Cent. Eur. J. Geosci. • 2(4) • 2010 • 537-547 DOI: 10.2478/v10085-010-0029-0

Central European Journal of Geosciences

Flood hazard in Hungary: a re-assessment

Research Article

Dénes Lóczy∗

Department of Environmental Geography and Landscape Conservation, Institute of Environmental Sciences, University of Pécs, H-7624 Pécs, Ifjúság útja 6

Received 24 June 2010; accepted 21 September 2010

Abstract: Some decades ago the concept of flood hazard in the Carpathian Basin was interpreted solely as riverine flood hazard, mostly restricted to the Tisza and Danube Rivers, and was closely associated with the impacts of river flow regulation in the second half of the 19th century. Recent assessments, however, allow us to outline a more diverse picture. Climate change is predicted to bring about both an increase in the frequency of droughts and excessive rainfall events, resulting in irregulaties in the water regimes of rivers in Hungary. Excess water hazard from raised groundwater levels is found to affect much larger areas than previously thought. Recent strongly localized cloudbursts, point to the increasing significance of flash floods.Riverine flooding and excess water hazard are more common in lowlands, whereas flash flood hazards are primarily, but not exclusively, affect the mountainous and hilly regions of the country. This paper intends to assess the relative importance of the three types of inundation hazard analyzed and to illustrate their overall spatial occurrences by microregions on a map series. Keywords: water management • riverine floods • flash floods • excess water • Hungary © Versita Warsaw

1. Introduction affecting Central Europe [5]. The trends in the distribu- tion of precipitation (lower amounts of summer rainfall and at the same time, increasing intensity of rainfall events) and the resulting rises in water stages (Table 1) call for Time and time again repeated inundations (like the events a re-assessment of flood hazard in Hungary. It has been in the late spring of 2010) remind the public of the fact observed in several countries in Europe (for instance, in that the main environmental hazard in Hungary is flood- the United Kingdom [6]) that in addition to major riverine ing. Traditionally, flood hazard is conceived as more or inundations and design floods, the relative significance of less regular inundations along the major rivers. Extensive other types of inundation (by excess water and due to areas along both the Danube and its largest left-bank trib- flash floods) is growing. There is accumulating evidence utary, the Tisza, are highly exposed to riverine floods [1, 2] pointing to the significance of inundations of non-riverine and, consequently, flood control has always been a central origin. task of Hungarian water management policy [3, 4]. There are serious indications of climate change singnificantly

∗E-mail: [email protected]

537 Flood hazard in Hungary: a re-assessment

2. Objectives raphy of Hungary. Floods along the major rivers of the Carpathian Basin, the Danube, the Tisza and the Drava This paper is meant to explain the origin of the three types (generated by runoff from the mountain ranges encircling of flood hazard and to assess their relative significance the steadily subsiding Hungarian plains), continue to be over the territory of Hungary in the light of human inter- the most severe natural hazard threatening to inflict se- vention and predicted climate change. In order to outline rious damage to property. Temporal and spatial features the approximate geographic distribution of flood hazard, combine to produce a large-scale flood hazard. each type is represented at the level of microregions on a In the most comprehensive and often cited text on the map series. physical geography of Hungary [14] the origins of floods on the Danube are the following:

• the so-called ”green floods” in March and April 3. Methods (carrying floating leaved twigs) are controlled by snowmelt on the Alpine catchment; This paper combines two approaches: firstly it relies on the interpretation of general statements and research find- • the floods of May and June are due to prolonged ings on flood hazard (in publications mostly only available convective rainfalls; in Hungarian) and secondly it attempts to assess and map • ice-jam floods were theoretically possible in every the extent of the various types of flood hazard using dif- second or third year, when contiguous floating ice ferent methodologies, following recently formulated guide- covered the river (nowadays, however, ice cover is lines [7]: becoming less and less reliable on the Danube [15]); • The spatial extent of inundation hazard along rivers is estimated from inundation models based on flood • annual monthly water discharge shows a declin- frequency and its temporal trend [8, 9] for the last ing trend over the summer and reaches its minimum two decades. Floods on trunk rivers often result in October, then after a moderate rise in autumn in far-reaching effects (e.g. the backdamming of another minimum follows in December, when the smaller tributaries). Consequently, their impacts ground is frozen in the mountainous parts of the are not shown as a line or a band on the map but catchment. (The popular observation that most of instead the degree of hazard is projected as the the floods occur in the summer half-year is reflected total area of the microregion affected (even if only in the Hungarian name of localizations: ”summer partially). dykes”.)

