood risk:

• are robust against uncertainties in the stage-runoff relations (instrumental period);
• are robust against choice of runoff thresholds used to define a flood event (instrumental period);
• show negligible influences of deforestation and agricultural land use changes (historical and instrumental periods);
• (in the case of heavy floods) are insensitive to construction of reservoirs (instrumental period);
• show minimal influences of other type of river engineering work such as length reductions (historical period);
• show significant correlations with fields of atmospheric pressure variables, reinforcing the role of the cyclone’s pathway Zugstrasse Vb;
• show coherent climatic signals in the form of a reduced winter flood risk (fewer ‘‘ice floods’’) during the instrumental period as a response to regional warming.

In the case of winter floods, regional warming during the 20th century has likely reduced winter flood risk via a reduced rate of strong river freezing and related ice jam (breaking ice at the end of winter may function as a water barrier and enhance a high water stage severely) (22).in both rivers Elbe and Oder, the last ice flood occurred in 1947 (23). Reduced freezing may have been caused by warming 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 (23).

The North Atlantic Oscillation (NAO) index, an indicator of the strength of westerly airflow to Europe, yielded no significant correlation with winter flood events of Elbe and Oder. This shows that central European winter floods were not connected with warm, wet winters in western Europe (21).

Although extreme floods with return periods of 100 year and more occurred in central Europe in July 1997 (Oder) and August 2002 (Elbe), there is no evidence from the observations for recent upward trends in their occurrence rate (23).

Poland: Vulnerabilities - Present Oder flood protection

The Oder is the second largest river in Poland, after the Vistula (Wisla), both in regard to its length of 854 km, and the area of its drainage basin, 118,861 km2, of which 742 km and 106,056 km2 respectively are in Poland (24).

There have been numerous floods in historic times along the Oder, both summer rain-caused floods and winter floods, and consequently, a need has arisen for an adequate flood protection system. It consists of embankments, weirs, reservoirs (including dry flood protection reservoirs) and relief channels for the Oder and its tributaries, and a system of polders (24).

The flood of the summer of 1997 covered not only the drainage basin of the River Oder, but also that of the largest Polish river, the Vistula. However, the losses recorded in the drainage basin of the Vistula were significantly lower than those in the drainage basin of the Oder (24).

Poland: Vulnerabilities - Present flood preparedness

For several years before 1997, only minor floods had occurred in Poland. This had considerably weakened the awareness and preparedness of the nation. In 1989, a time of dramatic changes to the political and economic system in Poland began. The country entered a period of transition from the rule of a communist party and centrally planned economy towards democracy and a market economy. Under such circumstances, and in the long-term absence of really disastrous floods, the expenditure on flood protection and flood preparedness was low and kept decreasing. Flood vulnerability and hazard were not being considered seriously by decision makers, political elites and the general public (24).

Poland: The Great Flood of 1997

The Great Flood of 1997 was the greatest flood on record in Poland, both in hydrological terms (peak stage, flow, inundated area in the drainage basin of the Oder) and in economic terms (material losses). It was the effect of exceptionally intensive precipitation covering a large area. This very rare hydrological event was superimposed on the complex, changing, socio-economic system of a country-in-transition. The event was labelled as "the largest natural disaster in the 1000-year history of Poland" (24).

In the second half of June 1997, precipitation filled much of the natural available water retention, saturating available soil storage. The abundant precipitation from 4 to 10 July was caused by quasi-stationary atmospheric conditions with a front dividing humid air masses that significantly differed in temperature: hot and very water-rich air to the east, and humid and cooler polar sea air to the west. The two weather systems met over the Czech Republic and the southwest of Poland, covering the catchment area of the upper Oder and its tributaries, and stayed there for a long time, releasing large volumes of intensive precipitation, culminating between 6 and 8 July. The heavy and long-lasting rains in the period 4-10 July caused destructive flooding. Yet, a few days later, from 15 to 23 July, another series of intensive rains occurred (24).

Three phases of the 1997 flood can be distinguished (24):

• First phase: The flood struck the town of Klodzko (31,000 inhabitants) located on the river Nysa Klodzka. The town was virtually ruined, with several casualties and the destruction of numerous houses.
• Second phase: Having inundated the town of Raciborz (65,000 inhabitants), the River Oder devastated further large towns located downstream, such as Opole (131,000) and Wroclaw (700,000). The flood protection system of Wroclaw was designed for a flow rate of 2400 m3/s, yet the peak flow rate in July 1997 was nearly 50% greater. About one third of the city of Wroclaw was inundated.
• Third phase: High water levels reached the border stretch of the Oder and the lower Oder. The peak flow was reduced in consequence of the upstream inundations, so one could attempt to save towns and land. The measures taken were largely successful on the Polish side, while on the German side several breaches of embankments and significant material losses were recorded. In the border stretch and the lower Oder, there was more time for preparation, heightening and strengthening of embankments.

