century and their connection to soil droughtsmeteorology.meteo.bg/soil_drought_12_ENG.pdf · 2014-05-28 · Weather scenarios for the 21st century and their connection to soil droughts

Weather scenarios for the 21st century and their connection to soil droughts

INTRODUCTION Humanity will always be at risk from unexpected and unfavourable climate changes caused by natural terrestrial or cosmic phenomena. The cosmic factors include the solar activity and the parameters of the earth’s orbit. The terrestrial factors include, for example, shifting of the earth’s poles, changes of the speed of the Earth’s rotation and changes of the Earth’s physical and geographical appearance (such as changes in the configuration of continents, changes in the level of the global ocean, formation of mountain massifs, etc.). The natural factors influence the general atmospheric circulation, the oceanic flows and the cryosphere and, thus, the climate and its fluctuations and changes. The difference between the distant and near past is that now the risk exists of rapid man-caused climate changes. Most scientists believe that the emissions of carbon dioxide (CO2) and of other gases known as greenhouse gases, released into the atmosphere mainly from the industry and agriculture can cause irreversible climate changes.

Life on Earth as we know it is possible because of the natural greenhouse effect. This phenomenon maintains our planet sufficiently warm for the proper functioning of all living organisms. Ever since life had started for the first time, the emitting of natural greenhouse gasses has been helping to maintain the Earth’s temperature within life-supporting limits. If there were no greenhouse effect, the planet’s average temperatures would be so low that life would not be possible. The absence of greenhouse gasses would reduce the Earth’s temperature by about 33°C, rendering it yet another lifeless planet of the solar system. The issue of the increased greenhouse effects and the global warming related to it had been to the forefront of the thinking of researchers, the media and the decision makers. Our planet’s climate is constantly changing, but if these changes had occurred naturally in the past, now most scientists believe that the emissions of carbon dioxide (CO2) and of other gases known as greenhouse gases, released into the atmosphere mainly from the industry and agriculture can cause irreversible climate changes. The climate changes presuppose a global climate change and transition toward a new state of equilibrium causing regional and local changes. According to the Framework Climate Change Directive of the UN (UNCCD) of 1992, climate change means a change of climate which is attributed directly to human activity, alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods.

The increased concentrations of carbon dioxide and of the other atmospheric gases involved in the greenhouse effect can cause substantial changes to the Earth’s radiation balance by absorbing the long-wave radiation directed toward outer space and re-emitting it toward the Earth’s surface and increase air temperature near the surface. The concentration of carbon dioxide in the atmosphere has increased by approximately 31% since 1750 as the result of incineration of solid fuels, gasses, forest felling etc. The emissions of greenhouse gasses have continued to change the composition of the atmosphere early in the 21st century and, therefore, the Earth’s climate.

EMISSION SCENARIOS The mathematical climate models used to simulate the expected climate changes during the 21st century need scenarios of future emissions, greenhouses and aerosols in the atmosphere. These emission scenarios are needed to model and analyse the expected global climate changes while taking into account the greenhouse effect and of the effect of atmospheric aerosol concentrations to increase radiation. The Intergovernmental Panel on Climate Change, IPCC, has developed a number

of emission scenarios, the most recent group of scenarios, SRES1, being published at the end of the past century.

This group of emission scenarios comprises four main types of scenarios (A1, B1, A2 and B2, described in detail in the Appendix), grouped on their own part into additional emission scenarios. The total number of emission scenarios is 40, with 35 containing the full range of greenhouse gasses into the atmosphere and being used as input information for the climate models. These scenarios describe broadly the main demographic, economic and technological sources that affect, and will continue to affect, the future greenhouse gas and aerosol emissions into the atmosphere.

The A2 scenarios depict a very heterogenic world with preserved local identity. In these scenarios, regarded as the slowest in comparison to the three other types of scenarios, the global population is constantly increasing, economic development is markedly regional, and different regions feature different changes of DGP and of technology. These scenarios are regarded as the most realistic ones and are most widely used in many scientific studies.

