Vízügyi Közlemények, 2000 (82. évfolyam)

3-4. szám - Nováky Béla: Az éghajlatváltozás vízgazdálkodási hatásai

Az éghajlatváltozás vízgazdálkodási hatásai 445 Impacts of climate changes on water management by Prof. Dr. Béla NOVÁKY hydrologist Having stepped into the third millennium one of the major challenges of water management is the facing of climate changes. Climate changes are caused by the pollution of the atmosphere by various human activities. The pollutants emitted increase the green

:house effects, the planetary albedo, thus increasing the global temperature. According to the annual report of the IPCC of 1995 the rate of probable average global temperature increase will be 0.1-0.35 °C/decade. The consequences of global climate change in Hungary were analysed and forecasted using various methods: trend analysis; regression analysis between the climate elements of the hemisphere and that of Hungary; analysis of paleoclimatic data; use of regional energy and water budget models; interpolating between the results of general atmospheric circulation models. Climate change scenarios of Hungary forecast a warmer climate, with more precipitation in the winter and a drier summer. The aridity of the region is likely to increase and the tendency of drought will be strengthened ( Table /.). Climate changes of the catchment of our large rivers, falling outside the country, are estimated with high uncertainty only. Table II. summarises the past changes of land uses, having an impact on the hydrological conditions. After joining the European Union further changes in the land uses will be expected. The details of these changes are not yet known. Impacts of climate changes on the hydrological conditions were analyses by several methods: (1) by the conceptual model HOLV-TAPI of daily time step, used for operative prediction in the Hungarian practice, for estimating the impact of climate change on the seasonal variation of runoff. (2) By regression models for estimating the impact of precipitation changes on the low-flow conditions of the end-of-the-summer, early fall. (3) By existing areal relationships for estimating the impacts on annual average runoff and on the excess inland waters of the end-of-the-winter-early-spring period. Partial verification of the models was made by comparing the results made by the independent use of various models (Table III.) and on the basis of analogies of periods selected from past records. The stability of the model was assumed for all models. The analysis of the impacts of climate changes resulted in the following conclusions: ( 1 ) Annual runoff might decrease at a rate exceeding the rate of precipitation decrease (Table IV.). (2) Seasonal variations within the annual runoff are expectable: summertime runoff will decrease at a rate larger than that of the annual runoff. (3) The peak flow and total volume of the first snow-melt flood is likely to increase, due to earlier snow-melt. (4) No substantial changes in the end-of-winter-early-spring time excess waters are expectable; - smaller decrease is expectable in the first part of the period investigated, followed by smaller increase in the second part, in the north-western part of the country (Table V). (5) The surface area of several small lakes will be likely to decrease, due to increasing evaporation. A number of the low-land lakes of the plains Alföld might run dry, while the water exchange rates of the large lakes (Balaton, Velence and Fertő) will be slowing down. (6) Results of the MINEQL model indicate that the increasing carbon-dioxide concentration might result in the increase of the salt content and hardness of the lakes. The warming up of climate might have a considerable impact on water users (on the specific consumer rates). Especially the increasing demand for irrigation water might be expected upon the changes of the climate (Table VI.). The expectable impact was assessed with the help of the Climate-impact function of the so called "water supply factor", which is a ratio