The Great Flood of 1997 on the Oder was long lasting as the wave travelled slowly downstream. The exceedence of the historic absolute maximum water level lasted several days. The Great Flood of 1997 had two crests corresponding to two periods of precipitation (4-10 July and 15-23 July) (24).

The nationwide toll for both the Oder and the Vistula floods of the summer of 1997 was an all-time high as far as economic losses are concerned. There is no official figure for material losses and the estimates range from 2 to 4 billion US$, indicating that the costs were of much significance to the national economy. The number of fatalities reached 54. The number of flooded towns and villages was 2592 (1362 totally and 1230 partially inundated). The flood caused damage to 46,000 houses and apartments. The number of evacuees was 162,000. Around 665,000 ha of land were flooded, of which over 450,000 ha consisted of agricultural fields (24).

Some 480 bridges were destroyed and 245 damaged. The flood resulted in serious damage to roads and railways, of the order of 3000 km and around 2000 km, respectively. Loss of 1900 cattle, 5900 pigs, 360 sheep and around 1 million poultry was recorded. Embankments were damaged or seriously weakened for a distance of about 1100 km. Due to destruction of 169 sewage treatment plants, it is estimated that, at the end of July, some 300,000 m3 of untreated sewage entered the river in one day (24).

Committees were unable to cope effectively with a gigantic flood, greatly exceeding their expectations and capabilities. The rescue operation during and after the flood was the biggest civil and military operation in Poland since the World War II. The flood relief programme has been labelled as the largest humanitarian action in the history of Poland (24).

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 (29).

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

IPCC conclusions

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 (29).

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 (25).

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 (26).

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 (26).

Adaptation strategies - Poland

Poland, caught by surprise in massive floods in 1997, resolved to face future weather extremes better prepared. A Flood Emergency Project, supported by the World Bank and the European Bank for Reconstruction and Development, included development of a monitoring, forecasting and warning system, flood prevention planning, and upgrading of flood prevention infrastructure. It also supported development of non‐structural measures to limit damage, including regulations for economic use of risky areas, flood impact minimization plans prepared by local communities and groups, warning systems, and flood insurance, among other measures (28).

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 (27).

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.

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Poland.

1. Hoyois and Guha-Sapir (2003), In: Anderson (ed.) (2007)
2. Anderson (ed.) (2007)
3. Mitchell (2003)
4. Barredo (2009)
5. Höppe and Pielke Jr. (2006); Schiermeier (2006), both in: Barredo (2009)
6. Höppe and Pielke Jr. (2006), in: Barredo (2009)
7. Becker and Grunewald (2003); Glaser and Stangl (2003); Mudelsee et al.(2003); Kundzewicz et al.(2005); Pinter et al.(2006); Hisdal et al.(2007); Macklin and Rumsby (2007), all in: EEA, JRC and WHO (2008)
8. EEA, JRC and WHO (2008)
9. Wang et al.(2005), in: EEA, JRC and WHO (2008)
10. Milly et al. (2005), in: EEA, JRC and WHO (2008)
11. Hisdal et al. (2007), in: EEA, JRC and WHO (2008)
12. Ramos and Reis (2002), in: EEA, JRC and WHO (2008)
13. Barnolas and Llasat (2007), in: EEA, JRC and WHO (2008)
14. Lehner et al.(2006); Dankers and Feyen (2008b), both in: EEA, JRC and WHO (2008)
15. Christensen and Christensen (2003); Kundzewicz et al.(2006), both in: EEA, JRC and WHO (2008)
16. Palmer and Räisänen (2002), in: EEA, JRC and WHO (2008)
17. Kay et al. (2006); Dankers and Feyen (2008), in: EEA, JRC and WHO (2008)
18. Andréasson, et al. (2004); Jasper et al.(2004); Barnett et al.(2005), all in: EEA (2009)
19. Arnell (2004); Milly et al. (2005); Alcamo et al. (2007); Environment Agency (2008a), all in: EEA (2009)
20. Dankers and Feyen (2008), in: EEA (2009)
21. Mudelsee et al. (2004)
22. Bronstert et al.(2000), in: Mudelsee et al. (2004)
23. Mudelsee et al. (2003)
24. Kundzewicz et al. (1999)
25. Ciscar et al. (2009), in: Behrens et al. (2010)
26. Kundzewicz (2006)
27. Kundzewicz (2002)
28. World Bank Group (2009)
29. IPCC (2012)