Valentin Simeonov has been involved in atmospheric research for more than 40 years, mainly in the areas of air pollution and climate change. He is part of the team at the Swiss Federal Institute of Technology in Lausanne. Water in Bulgaria and how we cope… This is what he shared with FACTS.
- Mr. Simeonov, is it a myth that Bulgaria is rich in water resources?
- Definitely yes. Bulgaria currently has sufficient water resources, but it is not rich, even compared to neighboring countries. The reasons are that there is not much rainfall in Bulgaria. Second, we have no large rivers, glaciers, significant lakes to serve as natural reservoirs of water. Our large lakes Burgas, Varna and Srebarna have relatively small water areas. For comparison, I will give you Switzerland, which has 6% of Europe's water resources, has 1,500 lakes, over 220 dams, and three major European rivers originate and are full-flowing in the country. Despite the availability of these resources for about 10 years, the authorities are preparing the population for a water shortage by the middle of the century. The first signs of a shortage appeared several years ago. For example, there has been a prolonged drought this year in the border areas with France, and some important rivers for water supply have dried up and the authorities have had to distribute bottled water. In general, the problem of water scarcity in Europe - especially in the southern part, is deepening and will become more serious as climate changes progress. This requires us to prepare for this situation from now on.
- What part of the water in our country is suitable for use. What percentage of what Bulgaria has available can be said to be potable?
- Bulgaria has a significant amount of fresh water resources – almost 100 billion cubic meters per year, but this value is misleading, since 75% of it is obtained from the Danube River. However, the Danube waters are not internal, they are polluted and can hardly be used for drinking purposes. In addition, as we have seen in recent years, the river level drops significantly during the summer months, and this trend will worsen as climate change progresses. The remaining 25% of fresh water resources are formed as a result of the balance between precipitation and evaporation. However, Bulgaria is rich in quality mineral waters, which unfortunately are not fully utilized. Water for domestic needs (drinking) is about 5-6% of the total amount of fresh water.
- How is water delivered to cities?
- I mainly deal with climate problems and I will not be very comprehensive in my answer. The main part of water for domestic needs is provided by surface water, mainly dams, rivers and wetlands, the other part is from groundwater. An important role in water supply is played by the water network. In our country, it is outdated, poorly maintained and with water losses of up to 60-70% according to official data. In view of future water shortages, it is important that this network be modernized and losses reduced to the minimum possible, which for developed European countries is a few percent.
- Okay, let's look at things more globally then. How does rising temperature affect the water cycle and the level of the world's oceans?
- This is a very broad question, and here it is good to first give some general information about changes in temperature. In the public space, there is mostly talk about raising the so-called “global temperature”. This increase is more precisely the difference between the average air temperature obtained by averaging all measurements near the earth's surface over a year and the similarly obtained average temperature of the last 50 years of the 19th century. That rise for the early 2020s was about 1.2 degrees, but since late last spring it's been around and above 1.5 degrees every month, and is likely to stay that way for at least a year. An increase of 1.2 and even 1.5 degrees seems insignificant, but these values are misleading.
- Why?
- First, these are average values for the entire Earth, from the poles to the equator. In reality, the increase for Europe is around and above 2 degrees, and for the Arctic it is 5-6 degrees. Second, these are averaged temperatures over a year and include both very cold periods and periods with heat waves where the temperature can exceed 40 degrees, and in some places such as India, some Arab countries and even Turkey, 50 degrees. In addition to the temperature of the air close to the earth's surface, the temperatures of the ocean and the part of the atmosphere that extends to heights of 8 to 15 km also increase. This part is known in science as the troposphere and it is where most of the processes related to weather and climate take place.
- How much is the temperature rising there…
- The temperature in the troposphere is rising at a rate similar to that of the air near the Earth's surface, and the ocean surface temperature in 2023 has risen by about 1.1 degrees compared to the last 50 years of the 19th century. All these temperature changes directly affect the water cycle. Warmer ocean and surface air temperatures increase the release of water vapor from the land surface and ocean. At the same time, the warmer troposphere can absorb a significantly larger amount of water vapor. The maximum amount of water vapor that a kilogram of dry air (about a cubic meter) can absorb increases very quickly with increasing temperature. For example, at zero degrees it is 3.8 grams, at 20 degrees about 15 grams, and at 40 degrees it increases to 49 grams. For these reasons, the amount of water vapor that can return as precipitation increases.
