Drainage Runoff in Climate Change Context in Central Lithuania

Abstract

The size of drainage runoff depends on meteorological conditions of the year, the most important of which are the precipitation quantity and air temperature. However, the interdependence of precipitation quantity and drainage runoff is quite complex. Drainage systems are especially important in spring, during the snow melting period, because the excess of water is removed quickly from the arable layer of the ground, therefore, the conditions to start spring field works for about two weeks earlier are guaranteed. The article presents the influence of fluctuation of the main climatic factors over time on drainage runoff, the analysis of drainage runoff distribution in the course of a year in Central Lithuania. The seasonal differences of annual temperature amplitude and precipitation quantity decrease. It has a significant impact on the seasonal distribution of drainage runoff. The change of drainage runoff and its distribution over a year as well as the patterns of runoff have been analysed. The article analyses the nature of multi-year change of runoff during the last four decades – periodic fluctuations and change trends. The analysis of runoff observation data revealed that seasonality, typical for run-off change, remains, however, the drainage runoff during winter season has increased significantly over the past four decades. It was also influenced by growth of multi-year temperatures of all seasons, except autumn: the frozen soil is characterized by low water permeability, irrespective of its content. Water, present in thinner capillaries of clay and loam soil, freezes at lower temperature. An increased incidence of thaw of frozen ground demonstrates that water infiltration conditions of cold season must have changed