CHANGES OF DRAINAGE RUN-OFF HYDROLOGICAL REGIME IN GLACIAL LACUSTRINE CLAYS OF THE KARST ZONE

Long-term data (1976 to 1999 and 2009) on the hydrological regime change of the drainage situated in glacial lacustrine clay loam on clay in the North Lithuanian karst zone are presented in the article. Study data shows that the drainage run-off changed since 1988. Before 1988 the average drainage run-off was by 19 mm higher than 1988, the insignificant difference (Stjudent's test t(act)=0.58<t(0.05)=1.72). However, seasonal distribution of drainage run-off changed significantly in the latter period. Due to changing climatic conditions the drainage run-off increased in winter (January-February), decreased in spring (March-May) and autumn (September-November). In the period of 1988-1999 the average air temperature and precipitation exceeded the corresponding data of 1976-1987 by 1.3 degrees C and 34 mm, respectively. Significant increase of the average air temperature (4.8 degrees C) was observed in January and February, that of precipitation - in February (16 mm). The influence of air temperature fluctuations on the drainage run-off was significant in January and February, that of precipitation in March, September and October. According to Mann-Kendall test (MK), the drainage run-off significantly increased in January (MK=2.28, significance level alpha = 0.05) and in February (MK = 2.04, alpha = 0.05), and insignificantly decreased in March, April, September, October and November.