Vízügyi Közlemények, 2000 (82. évfolyam)
2. füzet - Illés L.-Konecsny K.: Az erdő hidrológiai hatása az árvizek kialakulására a Felső-Tisza vízgyűjtőben
196 Illés L.—Konecsny К. feladatai. Ukrán-magyar erdészeti és vízügyi konferencia előadásai. 1999. június 08-09. Nyírerdő Rt. Nyíregyháza, 2000. Sztoyko S.: The causes of floods in the Ukrainian Carpathians and the system of ecological measures of their prevention. (A vízáradások okai az Ukrán Kárpátokban és ökológiai intézkedések rendszere, azok megakadályozására.). CERECO'97. The 2 n d International Conference on Carpathian Euroregion Ecology. Miskolc-Lillafüred, 1997. Velcea I.: Tara Oasului. Studiu de Geografie fizica sí economica. (Avas-vidék. Természet- és gazdaságföldrajzi tanulmány). Edit. Academiei. RPR. Bucuresti , 1964. Zólyomi В.: Magyarország természetes növénytakarója. Kartográfiai V. Budapest, 1981. * * * The effect of forests oil the generation of floods of the Upper Tisza river basin by Lajos ILLÉS С. E. and Dr. Károly KONECSNY geographer The drainage basin of the Upper Tisza River (upstream of Tivadar) falls into the territory of three countries: 61.7% (7740 sqkm) into Ukraine, 36.2% (4540 sqkm) into Rumania and only 2.1% (260 sqkm) into Hungary. The effect of forests on the water budget needs to be analysed mainly from the point of view of runoff generation, although their role is not unambiguously interpreted. The canopy, the undergrowth and the roots retain considerable water volume, increasing also the quantity of infiltration water. The forest also significantly defines the accumulation of snow. The hydrological role of the forests of the Carpath Mountains (Figures 2. and 3.) has been studied by Ukrainian researchers since 1959, in the experimental catchments of Szolyova and Hripeliv. They found that although forests affect the ecohydrological character of the basin considerably, they cannot alone prevent the hazards of the generation of catastrophic floods (Tables I—III). Rumanian researchers arrived to similar conclusions (Tables IV-VII). Figure 4. shows the variation of Hungarian forests during 1,100 years, while their distribution in 1890 is illustrated in Figure 5. Figure 6 illustrates the relationship between inundated areas and forest areas. The forests of the plains of Szatmár-Bereg, belonging to the Upper Tisza catchment, are shown in Figure 7 and 8. Figure 9 shows the variation of forested areas and water surface areas of Szabolcs-Szatmár-Bereg County in the period 1850-1987. In order to protect the natural values of the Hungarian part of the Upper Tisza catchment, the area has been declared a landscape-preserve ( Table VIII.). The state of these forests in 1896 is shown in Table IX. A comparison of the conditions of the forests ín 1998 and in 1896 is summarised in Table X. Although these changes are not substantial they affect the passing of flood waves considerable. The effect of forests on the water regime and water budget was analysed in terms of water level and discharge time series. The following conclusions were arrived at: - The 146 year time series of annual precipitation of Nyíregyháza station shows a 0.4 mm/year decreasing trends (Figure 12). - The annual precipitation has been increasing during the past 50 years in the northern part of the Hungarian Plains Alföld (Figure 13), while the flows of the Tivadar station of the River Tisza also increased (Figure 14). - No relationship between the decrease of forested areas and the increase of river flows could be identified, since the significant decrease lasted only until the mid 1950-ies and was even reversed at certain locations. * * *