• Excess water hazard estimation by microregions is More recently floods from snowmelt are particularly en- based on the maps of Imre Pálfai [10, 11], which hanced by the rain-on-snow phenomena (increasingly fre- used inundation frequency information for the peri- quent in the Alps as a consequence of more extreme win- ods of 1961 and 1980. Recent inundation history is ter weather oscillations) [15, 16]. Further recent assess- reconstructed from the GIS interpretation of remote ments [17–19] explain the increased hazard by the be- sensing sources (see e.g. [12]). lated snowmelt in the Eastern Alps overlapping with early summer flood waves, which are increasingly prolonged • Research on the conditions of flash floods has re- and thus, present considerable pressure on flood-control cently started. The methodology for survey and dykes. warning is now being elaborated [13]. In addition Flood hazard along a major tributary, the Drava River [20, to the interpretation of meteorological time series 21] is aggravated by and information from news sources, the survey of topographic and soil physical factors may be of rel- • snowmelt in the hilly Alpine foreland, evance for the preliminary delineation of the areas • followed by snowmelt in higher regions of potentially affected. the mountains (conveyed through the tributary Mura/Mur River), 4. Riverine flood hazard: spatial • Mediterranean cyclones causing a secondary peak and temporal aspects in October or November. Generally, a more serious flood hazard is recorded in the The changing interpetations of overall flood hazard are catchment of the Tisza, a typical channelized river [22– clearly detectable in the various text-books on the geog- 24]. In contrast with the Danube, which has no significant

538 Dénes Lóczy

Figure 1. Assessment of riverine flood hazard by the microregions of Hungary identified by Marosi S. and Somogyi S. [35] (by Lóczy, D. from data from Hydrography Yearbooks for 1987-2003, published by VITUKI between 1990-2006). Continuous lines indicate the borders of macroregions, dashed lines the borders of units lower in the hierarchy (meso- and microregions). 1 = lowland macroregions; 2 = hilly macroregions; 3 = mountainous macroregions; 4 = microregions with extensive active floodplain sections (regularly inundated); 5 = microregions with floodplains affected by the locally defined design flood;6=otherpotentially affected microregions.

tributaries along its Hungarian section,the flood pattern has also been formulated in the Government Decree # of the Tisza River is fundamentally influenced by a range 2006/1973 [32]:that benchmark flood is an ice-free river of tributaries [25]. The peculiar features of floods along water level with a probability of occurrence characterized the Tisza are the following [25]: by a given return period [33]. The length of the return period is variable: • the passage rates of flood waves are highly variable on tributaries with different channel slopes and are • along main flood control dykes: 100 years; more often superimposed on flood waves of the trunk river; • in urban and industrial areas: 120-150 years;

• consequently, prolonged flood waves increase dyke • in priority areas (e.g. near the capital city): 1000 breach hazard; years and