CLIMATE MODELS Anthropogenic influence will continue to change the composition of the atmosphere throughout the 21st century. Global climate models (GCM) are used in order to assess the future concentrations of greenhouse gasses and atmospheric aerosols and their influence on the expected climate. These models simulate the physical, chemical and biological processes and interactions of the system atmosphere-oceans-land surface. The global climate models calculate the frames of the future climate using measured and potential future greenhouse gasses and atmospheric aerosols. Therefore, the climate models use as their input data about the existing as well as expected warming due to the already registered emissions of the respective greenhouse gas and aerosols. However, we should be referring to climate scenarios and not climate forecasts as the proposals related to future climate conditions are based also on the SRES emission scenarios for greenhouse gasses and atmospheric aerosols.

There are perhaps more than 20 centres worldwide involved in global and regional climate modelling. Some of these are the Max Plank Institute of Meteorology (Germany), the Hadley Centre for Climate Forecasts and Studies (Great Britain), the Canadian Climate Centre, the Australian model centre CSIRO, the Geophysical Fluid Dynamics Laboratory (USA) and many others (IPPC, 2001).

One of the main problems in applying the climate scenarios simulated by the global climate models is related to the so-called “regionalisation” or “scaling” toward a higher spatial resolution. There are several methods for scaling of climate scenarios comprising four main groups: use of values from the nearest point in the grid of the global climate models; interpolation of the values from the nearest 4 points in the grid of the global climate models; scaling using statistical models; regionalisation by inclusion of additional simulations using regional climate models. The first method is least accurate, while the others have both positive and negative features (IPCC-TGCIA, 1999).

1 Special Report on Emission Scenarios

CLIMATE SCENARIOS FOR THE 21ST CENTURY – GLOBAL, EUROPEAN AND FOR THE BALKAN PENINSULA

The global scale The global climate models simulate an increase of the average global temperature at the ground layer from 1.4 to 5.8°C by the end of the 21st century, as compared to 1990. This result includes the full range of the SRES emission scenarios and the calculations from a number of global climate models. The expected degree of global warming is much higher than the observed increase of global temperature during the 20th century. The projected global warming is considered, based on paleoclimatic information, to have no analogue in the past, or at least during the past 10,000 years. The results from the global climate models show that the average global concentration of water steam and the global precipitation will perhaps increase during the 21st century. Precipitation is expected to increase, by the end of the century, in the medium high and high latitudes of the Northern Hemisphere and above the Antarctic during the winter. Increasing precipitation is expected in the low latitudes in some regions, while in other low-lying areas precipitation will be limited. Wider precipitation fluctuations are expected each year during the 21st century over the areas with increased precipitation totals as compared to the totals typical of the contemporary climate2. Also, attention should be paid to the potential future change of extreme weather events and disasters, such as the following: floods and dry spells, forest fires, storms, hurricanes etc. Especially since the trend is that the natural disasters will become more frequent. The model results and expert assessments show that the future climate will feature higher maximum air temperatures, due to which there will be more hot days above significant terrestrial areas. The minimum air temperatures will also be exceeded during the 21st century, with fewer cold days and days with frost. Therefore, the day and night amplitude of the air temperatures will continue to decrease in the future. The weather events with intensive precipitation (such as floods, landslides etc.) are expected to become more frequent. On the other hand, it is likely that the summertime droughts over the continental mean geographic latitudes will become more frequent. The number of tropical cyclones with higher wind and precipitation peaks is also expected to increase.

