Bulgarian Hydrology in a Few Words

In General

Bulgaria is situated in the South East Europe, in the central part of the Balkan Peninsula. The country has a long history since 681, when the first Bulgarian state was established by some mixture of Slavs residing on the Balkans and Bulgarians, coming somewhere from Asia. Later the state became a Christian Kingdom and suffered by Greek and Turkish invasion. After the Second World War it became a Socialist Republic and fall under the domination of the Soviet Union. The majority of population is Christian Orthodox while the biggest minority (about 10%) consists of Muslims. Since 1990 Bulgaria is a Parliamentary Republic, heaving a President with limited power. Now the country is facing severe economic shortages on its way to market economy. It has status of an Associated European Community member state and officially applied to join NATO.

About the Climate

Bulgaria has quite specific geographic situation, being in the Southeast outlying part of Europe, rather close to the Asian continent and the subtropical Mediterranean region. This 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 southmost and southeastern regions are under the strong influence of the Mediterranean continental-subtropical zone.

Hydrological Regime

The 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. Nevertheless the precipitation is relatively well 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 and January. Those are the South-most 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 and June. These are the rivers of the Danube river basin, at the Northern part of Bulgaria. The low flow of those rivers is higher than of those at the Southern part.

Significant influence on the annual distribution of the discharges cause the permanent snow cover which is formed in high mountains during the winter. The snow pack is accumulating the winter precipitation thus transfering water from the winter season to late Spring and early Autumn.

Some examples of the different types of averaged annual hydrographs are given below. There one can see more or less outlined the types of distribution described above, or some mixture of 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 a river may dry up during the hot spell. Another important issue is related to the artificial regulation of the river flow. More than 60 % of the total run-off is subject of different type of seasonal and annual regulation by dams, derivation channels and other hydro-technical structures.

Hazardous Phenomena

The winter snowfalls are considerable in Bulgaria under the combined influence of Mediterranean cyclone and anticyclone or ridge from north. Combined with strong winds, the snowfalls often cause dangerous situations in the Northeast part of the country as well as in the high mountains. Intensive snowmelt due to the combined 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 nearly there are no rivers drying during the hot spell (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.


State Principal

The state Principal for all the issues related to water is the Ministry of Environment and Water. Water in Bulgaria is state property and the same principle is the basis of the New Water Law, which was recently adopted by the Parliament. In this respect 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. More information on the National Institute of Meteorology & Hydrology is given in the Annex.


NIMH Organization Chart

Directory Board
Deputy Director
Deputy Director
Scientific Secretary Assistant Director

Meteorology Hydrology Weather forecasting Pollution SERVICES:
Maintenance; Publishing;
Construction; Library;
Services, telecommunication, etc.

Regional level
Branch Plovdiv Branch Varna Branch Pleven Branch Kiustendil
  • Synoptical - 40
  • ;
  • Climatic - 87;
  • Rainfall gauges - 289
  • ;
  • Agrometeorological - 25;
  • Hydrological - 209;
  • Hydrogeological - 106 springs; 335 wells.


NIMH Main Functions

The National Institute of Meteorology and Hydrology is the Bulgarian Hydrometeorological Service being part of the Bulgarian Academy of Sciences. The Institute has two main tasks. The first is to maintain operational meteorological and hydrological activities (monitoring, data processing, forecasting, telecommunication, etc.) to satisfy the needs of the country in such kind of information. The second task is to perform different investigations in meteorology, hydrology as well as environment related studies.

The new structure of the Institute, constituted a few years ago, ensures close interaction between the operational and the research staff. Almost all scientists are involved in the operational works which leads to a better quality of our products.

There are two levels of responsibility in the Institute: Headquarters situated in Sofia and four regional branches (Plovdiv, Varna, Pleven and Kjustendil) responsible for different country regions and more than 2000 different observing stations covering well the territory of those regions.

