Basic data on the hydrology of Lakes Ohrid and Prespa

This paper deals with hydrological analyses of Lakes Ohrid and Prespa. The watersheds and the lakes themselves are shared by three countries: Albania, Greece and Macedonia. As a result of insufficient interstate scientific cooperation and inexistence of data exchange, the lakes and their watersheds are not fully investigated regarding hydrology and hydrogeology. This paper represents a first attempt at a complete hydrological analysis based on data from the Macedonian side. This is not considered to be a particular deficiency, because over 60% of the lakes' watersheds and the lakes themselves belong to Macedonia, where a great number of reliable and long-term data series of hydrometeorological observations exist. The Prespa lakes do not have surface outflow and are connected with Lake Ohrid by underground karst conduits. Because of this, from the hydrological point of view, the lakes and their watersheds cannot be analysed separately. The changes of the regime of the air temperature and the rainfall distribution have been investigated in this report. An increase of the maximum and decrease of the minimum annual air temperatures, as well as a decrease of annual precipitation sums has been determined. Also, a statistically significant descending trend of water level in both lakes has been confirmed, with a statement that the water level decrease in Lake Prespa is extremely alarming. From 1985 to 1995 the water level in Lake Prespa has dropped by more than 5 m. The main reasons for this cannot be identified easily because there are no data on water use quantities from all three countries. As the lakes represent unique natural, ecological and economical water resources in a region suffering water shortage, we plead for a strengthening of international support in activities on salvation of both lakes. A prerequisite for this is the water balance calculation and common cooperation in sustainable water resources management of the lakes. Copyright (c) 2006 John Wiley & Sons, Ltd.