The European scale The model climate scenarios project an increase in the average annual air temperature in Europe from 0.1 to 0.4°C in one decade. The warming will be more significant in Southern Europe and in North-eastern Europe, and will be least significant along the Atlantic coastline of the continent. The continental interior of Eastern Europe and Western Russia will become warmer more quickly during the winter. The expected warming during the summer shows a significant parallel warming gradient, with Southern Europe becoming warmer by 0.2 to 0.6°C per decade, while warming in Nortner Europe becoming warmer by 0.08 to 0.3°C in one decade. The winters classified within the contemporary climate period as cold will be observed less frequently during the 2020-ies and will most likely disappear completely during the 2080-ies. In contrast, hot summers will occur more often and almost all summers during the 2080-ies are expected to be hot. It is important to point out that some weather models simulate scenarios where the regional and seasonal climate changes differ from those described above. The annual precipitation over Europe will increase in the regions of Northern Europe (between +1 and +2% per decade), and will decrease in Southern Europe, changing slightly or more significantly in Central Europe. The changes of wintertime and summertime precipitation are expected to be in significant contrast. Most of the continent will receive higher quantities of precipitation during the winter. Significant differences between the

2 The so-called “contemporary climate” spans, according to the World Meteorological Organization, the period 1961-1990. The next contemporary climate will be introduced in 2021, i.e. it will span the period 1991-2020.

changes of precipitation in Northern Europe (an increase of +2% per decade) and in Eastern Europe (reduction by approximately 5% per decade) are expected during the summer.

The Balkan Peninsula The climate scenarios for the 2050-ies in the Balkan Peninsula, simulated by the German Climate Model ECHAM4, show a lower degree of warming in Southern Greece, South-eastern Rumania, Eastern Bulgaria and North-western Turkey (Figure 1). Annual air temperatures between 2.0 and 2.5oC are expected in the remaining areas of the Balkan Peninsula by the middle of the 21st century. The annual precipitation totals will decrease in this area of South-eastern Europe, as predicted by most of the models. The precipitation quantities projected by the ECHAM4 model to decrease will vary between 5 and 10% over the same time period (the 2050-ies) in the southern and southeastern areas of the Balkan Peninsula.

Despite some lack of clarity regarding future precipitation, most climate models simulate increased wintertime precipitation and reduced precipitation during the warm half of the year in South-eastern Europe and the Balkan Peninsula in the 21st century.

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Figure 1. Climate scenarios by ECHAM4 GCM for the average annual air temperature (a) and the annual precipitation totals (b) in Europe during the 2050-ies (emission scenario A2 SRES),

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Температура (оС) Figure 2. Climate model scenarios for average air temperature and precipitation during the summer in Serbia and Montenegro (a), Romania (b), Greece (c) and Turkey (d) by the end of the 21st century

(emission scenario A2 SRES), as compared to the current climate (1961-1990)

CLIMATE SCENARIOS FOR BULGARIA

Climate scenarios for the end of the 21st century Some climate models simulate increased air temperatures in Bulgaria by 2 to 5°C with doubled concentration of carbon dioxide in air.

Most climate scenarios project an increase in winter precipitation in Bulgaria by the end of this century, but precipitation during the warm half of the year, mainly during the summer, is expected to decrease significantly (Figure 3).

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Figure 3. Climate model scenarios for the average air temperature and precipitation in the winter (a, c) and in the summer (b, d) in Bulgaria by the end of the 21st century (for the A2 (a, b) and B2 (c, d)

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Climate scenarios for different periods during the 21st century

Climate scenarios for the 2020-ies, 2050-ies and the 2080-ies As a general rule, the modern climate (1961-1990), simulated by GCMs, should be compared initially to the current climate conditions of a region, and not to the climate in a specific station. It is not realistic to expect that a relatively large grid network can present the climate well in a station (ANL, 1994). Therefore, the average values of weather elements in a region should be used.

Based on regional comparisons of the simulated and observed climate shown in Table 1, the HadCM2 model was determined as the most suitable GCM model, simulating air temperatures in Bulgaria. The differences between the measured and calculated monthly temperatures exceed 2°C only in April, May and June. The GFDL-R15 model also provided a good simulation of the monthly air temperatures for the period September through February (Table 1).

