The impact of climate variability and change on crop yield in Bulgaria
Introduction
During the recent decade, the issues of climate variability and climate change have been at the center of many scientific studies (Hulme et al., 1999). Global climate variability and change caused by natural processes as well as anthropogenetic factors, are major and important environmental issues that will affect the world at the beginning of the 21st century. The earth’s climate has exhibited marked ‘natural’ variations and changes, with time scales varying from many millions of years down to a few years. Over periods of 1 or 2 years, fluctuations in global surface temperatures of a few tenths of a degree have been recorded. Some of these are related to the El Niño-Southern Oscillation (ENSO) phenomenon; major volcanic eruptions have also had some impacts. The concentration of greenhouse gases in the atmosphere continues to increase. This is largely due to human activities, mostly fossil fuel use, land use change, and agriculture. In some regions, there is also an increase in the concentration of aerosols, which has an opposite effect on the radiative balances and tend to cool the atmosphere. About 64% of the warming effect due to greenhouse gas increase during the last 200 years, is caused by carbon dioxide. These changes in concentration of greenhouse gases and aerosols are projected to lead to regional and global changes in temperature, precipitation and other climate variables. This can ultimately result in global changes in soil moisture, an increase in global mean sea level, and prospects for more severe extreme high-temperature events, floods and droughts in many locations (Houghton et al., 1996).
Global climate change will affect all economic sectors to some degree, but the agricultural sector is perhaps the most sensitive and vulnerable. World agriculture, whether in developing or developed countries, remains very dependent on climate resources (Downing, 1996, Watson et al., 1996). The impact of climate variability on agricultural production is important at local, regional, national, as well as global scales (Kaufmann and Snell, 1997, Freckleton et al., 1999, Gadgil et al., 1999). Crop yields are affected by variations in climatic factors such as air temperature and precipitation, and the frequency and severity of extreme events like droughts, floods, hurricanes, windstorms, and hail.
Recent research has focused on assessments of the potential impacts of climate change on agriculture at different scales. For example, regional and global estimates of potential climate change on agricultural production were conducted by Harrison et al. (1995), Wolf and Van Diepen (1995), Easterling et al. (1996), Watson et al. (1996) and Adams et al. (1998). The effects of global climate change and possible adaptation measures have been described by Easterling (1996), Smith (1997), and Adams et al. (1999). Also several national assessments have been conducted by Rosenzweig et al. (1995), Peiris et al. (1996), Elmaayar et al. (1997), Davies et al. (1998), and Lal et al. (1999). Some of the climate change impact studies in eastern Europe were supported through the US Country Studies Program (Smith et al., 1996). Studies on the impact of expected changes in climate on agricultural production in Bulgaria have also been initiated by Alexandrov (1997).
The main goal of this project was to study climate variability during the 20th century and the impact on agriculture, and to determine the potential impact of climate change on agriculture in the 21st century in Bulgaria. Specific objectives included: to create new climate change scenarios for the 21st century in Bulgaria, to simulate the impact of climate variability and change for the major crops, including maize and winter wheat, and to assess possible adaptation measures for Bulgarian agriculture under an expected climate change.
Section snippets
Geographic location
Bulgaria is located on the Balkan Peninsula in southeastern Europe. The country includes 31% lowlands (0–200 m), 41% hills (200–600 m), 25% highlands (600–1600 m), and 3% mountains (>1600 m). The Balkan Mountains split the country into northern and southern Bulgaria, and they have a strong effect on the temperature regime. The annual mean air temperatures in Bulgaria vary from −3.0 to 14.0°C, depending on the location and elevation. Air temperature normally reaches a minimum in January, and a
Climate variability
In the initial analysis, long-term variations of air temperature in Bulgaria were investigated. In Fig. 3, anomalies of mean annual air temperature in Bulgaria, relative to the current climatic conditions are presented. Generally, there did not seem to be a significant change in mean annual air temperature in Bulgaria during the 20th century.
The period from the 1920s to 1950s was characterized as a warmer period during the warm-half of the year, i.e. April–September. There has been an obvious
Limitations
Using the observed, e.g. 1961–1990 climate data for creating climate change scenarios, provides spatial and temporal variability. However, it assumes that there is no change in climate variability in the future, compared to current conditions. The created GCM climate change scenarios do not include changes in climate variability, which might represent a very important factor for crop production. An additional limitation of using GCMs is that, although they accurately represent global climate,
Concluding remarks
In this study, we did not find a significant change in the mean annual air temperature in Bulgaria during the 20th century. This is in contrast to the global mean near-surface air temperature, which has increased. Bulgaria has experienced several drought episodes during the 20th century, most notably in the 1940s and 1980s. The mean annual precipitation of Bulgaria has decreased during the 20th century. From the end of the 1970s, we also found a decrease in precipitation during the summer
Acknowledgements
This work was partially supported by a grant from the National Science Foundation/North Atlantic Treaty Organization, State and Federal Funds allocated to Georgia Agricultural Experiment Stations Hatch Project GEO01513, and INCO-Copernicus Project ERBIC 15CT 98 0105.
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