Bulgaria provides various habitats for amphibians. The country falls within six terrestrial ecoregions of the Palearctic realm: Balkan mixed forests, Rodope montane mixed forests, Euxine-Colchic deciduous forests, Aegean and Western Turkey sclerophyllous and mixed forests, East European forest steppe and Pontic-Caspian steppe. Bulgaria has varied topography. From north to south the main geomorphological regions are the Danubian Plain, the Balkan Mountains, the Sub-Balkan valleys, the Rila-Rhodope massif to the south-west, the Upper Thracian Plain and the Strandzha mountains to the south-east. The country has a dense network of rivers but with the notable exception of the Danube, they are mostly short and with low water flow. The average annual precipitation is 670 mm; the rainfall is lower in the lowlands and higher in the mountains. The driest region is Dobrudzha in the north-eastern part of the Danubian Plain (450 mm), while the highest rainfall has been measured in the upper valley of the river Ogosta in the western Balkan Mountains (2293 mm).