Table 1. Deviations of the GCM simulated air temperatures T (°C) and precipitation P (%) in Bulgaria, as compared to their measured values for the modern climate period (1961-1990).

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I II III IV V VI VII VIII IX X XI XII T 5.3 3.4 1.2 -0.9 -1.8 -1.3 -0.4 0.5 1.3 2.5 3.4 4.6

ECHAM4 P 88 56 89 12 -27 -40 -32 -55 -4 79 67 89 T 1.6 0.6 -0.7 -2.8 -3.1 -2.3 -0.3 0.5 -1.0 -0.6 0.0 0.6

HadCM2 P 59 55 72 29 32 11 -25 -22 -2 18 52 34 T 5.1 3.7 1.7 -0.1 0 1.8 4.2 4.9 2.9 1.9 1.3 3.6

CGCM1 P 19 3 21 -10 -32 -54 -70 -83 -65 -16 -25 5 T 3.4 2.3 1.2 -1.0 -1.3 -0.9 -0.4 0.3 0.2 0.8 1.6 2.5

CSIRO-Mk2b P 58 51 47 10 -8 -15 -4 -5 5 46 4 50 T -0.4 -1.2 -3.1 -4.6 -4.7 -2.3 0.1 2.7 0.8 -0.8 -1.2 -1.6

GFDL-R15 P 51 56 89 78 25 -42 -67 -78 -33 72 79 57

In this case most GCM models, except for CGCM1, simulated higher average precipitation values for Bulgaria during the cold half of the year. On the other hand, the simulated precipitation during the summer period is lower than the measured average precipitation. This is particularly true of the models CGCM1 and GFDL-R15. The SIRO-Mk2b model simulated well the measured precipitation between April and September, as well as in November, with deviations below 15%. The remaining GCMs tend to “overestimate” or “underestimate” precipitation in most months of the year by a wide margin.

The GCM simulation results show an increase in annual air temperatures in Bulgaria between 0.7 (HadCM2) and 1.8°C (GFDL-R15) during the 2020-ies. The HadCM2 model even simulated a slight drop in temperatures in November. Warmer climate is expected during the 2050-ies and 2080-ies, with increased air temperatures from 1.6 (HadCM2) to 3.1°C (GFDL-R15) during the 2050-ies and from 2.9 (HadCM2 and CGCM) to 4.1°C (ECHAM4) during the 2080-ies. More significant warming is expected during the summer of the 2080-ies (Figure 4).

The CGCM1 model predicted an increase in annual precipitation during the 2020-ies and 2050-ies. However, the GFDL-R15 model projected a decreased monthly precipitation in May, June and July. The models ECHAM4, HadCM2 and CSIRO-Mk2b simulated a reduction in the monthly, seasonal and annual precipitation during the 2080-ies. The change in monthly solar radiation is expected to

vary between -10 and 10% during the 21st century. Increased solar radiation was shown also by the ECHAM4 model.

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Figure 4. GCM climate scenarios for monthly temperature (a, c, e) and precipitation (b, d, f) in

Bulgaria during the 2020-ies (a, b), 2050-ies (c, d) and 2080-ies (e, f)

Climate scenarios for the 2025-s, 2050-ies and the 2100-s The HadCM2 and ECHAM4 models predicted that the average annual air temperatures in selected areas in Northern Bulgaria (along the Osam River) and Southern Bulgaria (along the Struma River) is likely to increase by, respectively, 0.9 and 1.0 and by 1.1 and 1.3oC during the 2025-s (Figure 5). The HadCM2 model projected the following increases in seasonal air temperature: 1.0oC (winter), 0.6oC (spring), 1.2oC (summer) and 0.9oC (autumn) (Figure 6). For its own part, the ECHAM4 model simulated an increase in seasonal air temperature, which are close to, or higher than, 1.0°C: 1.0oC (winter), 1.1oC (spring), 1.4oC (summer) and 1.2oC (summer). Naturally, a warmer climate is expected by the middle of the 21st century (2050-ies) and by the end of the century, when the average annual temperatures are likely to increase from 1.6 - 1.8 (HadCM2) to 2.1-2.2°C (ECHAM4) during the 2050-ies, and between 3.3-3.5 (HadCM2) and 4.2-4.3°C (ECHAM4) during the 2010-s (Figure 6). According to the HadCM2 model, warming will be more tangible during the

winter and especially during the summer months of the 2050-ies and 2100-s (Figures 5 and 6). The ECHAM4 model also simulated a tangible warming during the summer period (June-August).

