About the Climate
Bulgaria has quite specific geographic situation, being in the easternmost part of Europe, rather close to the Asian continent and near the subtropical Mediterranean region. It gives grounds for rapid change of the climate from north to south. In climatic aspect the major part of the country belongs to the European moderate-continental zone. The southernmost and southeastern regions are under strong influence of the Mediterranean continental-subtropical zone.
Bulgarian river watersheds belong to three major basins: the Danube river basin (most of the rivers in North Bulgaria); the Black Sea basin (most of the rivers in East Bulgaria); Aegean Sea basin (most of the rivers in Central and South-West Bulgaria). The position of those three basins is shown by different color tones on the figure below. The precipitation is annually distributed, the high and low flow periods are quite well outlined, mostly because of the evaporation conditions.
Generally the high flow of the rivers under the Mediterranean influence is in December–January. These are the southernmost parts of the Aegean Sea basin. The low flow period of those rivers is quite dry because of the corresponding distribution of the rainfall and better evaporation conditions.
The high flow period of the rivers under the Continental influence is at April–June. These are the rivers of the Danube river basin, in North Bulgaria. The low flow of those rivers is higher than that of the rivers in the South.
Significant influence on the annual distribution of discharges has the permanent snow cover, which is formed in high mountains during winter season. Snow pack accumulates winter precipitation thus transferring water from winter season to late spring and early autumn.
Some examples of the different types of averaged annual hydrographs are given below. The outlined types of the distributions described above or some mixture of them is to be seen on them.
The lowland areas are usually used for agriculture, while the mountain areas are covered by different types of forests. About 30 % of the Bulgarian territory is covered by well karstified carbonate rocks. Only in the karstic areas the rivers may dry up during hot season. Another important issue is related to artificial regulation of river flow. More than 60 % of the total run-off is subject of different types of seasonal and annual regulation by dams, derivation channels and other hydrotechnical structures.
The winter snowfalls are considerable in Bulgaria under the combined influence of a Mediterranean cyclone and anticyclone or ridge from the North. Combined with strong winds, the snowfalls often cause dangerous situations on the Northeast of the country and in the high mountains as well. Intensive snowmelt due to the combine influence of warming and rainfall sometimes causes disastrous floods at certain Bulgarian rivers. Hailstorms quite often create dangerous conditions and significant economic losses. According to the climatic conditions certain parts of the country might be classified as semi-arid. Nevertheless there are almost no rivers drying during hot season (except in the karst areas), the low flow discharges are usually 50 times smaller than those of the high flow. So, droughts are among the dangerous phenomena in Bulgaria. Mostly because of the anthropogenic factors, certain regions suffer of insufficient drinking water resources.
The Principal for all the issues related to water is the Ministry of Environment and Water. Water in Bulgaria is a state property and the same principle is the basis of the Water Law. So the Ministry is actually the owner of this national resource, it gives permits to the water users, it deals with the short and long term planning in the field and keeps the national balance of the resource. There are several organizations in the field ensuring the rolling mechanism of the water affairs, which are given in the principle scheme below.