• the Tisza impounds the flow of tributaries along • for less valuable protected areas: 60-80 years. dozens of kilometres and causes inundations along their lowermost sections; For instance, the level of the destructive 1954 ice-jam flood is regarded as the 100-year design flood for the Danube • changes in the type and pattern of precipitation section between Esztergom and the southern border of may result in floods even in winter time. Hungary [34]. Riverine floods are usually conceived as flood waves pass- Within the territory of Hungary (93 030 km2), 21 248 km2 ing along the whole lengths of major rivers. However, the (22.8 per cent) are endangered by the 100-year return extent of local inundation hazard varies with the geomor- period flood of major rivers, primarily the Tisza and the phology of individual floodplain segments [26, 27]. River Danube [17], while 23 per cent of this area is largely pro- channel instability arises from excessive meandering and tected from inundation by the design flood. Another esti- channelization between too closely spaced dykes, hinder- mated 10 000 km2 of floodplain lies along smaller water- ing adjustment [28–31]. courses (10 per cent) and their extension has not yet been For the estimation of flood-prone area as well as for properly surveyed. Since drainage density is a character- planning flood-control measures, it is essential to de- istic property of physical geographical units, flood hazard fine the level of design flood. As this is also a politi- is presented in this paper for the microregions of Hungary cal issue, in addition to water management authorities it (Figure 1).

539 Flood hazard in Hungary: a re-assessment

Since the 1990s the floods (Table 1) followed one another damage in agriculture. Today excess water (also called within ”abnormally” short intervals, practically one ma- sheet flooding) is rather widely interpreted in Hungarian jor flood every year. This is an indication that riverine water management. In addition to raised groundwater lev- floods are still part of the natural hydrological system of els on the floodplains of major rivers during flood stages, the Carpathian Basin, motivated by several factors, both any other inundation in lowland areas is included [41]. natural and anthropogenic (36): The commonly used definition of excess water originates from rainfall or snowmelt which covers any extensive but • increasing flood discharges due to land use and temporary inundation of lowland areas and fully saturates climate changes in the upper catchments of major the soil. Whether soil saturation necessarily means sur- rivers; face inundation, remains an open question [42]. In recent decades, excess water hazard has been observed • reduced capacity of floodways as a consequence to increase dramatically [43] (Figure 2). The construc- of floodplain sedimentation and enhanced surface tion of artificial structures in the landscape [44] and the roughness [30, 34, 36–38]; neglected conditions of land drainage systems [45] all con- • the impact of drought years in the 1990s and 2000s tribute to the higher frequency of inundation in particu- on the (sometimes rather neglected) conditions of lar areas of the Great Plain. Excess water generation is flood-control-dykes. only partially related to high water stages along major rivers. In some cases it is the flood-control dykes them- Recent events prove that floods are not necessarily gen- selves which hinder the flow of excess water back to the erated by runoff in the mountain phase of the Carpathian river channel [46]. Basin. In May 2010 prolonged excessive rainfalls (amounts locally exceeding 300 mm per month, i.e. three- or four-fold the monthly average amount), which affected most of the Carpathian Basin at the same time, led to crit- ical situations along some medium-size and minor rivers (like the Kapos and tributaries in Southwest-Hungary and the Sajó, Zagyva and small streams in Northeast- Hungary with sources within Hungary). Property damage was caused by extensive housing and commercial devel- opments on the 100-year floodplain, which were granted permission from environmental authorities during drier pe- riods. In 2006 the Hungarian government passed legisla- tion preventing housing, industrial and commercial devel- opment in so-called ”high-water channel” areas (i.e. the channel which belongs to the design flood level or to the highest water level recorded to date [39]), as well as re- stricting insurance and the state flood-control pledge for property in flood-prone areas. The new decree ensures the priority of flood control considerations in land use op- tions. Figure 2. Map of excess water hazard for the Great Hungarian Plain (generalized after [10]). 1 = no excess water hazard; 2 = moderate hazard; 3 = medium hazard; 4 = severe hazard; 5. Excess water hazard 5 = active floodplain.

Excess water had been traditionally associated with river Inundation hazard from excess water is more difficult to flooding and perceived as the inundation remaining after delimit both temporally and spatially than riverine flood flood waves on rivers passed. Recently, the definition of hazard. Rapid snowmelt in spring and early summer and excess water [40] has been extended to include upburst- cyclonal rains are responsible for it. Although the aver- ing groundwater in the absence of a water-course. In a age depth and duration of snow cover is on the decline, more practical approach, the main criterion of excess wa- extreme values of such parameters often occur. The Na- ter inundation is that through surplus water inhibiting crop tional Water Management Framework Plan [45] includes root growth on agricultural land and creating prolonged a map of areas threatened by excess water inundation. reductive conditions in the root zone, it causes economic This map was later revised using topographic, geologi-

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Table 1. Peak water stages (cm above lowest ever mark) on major gauges of the Hungarian Tisza section in flood years and their rise (cm) between 1876-2009 (source: [18] and Research Institute for Environmental Protection and Water Management). Highest ever water stages are marked bold.