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Figure 6. Seasonal and annual climate scenarios for air temperatures (a, c, e) and precipitation (b, d, f) in the town of Sandanski (along the Struma River), simulated by the climate models HaDCM2

and ECHAM4 for the 2025-s (a, b), 2050-ies (c, d) and the 2100-s (e, f)

Both models, HadCM2 and ECHAM4 simulated a reduction of the annual precipitation totals in the respective regions under consideration (Figures 5 and 6). This applies particularly well to the HadCM2 model, which simulated a decrease in precipitation during all months of the year (Figure 5). For its own part, the ECHAM4 model forecasted an increase in the current precipitation levels (1961-1990) only during the months of August and December. The HadCM2 and ECHAM4 models simulated an average reduction by 3-5% and, respectively, 2-3% for the annual precipitation totals in the 2025-s, as compared to the modern climate standards (1961-1990). The reduction in annual precipitation is expected to continue through the 2050-s and the 2100-s: 6-9% (HadCM2) and 4-5%

(ECHAM4) for the half of this century and between 12-18% (HadCM2) and 8-10% (ECHAM4) by the end of the 21st century. The precipitation reduction simulated by HaDCM2 is expected to be more significant in July and August (Figure 5), especially in the 2100-s. This is why the HadCM2 model simulated a higher-than 30% precipitation drop during the summer period (Figure 6).

The climate models were applied to the climate standards for the period 1961-1990 for various weather stations throughout Bulgaria. For example, figures 7 and 8 present the monthly, seasonal and annual climate values of air temperature and precipitation in 4 stations in the weather scenarios for the 21st century, simulated by the HaDCM2 and ECHAM4 models.

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Figure 7. Monthly climate values for air temperature (a, c, e) and precipitation (b, d, f) in Petrich and Nikolaevo, according to the HaDCM2 climate scenarios for 2025-s (a, b), 2050-ies (c, d) and

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DJF MAM JJA SON Annual Figure 8. Seasonal and annual climate scenarios for air temperatures (a, c, e) and precipitation (b, d, f) in the town of Sandanski and Troyan, simulated by the climate models ECHAM4 for the 2025-s

(a, b), 2050-ies (c, d) and the 2100-s (e, f)

The local air temperature in January in Nikolaevo is expected to remain negative during the 2025-s. However, by the end of the 21st century, the monthly temperature during the same month is likely to be positive (Figure 7). The air temperature in Petrich during July and August would reach 30oC by the end of this century. The monthly precipitation in the same station is likely to be at a low in August and September, at about 20 mm during the 2100-s.

The seasonal precipitation during the winter and the autumn will remain almost the same in Blagoevgrad and Troyan during this century (Figure 8). However, the precipitation totals in Troyan during the spring are expected to remain more significant in comparison to Blagoevgrad. For this

reason, the difference in annual precipitation for those 2 stations will remain higher than 100 mm in the future.