- Is this what these extreme rainfalls we have been witnessing lately are based on?
- This is one of the reasons because more water vapor in the atmosphere means more rain. Another reason is that when water evaporates, it absorbs heat energy, which it then releases to the troposphere. This energy drives the processes responsible for weather and climate. Warming, as we have seen, increases evaporation and adds extra energy to the troposphere, speeding up and amplifying natural processes there. This is also one of the main reasons for the more frequent and strong extreme phenomena such as storms, hail, intense rainfall, hurricane winds, etc. Reduced air pollution due to the deindustrialization of Europe, as well as anti-pollution measures, also contribute to more intense rainfall and more frequent and larger hailstones. This is because cleaner air contains less fine particles and gases such as sulfur dioxide, which play an important role in cloud formation and precipitation. This, along with the greater amount of water vapor, increases the likelihood of extreme precipitation.
- What should we do about air pollution?
- Of course, this is not a reason to stop the fight against air pollution, because it is one of the reasons for increased mortality among people. According to data from the World Health Organization, about 7 million people die annually from dirty air. In addition, air pollution reduces agricultural production and is one of the causes of forest loss. The higher temperatures during the hot periods, the so-called “heat waves”, in turn, lead to a more intense release of water vapor from the earth's surface and vegetation, which is one of the causes of seasonal droughts. Or briefly we can summarize that the increase in the Earth's temperature leads to both extreme rainfall and severe droughts. An important element of the water cycle is its storage in the so-called “natural reservoirs“. These reservoirs store water from rainfall and release it gradually, compensating to some extent for unevenness or lack of rainfall. A very important natural reservoir are those parts of the earth's surface that are covered with snow and ice. In temperate latitudes, the amount of water stored in them increases during the cold seasons and is gradually released during the warm ones. As climate change progresses, the ability of this reservoir to store water decreases because both the thickness and duration of snowpack periods and the number and amount of water stored in mountain glaciers decrease.
- It snowed twice in Sofia this winter…
- And not only in Sofia, but in all of Europe and the world in general. Other important natural reservoirs are groundwater and surface water such as rivers, lakes, marshes and wetlands. . Their ability to store water is declining not only because of climate change, but also because of overuse and pollution, reducing their ability to be used by humans.
- What to expect if we can summarize. More and more warm weather, more and more drought…
- Not only. More extreme events, more heavy rainfall, large hail, more frequent and longer periods of drought, greater likelihood of wildfires. Finally, I would like to comment on the important role of vegetation and especially forests in the water cycle and the special role of forests in Bulgaria, since the main part of the precipitation in our country falls over mountainous (forest) areas.
Forests are an important local source of water vapor because, through a natural process called transpiration, they extract water and nutrients from the deeper layers of the soil and evaporate much of it through their aerial parts, mainly the leaves. The amount of water evaporated is impressive. A large oak tree, for example, can evaporate up to 150 cubic meters of water per year. This amount increases during hot periods as the plants are cooled in this way. The released water vapor rises quickly because it is lighter than air, and is replaced by air masses from more distant areas, which can often carry additional moisture. Forests also release substances and fine particles that help form and precipitate local clouds.
Forests also play an important role in the formation and retention of groundwater. They slow down and evenly distribute the incoming rainwater along the road and to the soil. In addition to the complex root system, the forest soil is also rich in various forms of life such as microorganisms, insects, fungi, which make it permeable and allow the storage of large amounts of water. This water can be released gradually, constantly feeding the rivers springing from the forest massifs.
However, forests both in our country and worldwide are decreasing due to logging and forest fires. Due to climate change, fires are becoming a major threat to them, as the periods in which they are possible, their scale and strength are increasing every year.
And in closing, if you have to remember anything from what we've talked about so far, it's that we have to protect the forests, because - if we run out of forests, we run out of water.