Water balance of Slovenia 1971 – 2000

The water is becoming more and more valuable natural resource. The increasing water demand and climate changes are making water a precious and not always available valuable. The water balance is the most appropriate way to make a full overview of water cycle in Slovenia, to find general information about hydrological characteristics of drainage basins, precipitation, evaporation and runoff. The article presents the methodology and the results of the Water balance project of Slovenia. Slovenia has the geographical position at the juncture of 4 main European georegions: The Alps, the Panonian Basin, the Mediterranean and the Dinaric Mountains. This makes the territory very diverse also from a hydrological point of view. Our major watershed divides the precipitation runoff into two watershed areas – the Adriatic Sea and the Black Sea. Due to this watershed almost all the Slovenia's rivers have headwaters in our territory. Water balance is calculation of water inputs and outputs over the defined area. The basic elements of the water balance include all the inflows and outflows for a given basin and serve for the computation of the water regime of a catchment area. It is defined by the parameters precipitation (P), evaporation (E), discharge (Q) and the change of the water reserves (dS). Main results of the water balance elements for the 1971 – 2000 period for Slovenia are: Average annual precipitation in Slovenia is 1579 mm, average annual evapotranspiration is 717 mm and calculated runoff is 862 mm. Compared to water amounts in the World, where the average precipitation is 750 mm, evapotranspiration is 480 mm and runoff is 270 mm, Slovenia shows an abundance of water quantities. Also the runoff coefficient with 55 % is much higher as 36 % of the world. The major questions remain if we are capable to live with this water amounts within the limits of sustainable development and what will be the effects of climate change to water balance.