Climate scenarios for 2020, 2050 amd 2080 There are at least 3 main centres in Europe involved in global climate modelling: the Max Plank Institute of Meteorology (Germany); the Hadley Centre for Climate Forecasts and Studies (Great Britain); the French Meteorological Service etc. The climate scenarios for Bulgaria in this and the following sections were obtained from simulations with the English model HadCM3 of the Hadley Centre for Climate Forecasts and Studies. An A2 SRES emission scenario was used. This model and this emission scenario were used for the following reasons:

• the HadCM3 model is believed (although with some degree of subjectivism) to give a comparatively good description of Europe’s climate and of Bulgaria

• the HadCM3 version was prepared, improved and implemented on modern powerful computers relatively recently

• the data base of HadCM3 climate scenarios for Europe (and Bulgaria) had a very high spatial resolution: 10’ latitude х 10’ longitude (approximately 18 km x 18 km at the equator). The high spatial density of the grid network of HadCM3 climate scenarios was achieved by preliminary application (by the Institute for Climate Influences, Potsdam, Germany) of a “thin-plate smoothing splines” (New et al., 2002) – a type of interpolation using the altitude, latitude and longitude as independent predicators.

• the A2 emission scenarios are regarded as the most realistic emission scenarios and are most widely used in many scientific studies.

• The combination of HadCM3 and A2 model climate scenarios (Figure 9) has been used during the past/current years in a series of EC funded scientific studies of the effect of climate change on various sectors (water resources, lands and forests, human health etc.).

Figure 10 presents the climate scenarios for the monthly air temperatures and the precipitation in Novachene (Northern Bulgaria), consistent with the simulations of the HaDCM3 model for the years 2020, 2050 and 2080. It can be seen that this version (HadCM3) of the English model simulated a higher increase of the monthly air temperatures as compared to the increase generated from the previous version (HadCM2) of this model. Even the air temperature in Novachene in July and August is expected to be nearly 8oC higher than the temperature typical for the period of the modern climate (1961-1990). The simulated HadCM3 precipitation follows almost the same orientation during the 21st century as that modelled by the HadCM2 and ECHAM4 models – a decrease. The monthly precipitation in Novachene between May and September are expected to fall by 50% in 2080. Only the precipitation in February, March and December are likely to increase during the 21st century.

HadCM3 climate scenarios were created for various regions in Bulgaria. An example about South-eastern Bulgaria is presented on Figure 11. The simulation increase of monthly air temperatures in 2020 in Elhovo is lower than 2°C. A significant warming is expected to occur during the summer months of 2080. The air temperature is also expected to increase in July and August by approximately 7-8°C by the end of the 21st century in one emission scenario, especially during the warm half of the year. The HadCM3 model simulated a slight increase of precipitation in South-eastern Bulgaria during the 21st century (2020, 2050 and 2080) only in March. The most significant drop in precipitation (> 70%) in Elhovo was simulated for July 2080.

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Figure 9. Changes of summer temperatures (a) and precipitation (b) in Europe simulated by the HadCM3 and PCM models for 2080; A2 SRES emission scenario

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Novachene for 2020, 2050 and 2080, as compared to the period 1961-1990.

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8.0

ΔT (o

C)

202020502080

a)

1 2 3 4 5 6 7 8 9 10 11 12

Month

-80

-60

-40

-20

0

20ΔP

(%)202020502080a)

Figure 11. HaDCM3 climate scenarios for the monthly air temperature (a) and precipitation (b) in

Elhovo for 2020, 2050 and 2080, as compared to the period 1961-1990.

Climate scenarios for 2015 The HadCM3 A2 climate3 scenarios for 2015 for four regions in Bulgaria (Northern Bulgaria, Eastern Bulgaria, the Thracian valley, and South-eastern Bulgaria) are presented in Table 1. The increase in average annual air temperature in 2015 as compared to the modern climate standard (1961-1990) is expected to be between 0.7 (in Eastern Bulgaria) and 1.1оС (in the remaining regions of Bulgaria). However, the warming within the year is different in different seasons and months. Perhaps warming will be more pronounced during the summer months (July, August and September) and will be less pronounced during the cold half of the year. Even the HadCM3 model simulated lower monthly temperatures for November (compared to the climate standard): -0.2оC in Southwestern Bulgaria and in Northern Bulgaria, and -0.6оC in Eastern Bulgaria. The temperatures in February may not increase in Eastern Bulgaria until 2015, and the summer months will, perhaps, not be as hot as in other areas of Bulgaria.

