O slivu1

The Sava River Basin is a major catchment of the South Eastern Europe covering the total area of approximately 97,700 km2. It represents one of the most significant sub-basins of the Danube River Basin, with the share of 12 %. The basin area is shared among six countries: Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro and Albania. Except for Serbia and Albania, its watershed covers 45 to 70% of the national territory of the other four countries. Its water resources constitute nearly 80% of the total freshwater resources in those four countries.
Population of the five countries (Albania is not included since only negligible part of the basin area belongs to its territory) of the region is approximately 18 million, a half of which live in the Sava River Basin. In Slovenia 61% of the people live within the Sava River basin, in Croatia 50%, in Bosnia and Herzegovina 88%, in Serbia 26% and in Montenegro about 33%.

The Sava River basin is situated within a region characterized by the dominant moderate climate of the northern hemisphere, which is modified by the influence of relief. Thus, mountainous zonal climate characteristics are present especially in the eastern and southern part of the area. Cold and hot seasons are clearly defined. The winter can be severe with abundant snowfalls, while the summer is hot and long. Climate conditions within the basin can be classified into three general types:
- Alpine climate;
- Moderate continental climate;
- Moderate continental (mid-European) climate.

An alpine climate prevails in the upper Sava Basin in Slovenia. A moderate continental climate dominates in the right tributaries’ catchment areas within Croatia, Bosnia and Herzegovina and Montenegro, while a moderate continental (mid-European) climate primarily features in the left tributaries’ catchment areas that belong to the Pannonian Basin. Average annual air temperature for the whole Sava River Basin was estimated to be approx. 9.5°C. Mean monthly temperature in January falls to approx. -1.5°C, whilst in July it can reach almost 20°C. 

The precipitation amount and its annual distribution are fairly variable within the basin. The average annual rainfall over the Sava River Basin is estimated to be approximately 1,100 mm. The average evapo-transpiration for the whole catchment area is approx. 530 mm/year.
The landscape within the Sava River Basin is diverse. The general relief characteristics are illustrated below. Mountainous relief (the Alps and the Dinarides) dominates in the upper part of the basin, which belongs to Slovenia, and the southern part of the basin belonging to Montenegro and Northern Albania. The mountains of Montenegro include some of the roughest terrain in Europe. They average more than 2,000 meters in elevation and occasionally exceed a height of 2,500 meters (the peak of Bobotov Kuk in the Durmitor Mountains). The northern part of the Sava River Basin is situated in the Pannonia Plain, which is characterized by fertile agricultural land. The elevation of the Sava River Basin ranges between 71 m a.s.l. at the mouth of the Sava River in Belgrade (Serbia) and 2,864 m a.s.l. (Triglav, Julian Alps). The mean elevation of the basin is approximately 545 m a.s.l.
The Sava River is created from the Sava Dolinka and Sava Bohinjka.. From the confluence of these two rivers, near Radovljica in Slovenia, to the mouth the Sava River at Belgrade (Serbia) is 945 km long. In terms of length it is the third, in terms of basin area second, and in terms of flow the biggest Danube River's tributary. It flows from Slovenia to Croatia, then it forms the border between Croatia and Bosnia and Herzegovina, and to Serbia.
Common characteristic of almost of the right tributaries of the Sava River is their torrential behaviour, particularly in their upper sections, while left tributaries (except in Slovenia) drain mostly flat areas and low hills of the Pannonia Plain. The slopes and flow velocities of the left tributaries are smaller and the streams are meandering.
Spatial distribution of elements of hydrologic balance in the Sava River basin is heterogeneous. Long-term average annual precipitation ranges between 600 mm and 2,300 mm. The largest precipitations take place in far western sub-catchments (Sava Dolinka and Sava Bohinjka Rivers) and at upper parts of sub-catchments of the Kupa, Piva, Tara, Una, Vrbas, Drina and Lim Rivers. Areas with smallest precipitation are located in Slavonia, Srem, Semberija and the Kolubara River catchment. Spatial distribution of runoff largely follows pattern of spatial distribution of precipitation. It varies from 150 mm/year (under 5 l/s/km2) up to 1,200 mm/year (almost 40 l/s/km2). In general, the right tributaries of the Sava River are characterized by much higher water yield than the left tributaries (e.g. Una River 23 l/s/km2, Vrbas and Bosna Rivers 15 and 19 l/s/km2, Ukrina and Tinja Rivers, 12 l/s km2). The Drina River, as the largest tributary of the Sava River, due to high precipitation (long term annual average is over 2,000 mm) has a very high water yield: between 40 and 50 l/s/km2. The left tributaries (Krapina, Lonja and Orljava and Bosut Rivers) gets annually 700 – 1,000 mm of rain but relatively big evapotranspiration reduces unit-area runoff to just a few l/s/ km2, which at the hilly regions can rise to 12 l/s/km2. A long-term average unit-area-runoff for the complete catchment area of about 18 l/s/km2.
Average discharge of the Sava River at the confluence with the Danube River in Belgrade (Serbia) is about 1,700 m3/s.