The present climate

Bulgaria includes 31% lowlands (0–200 m), 41% hills (200–600 m), 25% highlands (600–1,600 m), and 3% mountains (>1,600 m) (2).

The country is split into northern and southern Bulgaria by the Balkan Mountains. The climate is continental in the north and close to Mediterranean in the South. The annual amount of precipitation is between 500 and 650 mm, with precipitation ranging from 440 to 1020 mm. The highest monthly values are measured in June (at some places in May), with mean totals between 55 and 85 mm. February (or March) is the driest month, with mean totals between 30 and 45 mm (1).

The continental influence, stronger during the winter, produces abundant snowfall; the Mediterranean influence increases during the summer and produces hot, dry weather. The barrier effect of the Balkan Mountains is felt throughout the country: on the average, northern Bulgaria is about one degree cooler and receives about 192 more millimetres of rain than southern Bulgaria (2).

Bulgaria has five climatic zones - Moderate Continental, Intermediate, Continental-Mediterranean, Maritime and Mountainous. The main factor distinguishing the first three zones is the latitude, the terrain for the mountainous and the Black Sea for the maritime. The coastal climate is moderated by the Black Sea, but strong winds and violent local storms are frequent during the winter. Winters along the Danube River are bitterly cold, while sheltered valleys opening to the south along the Greek and Turkish borders may be as mild as areas along the Mediterranean or Aegean coasts (2).

The monthly mean temperature varies from -10.9 to 3.2 C in January and from 5.0 to 25.0 C in July. The highest readings are usually taken in the towns of Rousse and Silistra, sometimes reaching above 35°C (2).

Air temperature changes until now

Generally, there is no significant overall trend of mean annual air temperature in Bulgaria for the 20th century (6). Warming is observed, however, from the middle of 1980s. In fact, since 1997 all annual temperature anomalies are positive. 2007 was the warmest year recorded during the period of measurements in Bulgaria: temperature was 1.6⁰C above the average over the period 1961-1990. The years 1994, 2000, 2002 and 2009 were among the warmest years on record in Bulgaria (2).

In the eastern Mediterranean, the intensity, length and number of heat waves have increased by a factor of six to eight since the 1960s (9).

Precipitation changes until now

Annual precipitation varied considerably from year to year in the 20th century (6). Climate in Bulgaria became drier at the end of the 20th century. During the last decade however, precipitation totals have increased. Heavy rains caused severe floods damaging various socioeconomic sectors (2).

An investigation of change in snow cover (maximum depth and snow cover duration) over the 1931–2000 period was carried out at sixteen climate stations located in mountainous areas of Bulgaria. The mountain climate has been characterized by widespread warming and decreased winter precipitation over this period. However, there was no evidence of similar large-scale reductions in snow depth or snow cover duration: some sites showed significant decreases in snow cover, some no change, while others showed significant increases. Further analysis is required to understand the reasons for the varied response of snow cover to a changing climate (3).

The mountain climate is characterized by warming in all regions with significant reductions in winter precipitation in many mountain areas (3). Statistically significant reductions in annual precipitation for several Bulgarian mountain stations were reported before (4). Similar findings have been reported from other regions of European. Decreasing trends in annual and seasonal precipitation have been observed in the central and southern areas of Italy, for instance, especially during the second half of the 20th century (5).

Air temperature changes in the 21st century

Significant summer warming is expected in the western Balkan countries. Climate change projections indicate that air temperatures in 2080 during this time of the year increase between 5 and 8°C with respect to 1961-1990 over most of the countries in the peninsula. The number of summer days is projected to increase up to 90 days in the period 2021-2050. The percentage of summer days is projected to rise from 18-20% nowadays to more than 40% in most flat locations in southern Bulgaria. Probably, the number of hot days will increase as well, up to 30 % till the end of the 21st century (2).

Projections of air temperatures at three mountain stations (from several regional climate models based on the SRES A1B scenario) for 2065–2094 show a rise of 2.8 to 3.2 °C compared to the period 2001–2011. This increase is mainly due to the summer months (13).

Winters will be milder in the next decades and the number of ice days will decrease (2).