Gauge 1876 79 81 88 95 1919 32 33 47/8 70 79 98 99 2000 01 06 Rise (1876-2006) Tiszabecs 535 (650) 680 521 708 260 456 716 414 +181 Tivadar 704 684 684 744 714 690 752 707 848 865 805 958 772 783 1014 +310 Vásárosnamény 817 785 869 900 840 850 848 758 887 912 870 923 836 882 943 834 +126 Záhony 751 686 728 726 598 618 728 674 737 657 711 752 662 +1 Tokaj 784 755 780 872 815 854 856 695 781 858 880 872 894 928 847 893 +144 Tiszafüred 686 634 622 742 733 765 750 626 684 773 788 767 835 881 717 835 +195 Szolnok 753 763 764 818 827 882 894 662 784 909 904 897 974 1041 836 1013 +288 Csongrád 757 805 820 834 867 929 924 593 742 935 876 780 891 994 721 1033 +440 Szeged 786 806 845 847 884 916 923 660 714 960 842 705 817 929 660 1009 +349 cal, pedological, groundwater depth and land use data, as well as relying on the map of drainage ditch networks [47]. (Based on the remote sensing interpretation of recent in- undations, further revision is under way.) A simplified version of the excess water hazard map of Hungary (pro- cessed for Figure 2) identifies four categories:

• serious hazard, where inundations regularly recur in wet years;

• medium hazard, where one-time flood- ways,backswamps and swamps enclosed between alluvial fans are exposed to rising groundwater;

• moderate hazard, where natural levees in flood- Figure 3. Assessment of excess water hazard by microregions (by plains and lower sections of alluvial fans are oc- Lóczy, D. after [10]). For 1 to 3 see Figure 1. 4 = mi- cassionally affected; croregions with medium and locally serious hazard; 5 = predominantly medium hazard; 6 = predominantly mod- erate hazard locally with medium hazard. • no hazard areas, where permeable surface deposits (sands) prevent enduring inundation.

The first three categories make up more than 2 million 7 June, 2010, extensive damage was caused not only hectares in Hungary, i.e. one-third of the agricultural to agriculture but also to transport (railway embank- area. In some regions the built-up areas of settlements ments) and tourism (partly because of the proliferation are also affected [48]. When evaluating excess water haz- of mosquitoes). Public attention to excess water hazard ard individually for each of the microregions of Hungary, has increased and this may lead to more resources being an overview hazard map can be drawn (Figure 3). Natu- concentrated on the development of a warning and infor- rally, few microregions are threatened by excess water in mation system [49]. their entirety but the map indicates microregions where significant portions are affected. Excess water hazard even became a topic at the 2009 Eu- 6. Flash flood hazard ropean Parliament elections in Hungary. Some politicians called for the recognition of the damage caused by excess In a similar way, relatively recent events (highly restricted water by insurance companies in the same way as damage in area but causing disastrous floods in various parts of from riverine floods is treated. The May 2010 rainfalls also Hungary in the 1990s and 2000s – Figure 4, Table 2) have caused excess water inundations over 167 000 hectares given impetus to flash flood research [13, 49]. The aim area (Ministry of Environmental Protection and Water of investigations is to parametrize a model (Flash Flood Management information, http://www.kvvm.hu) and by Inundation Prediction Model, FLIP) which is capable of

541 Flood hazard in Hungary: a re-assessment

Figure 4. Percentage change in the number of days with extreme precipitation (20 mm d−1, RR20) in the Carpathian Basin for the period 1976-2001 compared to the period 1961-1990 at 95% confidence level (after [5]). For 1 to 3 see Figure 1. Percentage change per decade: a = -0.6– -0.3; b = -0.3–0; c = 0–0.3; d = 0.3–0.6; e = 0.6–0.9; f = 0.9–1.2; +25 = sites of extreme rainfall events as listed in Table 2.