The Headqarters consist of several Research and Operational Departments (R&OD) and supporting branches. The R&OD play the main role in the development of the technology and methodology used in the operational activities of the Institute. They are divided in sections according to the specific tasks. Head of each R&OD is a senior researcher (usually with PhD or DSc degree)

Each one of the regional branches has the responsibility for about a quarter of the territory of the country. They consist of several sectors similar to the divisions in the headquarters. They deal mainly with operational activities. The branches are responsible for data collection from the stations, its primary quality check and transmission to the Central data processing unit. The regional branches also provide hydrometeorological services to the regional authorities and communities.

The basic observation networks, which are under operation, are as follows:

The Institute has a telecommunication center which functions as:

The RTC is one of the 15 regional centers of the GTS. It manages the exchange of meteorological and other types of data: hydrological, oceanographical, seismographic etc. Its main activity is to insure the information flow from countries of South West Europe and Greece, Cyprus, Romania, Turkey, Macedonia, ex Yugoslavia.

The main activities of the department of "METEOROLOGY" are devoted to the research of the atmosphere dynamics, the long range forecasting models, climatology, agrometeorology, meteorological and agrometeorological data banks, climate changes, data control and processing

The main activities of the department of "HYDROROLOGY" are devoted to the investigations of the water resources including surface and groundwaters, sediments, fluvial processes, hydrometry, hydrodynamics and hydrophysics of lakes and marine coastal waters, coastal circulation, etc. During the last several years studies were performed over the development of new methods for hydrological analyses and assessment of the hydrological aspects of the drought processes, flood frequency analysis, hydrological data processing, computerised data bank, hydrological forecasting, sediments and fluvial processes of the rivers in the Northern part of Bulgaria. The research staff is dealing also with the development of forecasting and warning systems mainly for high waters prediction, determination of general trends and forecasts for the ground waters, real time estimates of the country water balance parameters and preparation of the corresponding bulletins. Recently some studies were performed in the field of surface - groundwaters interaction and dissemination of chemical ingredients and pollutants, mainly in the Bulgarian cut of the Danube river basin. Recent years the research staff was engaged in several national and international projects sponsored by different national sources like: "The National Science Fund", Ministry of Environment, the former Water Council, The Government Commission for Civil Protection Against Accidents and Disasters as well as different international sources like the French and Spanish Governments, the British Council, the ECC "Copernicus", INCO and "PECO" programmes, WMO, UNESCO, EC PHARE and others. Operational duty of the staff is the supervising of the observation network in the field of hydrology.

In the department of "COMPOSITION OF THE ATMOSPHERE AND THE HYDROSPHERE (POLLUTION)" investigations are carried out over the chemical background of the atmosphere and the natural waters, small gas contents, dispersion of pollutants, modelling, ozone studies, chemistry and radio-nuclide content in precipitated waters.

The Weather FORECASTING DEPT. is responsible for the operational and research activities in the general weather forecasting, warnings for severe weather events as well as for implementation of some special forecasts type related to different fields of economy, road maintenance, marine forecasts, pollution dissemination including transboundary impact and so on. Both conventional and advance type of data (like satellite information) are used applying modern technology, numerical and statistical modelling, computerised visualisation and so on. More than the half of the staff is dealing with operational issue of the hydrometeorological short and medium range forecasts and relevant bulletins.

The NIMH represents Bulgaria in the World Meteorological Organization of UN. NIMH participates in several projects of WMO as: World Weather Watch; Global Telecommunication System; creation of National Meteorological Centers of Macedonia and Albania; forthcoming up-grading of the NMC of Moldova, Ukraine, Georgia and Armenia; regional projects for up-grading the observational network along the Black Sea coast and in the Mediterranean region - Med-Hycoas. NIMH participate in a number of other projects funded by national and international sources. Two WEB sites are under development: www.meteo.bg related to administrative and regime information and weather.meteo.bg related to operational data and forecasts.

Example of a WEB page of the site weather.meteo.bg