abstract: The study presents analysis of changes in ten-day, month and half-year sums of precipitation (P), potential evapotranspiration (PET) and climatic water balance (CWB) defined as a difference between P and PET. Calculations for all ten-day periods during the summer half-year (IV-IX) were based on the measurements from the Wrocław-Swojec Agro- and Hydrometeorology Observatory in the period 1965-2000. Sums of potential evapotranspiration were calculated according to the original version of Penman's equation. Mean and extreme values, as well as standard deviation, were analysed in all periods under consideration. Linear trend equations were determined. They point at increasing tendency in potential evapotranspiration sums and decreasing tendency in precipitation sums during the analysed 36-year period. The biggest changes in time were observed in the case of climatic water balance, then in precipitation. The smallest change was seen in the case of potential evapotranspiration.