Figure 5. Assessment of flash flood hazard (by Lóczy, D. after [49]). For 1 to 3 see Figure 1. 4 = high; 5 = medium;6=lowhazard.

rapid screening of the areal distribution of this hazard in occurrence of flash floods more probable than elsewhere. Hungary. The idea is that passive ground conditions (re- Although Table 2 lists several major cloudbursts for the lief, soil permeability, catchment geomorphology [50]) are lowland areas of Hungary, runoff conditions only gener- equally important in the generation of flash floods as the ate flash floods in the hill and mountain regions. The active triggering factor (intense and prolonged rainfall). reliability of the model depends on the resolution of in- In this approach it seems feasible to identify microregions put parameters, first of of which is the Digital Elevation where the interaction of environmental factors makes the Model.

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Table 2. Some major rainfall events in Hungary, 2005-2010 (by Lóczy D. from online news sources, monthly record precipitation from Hungarian Meteorological Service data).

Date Location (county) Topography Daily rainfall amount (mm) if >40 mm 12.10.2010 Kondoros (Békés) lowland 70 06.09.2010 Iklódbörd˝oce (Zala) hill 182 27.08.2010 Nyírlugos (Szabolcs-Szatmár-Bereg) lowland 107 01.07.2010 Balmazújváros (Hajdú-Bihar) lowland ca. 100 16.06.2010 Baja (Bács-Kiskun) lowland ca. 60 15-17.05.2010 Bakonyszucs˝ (Veszprém) mountain 240 in 3 days 12.04.2010 Várpalota (Veszprém) mountain 63 10.11.2009 Dunaföldvár (Tolna) lowland 77 12.10.2009 Mindszent (Csongrád) lowland 56 13.09.2009 Sajószentpéter (Borsod-Abaúj-Zemplén) hill 61 04.08.2009 Gacsály (Szabolcs-Szatmár-Bereg) lowland 89 15.07.2009 Kup (Veszprém) hill 74 11.06.2009 Taktaharkány (Borsod-Abaúj-Zemplén) hill 97 04.05.2009 Réde (Komárom-Esztergom) hill 63 08.08.2008 Kárász (Baranya) hill 68 23.07.2008 Bakonyszucs˝ (Veszprém) mountain 104 26.06.2008 Sopron (Gy˝or-Sopron) mountain 114 24.06.2009 Bozsok (Vas) hill 120 20.05.2008 Bátya (Bács-Kiskun) lowland 59 20.04.2008 Galgagyörk (Pest) hill 60 24.10.2008 Pocsaj (Hajdú-Bihar) lowland 55 18.09.2007 Murakeresztúr (Zala) hill 70 20.08.2007 Sárvár (Vas) hill >50 11.08.2007 Mez˝oberény (Békés) lowland 71 10.08.2007 Tengelic (Tolna) hill 94 04.06.2007 Baja (Bács-Kiskun) lowland 62 30.05.2007 Kisújszállás (Jász-Nagykun-Szolnok) lowland ca. 60 22.05.2007 Rád (Pest) hill 78 29.09.2006 Rábaúfalu (Gy˝or-Moson-Sopron) lowland 78 20.08.2006 Budapest mountain ca. 80 01.08.2006 Isaszeg (Pest) hill 93 29.06.2006 Vasvár (Vas) lowland 85 27.06.2006 Nógrádszakál (Nógrád) hill 107 22.06.2006 Budapest lowland 107 20.04.2006 Debrecen (Hajdú-Bihar) lowland 65 11.09.2005 Kecskemét (Bács-Kiskun) lowland 82 21-24.08.2005 Keszthely (Veszprém) mountain 132 in 3 days 04.08.2005 Mez˝ohék (Jász-Nagykun-Szolnok) lowland 164 11.07.2005 Máriabesny˝o (Pest) hill 154 09.05.2005 Bakonybél (Veszprém) mountain 63 04.05.2005 Mád (Borsod-Abaúj-Zemplén) mountain ca. 80 (30 in 15 minutes) 18.04.2005 Mátraszentlászló (Nógrád) mountain 111

