Extended Abstract (432K)P3.1
Analysing decadal land-cover change as a possible flood-inducing effect in the upper Tisza river basin in Eastern Europe
Rita Pongrácz, Eötvös Loránd University, Budapest, Hungary; and J. Bartholy, Z. Dezsô, Z. Barcza, and I. Bogardi
After a 20-30-year-long dry period in the last few years several serious flood events (Autumn, 1998; Spring, 1999, 2000, and 2001) occurred at the watershed of the Ukrainian and Hungarian parts of the river Tisza. The water level at many stations exceeded the previous historical record values during these recent floods. Because of severe social, economical consequences of recent floods, enhanced public interest appeared to analyse and clarify the complex relationships between flood events and their possible reasons. In order to fulfil this demand several aspects of recently increased flood frequency and intensity must be scientifically investigated. They include recent very intense clear cutting of forest at headwaters (on steep slopes of the Eastern Carpathian Mountains), increased frequency of storms with intense precipitation, change in annual precipitation distribution over subcatchments, longer and colder winter with considerable snow accumulation, regional effect of global warming, etc. In this paper one of the potential effects is analysed, namely, the land-cover change of the upper part of the Tisza river basin. This area is shared by four countries (i.e., Romania, Ukraine, Slovakia, Hungary), the analysis presented here is accomplished on a subcatchment basis. For the separation of the watershed areas of tributary streams of the river Tisza the HYDRO1k Elevation Derivative Database has been used. In case of a 28,000 km2 large area it is obviously impossible to rely solely on ground-based measurements to estimate land-cover change. Therefore, remotely sensed satellite information must be considered, which guarantee appropriate spatial coverage for the seven selected subcatchments. In order to compare land-cover features between 1992-93 and 2000-01 the NOAA Global Land Cover Characteristics Data Base and the MODIS Land Cover Product have been applied. The aim of the analysis presented here is to answer whether or not the forest area at the headwaters of the river Tisza noticeably decreased during the last decade. Based on the results the following conclusions can be drawn. (1) Forest area decreased by 3-4% on average in the watershed of the Upper-Tisza river outside of Hungary, which means 1,200 km2 area out of the entire 28,000 km2 large area. (2) In the eastern/southeastern subcatchments forest area decreased during the last decade by about 10% of the total area, specifically, by 18% (900 km2), 5% (340 km2), and 12% (225 km2) at the Upper-Tisza in Romania, at the Upper-Tisza in Ukraine, and at the Borsova subcatchment in Ukraine, respectively. (3) Slight increase of forest area is detected in the western/northwestern subcatchments resulting in about 300 km2 larger forests. (4) Besides forest area other land-cover classes changed as well. Specifically, spatial extension of croplands decreased considerably (by 3,800 km2), while area of non-forest natural vegetation and cropland/natural vegetation mosaic increased by 1,700 km2 and 3,300 km2, respectively. Built-up area and water/snow/ice surfaces did not change significantly during the last decade.
Poster Session 3, Hydrometeorology Posters (Including Orographic and Scale Issues) (Hall 4AB)
Thursday, 15 January 2004, 9:45 AM-11:00 AM, Hall 4AB
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