Eastern Mediterranean and the Middle East (EMME)

For the Eastern Mediterranean and the Middle East an analysis was carried out of long-term meteorological datasets (period 1901-2006) along with regional climate model projections for the 21st century (SRES scenario A1B) (7). The results suggest a continual, gradual and relatively strong warming of the area of about 1-3°C in the near-future (2010–2039), to 3–5°C in the mid-century period (2040–2069) and 3.5–7°C by the end of the century (2070–2099). Daytime maximum temperatures appear to increase most rapidly in the northern part of the region, i.e. the Balkan Peninsula and Turkey. Maximum day time temperature increases more strongly than mean night time minimum temperature (11).

Extremely high summer temperatures are projected to become the norm by 2070–2099; the coolest summers at the end-of-century may be warmer than the hottest ones in the recent past. As an example, the hottest summer on record in Athens in 2007 would be among the 5% coolest ones by the end of the century (7,11). The relatively strong upward trend in the northern parts of the Eastern Mediterranean and the Middle East indicates a continuation of the increasing intensity and duration of heat waves observed in this region since 1960 (8). According to regional climate model results based on the IPCC SRES scenarios A1B, A2 and B2, the number of heat wave days, here defined as days with maximum temperatures exceeding the local 90th percentile of the reference period (1961–1990), typically increases by a factor of 4–10 by the middle and 7–15 by the end of the century, with the strongest increases in the Middle East (11).

Current and future daytime mean temperature trends in the Eastern Mediterranean and the Middle East typically vary from 0.28° to 0.46°C per decade. The largest increases appear in some continental locations such as Belgrade, Sofia, Ankara, Baghdad and Riyadh with trends in excess of 0.4°C/decade. The same analysis was performed for daytime maximum and night-time minimum temperature; for daytime maximum temperature the largest upward trends are calculated for Belgrade, Sofia, Tirana and Ankara with 0.48°, 0.46°, 0.45° and 0.44°C per decade, respectively. For night-time minimum temperature, large positive trends exceeding 0.40°C/decade are derived for Belgrade, Riyadh, Baghdad, Athens, Sofia and Ankara (7,11).

A1B scenario results suggest that by the end of the century, the frequency of very hot days (maximum day time temperature >35°C) may increase up to 1–2 weeks per year in mountainous parts of the northern EMME and by about a month in much of the rest of the region. The frequency of ‘‘tropical’’ nights (mean night time minimum temperature > 25°C) also increases strongly, by nearly a month per year in the Balkans and coastal areas, and more than two months in the Gulf region, exacerbating the daytime heat stress. By the end of the century in most cities, the coolest summers may be warmer than the hottest ones today (11).

Precipitation changes in the 21st century

Only precipitation in February and March as well as December is expected to increase during the 21st century (2). For three mountain stations, projections of annual precipitation amounts for 2065–2094 show a decrease of about 7 to 17 % compared to the period 2001–2011 (from several regional climate models based on the SRES A1B scenario) (13).

Eastern Mediterranean and the Middle East

From the analysis of long-term meteorological datasets (period 1901-2006) along with regional climate model projections for the 21st century (SRES scenario A1B) a decline of annual precipitation is projected of 5–25% in 2040–2069 and 5–30% in 2070–2099 relative to the reference period 1961–1990 (7). The decreases will be particularly large (>15%) in Cyprus, Greece, Israel, Jordan, Lebanon, the Palestine territories and Syria. As a result of precipitation decrease, and also due to population growth rates, the per capita available internal water resources may decline strongly, for example by 50% or more by mid-century in Cyprus (12).

In the Balkans, Turkey, Cyprus, Lebanon and Israel, the number of rainy days may decrease, e.g. by 5–15 days at mid-century and by 10–20 days per year at the end-of-century (7). This appears to be a continuation of a trend observed in Greece since about 1960 (9).

The intensity of precipitation (maximum amount of rain per day) is expected to decrease except over the northern Balkans and the Caucasus (7).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Bulgaria.

1. Alexandrov (1999)
2. Ministry of Environment and Water (2010)
3. Petkova (2004)
4. Koleva and Iotova (1992), in:Petkova (2004)
5. Brunetti et al. (2000), in:Petkova (2004)
6. Alexandrov and Genev (2003)
7. Lelieveld et al. (2012)
8. Kuglitsch et al. (2010), in: Lelieveld et al. (2012)
9. Nastos and Zerefos 2009, in: Lelieveld et al. (2012)
10. Kuglitsch et al. (2010), in: Coumou and Rahmstorf (2012)
11. Lelieveld et al. (2013)
12. Chenoweth et al. (2011), in: Lelieveld et al. (2013)
13. Nojarov (2015)