543 Flood hazard in Hungary: a re-assessment

With accumulating evidence of climate change, flash floods • human activities on the catchment (deforesta- have been recognized recently as an increasing environ- tion, housing and infrastructure development, mental hazard in Hungary. In addition to being a highly narrowing-down floodplains); localized phenomena, their seasonal distribution is also • impacts of climate change (inclination to uneven. However, the summary map of this hazard indi- drought but growing intensity and unpre- cates that virtually all mountainous and hilly microregions dictability of rainfall). of Hungary are under threat (Figure 5), only runoff con- ditions cause some variation in the distribution of this Further research on the flood hazard impacts of var- hazard. The developers of the model are convinced that ious human activities and of climate change is re- with an increased set of parameters and a higher reso- quired. lution DEM, the prediction of flash flood events can be improved [13]. 2. When delimiting potentially inundated areas, in ad- dition to river floodplains, hill valleys with flash flood hazard and lowlands with excess water haz- 7. Flood control measures ard also need to be surveyed and monitored. 3. As in earlier historical ages, the adjustment of the Apart from raising dyke heights, the response to increased population to inundation is required. Although, riverine flood hazard, particularly on the Tisza River, is the maintenance of flood-control dyke systems and envisioned in several ways [19]: probably the establishment of emergency reservoirs • through amending water retention in the headwater can alleviate riverine flood hazard, it is practically areas (outside the borders of Hungary); impossible to avoid inundations from excess water or flash floods induced by local (convective or ad- • through enhancing the conveyance capacity of vective) cloudbursts, which may occur with an in- floodways; creased frequency in thefuture. Building and other land use regulations need to become stricter and • through river impoundment beyond dams; should be enforced without allowing for any excep- tion. • through constructing smaller emergency reservoirs (used as meadows or pastures in flood-free periods) along the trunk river and its major tributaries. Acknowledgements Emergency reservoirs represent a special category of con- finement. Confinement planning aims for the preven- The author is grateful for financial support from the Hun- tion, restriction or (at least) delaying of the inundation garian National Science Foundation (OTKA, grant num- of protected floodplain resulting from breaches of main ber: K 68903). The base map for the assessment maps defences [8]. Dynamic solutions for flood confinement are was digitized by Bettina Balassa and advice for draw- now being studied during the process of the supervision of ing the figures was provided by Ervin Pirkhoffer. Their plans [18, 51]. Along the Danube, the row of reservoirs of help is gratefully acknowledged. Funding received within the Austrian river section and the Cunovoˇ reservoir in Slo- the framework of the Baross Gábor Grant (# PTE_TM09; vakia are capable of reducing (but not eliminating) flood project leader: Szabolcs Czigány) is also appreciated. hazard in Hungary [2]. The legal opportunites to mitigate flood risk have already been mentioned. The prevention of damage from excess water inundation References and flash floods is a rather complicated issue. The de- velopment of monitoring and warning systems seems to [1] Lóczy D., Juhász Á., Hungary. In: Embleton C. be the way to follow if we want to avoid or prepare for Embleton-Hamann C. (Eds.), Geomorphological Haz- sudden disastrous events. ards of Europe. Elsevier Science Publishers, Amster- dam, 1997, 243-262 [2] Zsuffa I., Árvizek okozta kockázatok (Flood risks). 8. Conclusions Magyar Tudomány, 1999, 1, 29-36 (in Hungarian) [3] Kovács D. (ed.), Árvízvédelem, folyó-és tószabályozás, 1. Steadily rising flood levels along the major rivers víziutak Magyarországon (Flood control, regulation of are due to interacting reasons: rivers and lakes and waterways in Hungary). National

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