Regardless of the complexity of simulation of future precipitation and of the specifics of this hydro meteorological element, here is the possible HadCM3 A2 scenario: precipitation during some

3 these scenarios do not consider the fluctuation of weather elements from one year to the next

months (such as May, July and September) is expected to decrease during the warm half of the year by approximately 30% of the present (1961-1990) climate standards. This will increase the risk of drought – increased frequency of occurrence, intensity and degree of impact. Perhaps this may not sound serious in the year (2005) in which Bulgaria is being affected by a series of floods caused by significant and intensive precipitation. However, it is believed that each relatively wet period is followed by a dry period. This statement is proven by the analyses of available hydro meteorological information from the end of the 19th century until, and including, 2004. The droughts have been and will be part of the weather cycle in the Balkan Peninsula and in Bulgaria. The drop in precipitation, calculated by HadCM3 A2 for the cold half of the year, is significantly lower (Table 2). A slight increase in monthly precipitation quantities is projected even for South-eastern Bulgaria during December, March and, particularly, November (by 20%). The percentage changes of precipitation totals in the Thracian valley March and November are also low, although positive.

Table 2. Changes of the mean monthly air temperature (°C) and monthly precipitation (%) in 2015 in individual regions in Bulgaria as compared to the climate standards for the modern climate period (1961-;-1990) HadCM3 A2 climate scenarios.

Northern Bulgaria Eastern Bulgaria The Thracian valley South-western Bulgaria

Month temp (oC)

Precipitation (%)

temp (oC)

Precipitation (%)

temp (oC)

Precipitation (%)

temp (oC)

Precipitation (%)

I 1.4 -9 1.2 -22 1.2 -8 0.8 -11

II 0.2 -6 -0.1 -17 0.3 -9 0.0 -8

III 1.0 2 0.3 -12 1.1 5 1.2 2

IV 0.7 -5 0.2 -11 1.1 -11 1.2 -4

V 1.0 -31 0.4 -32 0.8 -35 1.0 -39

VI 1.1 -13 0.9 -10 1.2 -14 0.9 -10

VII 1.9 -28 1.5 -31 1.9 -35 2.2 -30

VIII 1.9 -19 1.3 -39 1.8 -12 2.2 -6

IX 1.8 -30 1.3 -22 1.9 -29 1.9 -29

X 0.9 -9 0.5 2 0.8 -18 0.9 -16

XI -0.2 -5 -0.6 -4 0.0 4 -0.2 20

XII 1.3 -2 1.0 -2 1.1 -3 0.7 2

THE CLIMATE CHANGES AND THEIR RELATION TO SOIL DROUGHT IN BULGARIA It can be seen from the above results that Bulgaria is to expect warming and reduction of the precipitation quantities, especially during the warm half of the year. The declining precipitation totals will cause a change of the water resources. For example, the river flows will decrease by 40-50%, provided that the most pessimistic scenarios come true in the future (Alexandrov and Genev, 2004, for example). The high air temperatures combined with the precipitation deficit of the summer season will lead to higher transpiration and evapotranspiration values during this time of year. All this will increase the risk of all types of drought – atmospheric, soil, soil-atmospheric, hydrological, and even socio-economic. The opponents of this proposition will most likely resort to the torrential precipitation and serious floods in 2005. However, we should not forget the year 2000

which is not that far back into the past, when Bulgaria was affected by a tangible drought. Which, perhaps, is a confirmation of the trend of the recent years for increased frequency of extreme natural phenomena, including floods and dry spells. What is more, it will be noted once again that each relatively wet period is followed by a relatively dry period. One proof is in the analyses and the results from the available hydro meteorological information from the end of the 19th century until the present day. The droughts have been and will be part of the weather cycle in the Balkan Peninsula and in Bulgaria.

