The aim of this study is to clarify seasonal effects of precipitation and temperature on groundwater level changes in monitoring stations of the Latvia University of Agriculture - Mellupīte, Bērze and Auce. Groundwater regime and level fluctuations depend on climatic conditions such as precipitation intensity, evapotranspiration, surface runoff and drainage, as well as other hydrological factors. The relationship between precipitation, air temperature and groundwater level fluctuations could also lead and give different perspective of possible changes in groundwater quality. Using mathematical statistics and graphic-analytic methods it is concluded that autumn and winter precipitation has the dominant impact on groundwater level fluctuations, whereas spring and summer season fluctuations are more dependent on the air temperature.

The long-term annual regime of shallow groundwater levels is analysed in two different time periods according to the dominance of continental and oceanic air masses in Latvia. Observed and modelled long-term mean monthly groundwater levels for the reference period (1961-1990) and a future period (2070-2100) are transformed into relative values and the contours are derived for each month of the year. In both periods, the main difference between the mildly oceanic western coastal part of Latvia and the continental eastern part is the pattern of the winter regime which responds differently to snowmelt. In the coastal areas, where the degree of climatic continentality is low, groundwater levels during the winter are higher than those areas in the inland eastern part of the country. From May to September, there is only temporal difference between the groundwater levels in those two parts of Latvia. There are significant differences of relative groundwater levels between reference and future periods during the winter months.