As regards soil drought: the following negative impacts can be added to the negative effect of reduced precipitation during the warm half of the year, the expected drop in river flows and the increased transpiration and evapotranspiration:

• Increased consumption of groundwater due to exhaustion of the moisture in the surface soil layer, as is seen from the simulated precipitation deficit during the warm half of the year;

• Felling of forests and destruction of forest massifs, provided that the trend of indiscriminate felling of the past 10-15 years continues and becomes even worse in the future. This will reduce the soil humidity naturally accumulated in the forest areas;

• Increased risk of dry winds due to warming, reduced precipitation and changed occurrence, i.e. more intensive precipitation combined with longer dry spells. In the case of dry winds, the upper soil layer dries up and increases soil drought;

• Land-use changes – changes of soil properties due to warming, moisture deficit, increased transpiration, decreased soil humidity, change of drainage, etc. Increased soil erosion is possible, especially in agricultural areas where soil erosion occurs also in the conditions of the modern climate.

The above leads to the following logical conclusion: the climate scenarios indicate that higher risks of soil drought are to be expected – increased frequency of occurrence, intensity and impact of soil droughts during the 21st century in Bulgaria. Most vulnerable to these changes will be the soils with low water retention capacity, and the regions in South-eastern Bulgaria, where precipitation during the warm half of the year are low, even in the current climate conditions.

REFERENCES

1. Alexandrov, V. and M.Genev, 2004. The effect of climate variability and change on water resources in Bulgaria. In: Webb, B., N.Arnell, C.Onof, N.Maclntyre, R. Gurney and C.Kirby. Hydrology: Science and Practice for the 21st century. British Hydrological Society, Vol. 1, pp.1-8.

2. Argonne National Laboratory (ANL). (1994). Guidance for Vulnerability and Adaptation assessments. U.S. Country Studies Program, Washington D.C., USA, 205 pp.

3. Intergovernmental Panel on Climate Change (IPCC), 2001. Climate Change 2001: The Scientific Basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell, and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

4. Intergovernmental Panel on Climate Change – Task Group on Scenarios for Climate Impact Assessment (IPCC-TGCIA), 1999. Guidelines on the Use of Scenario Data for Climate Impact and Adaptation Assessment, IPCC, 69 p.

5. New, M, D. Lister, Mike Hulme and I Makin, 2002. A high-resolution data set of surface climate over global land areas. Clim Res 21: 1–25

ANNEX The A1 scenarios describe a future world with rapid economic growth: global population increasing until the middle of the 21st century, with subsequent decreasing, and intensive introduction of new and more efficient technologies; approximation of the social and economic condition of individual regions; interaction and cooperation between individual cultural and social communities; significant reduction of regional differences in gross domestic product per capita; The A1 scenarios establish three main lines of development related to technological changes in the energy sector: energy resources based on intensive use of solid fuel (A1FI scenarios); energy resources that do not include solid fuel (A1T scenarios); or a balance between individual energy resources (A1B).

The A2 scenarios depict a very heterogenic world with preserved local identity. In these scenarios, regarded as the slowest in comparison to the three other types of scenarios, the global population is constantly increasing, economic development is markedly regional, and different regions feature different changes of DGP and of technology.

The B1 scenarios concern a converging world with global population identical to that of the A1 scenarios. These scenarios feature rapid growth of economic structures; introduction of environmentally clean and efficient technologies; marked global solutions leading to sustainable socio-economic development and environment, but not including any additional climate-related initiatives.

For their own part, the B2 scenarios outline a world where the solutions for sustainable social and economic development are taken mainly at the local level. This is a world with a constantly growing population (but at a slower rate than that in the A2 scenarios); average level of economic growth; slower and more diverse technological changes as compared to the A1 and B1 scenarios. The B2 scenarios are also aimed to preserve the environment and the social prosperity, but they also focus upon the local and regional levels.

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century and their connection to soil droughtsmeteorology.meteo.bg/soil_drought_12_ENG.pdf · 2014-05-28 · Weather scenarios for the 21st century and their connection to soil droughts