This article was prepared by Gazeta.pl journalist Patryk Strzałkowski.
The meteorological warnings issued on Monday for Warsaw and the surrounding areas proved accurate—first came a strong storm cell, followed by an intense overnight downpour. The consequences could be seen on Tuesday morning on the streets of the capital—some key routes, like a section of the S8 highway, were flooded, with photos showing cars stuck in the water.
When looking at data from weather stations, it becomes clear that flooding was inevitable. According to the Institute of Meteorology and Water Management (IMGW), Warsaw set a new daily rainfall record. Over 90 liters of water fell in 24 hours at the Okęcie measurement station, and nearly 120 liters on the Bielany station. Is that a lot? Yes, indeed—because the average monthly rainfall in July (which is the rainiest month) is about 90 mm or 90 liters per square meter. The average for August is just over 60 mm, so it's fair to say that in Bielany, it rained as much in 24 hours as it typically does in two months.
Drought, drought, downpour—this is how climate change works
The weather situation in Warsaw looks even more dramatic when examining the rainfall chart for the past three weeks. It shows that since the end of July, there was practically no rain at all—something clearly visible in the dried-up lawns and parks. Then came August 19 and 20, and the monthly rainfall norm was not only met but exceeded within hours.
Unfortunately, this kind of downpour doesn't mean that the drought problem can be considered resolved. Such a large amount of water in a short period means that most of it will run off, and if there's no rain again for another week or two, it will become very dry again. Scientists have been warning us about exactly this scenario in connection with climate change.
Global warming isn't just about higher temperatures; it's also about changing weather patterns. This includes changes in precipitation, and according to experts, climate change leads to exactly the kind of scenario we've seen in Warsaw and other parts of Poland. These are prolonged periods without rain, which—especially when combined with high temperatures—can lead to drought. These dry periods are interrupted by such intense rain that it can cause flooding, but only to a limited extent does it help alleviate the drought.
How does climate change lead to stronger downpours? Part of the answer lies in changing weather patterns, and part in basic physics: warmer air can "hold" more water. So, the more we heat the planet by emitting gases from burning oil, coal, and gas, the more water will be in the air—and the stronger the rain will be when that water falls.
For every degree Celsius of climate warming, the atmosphere can hold 7% more moisture, explains NASA. Currently, Earth's climate has warmed by about 1.2 to 1.3 degrees due to our emissions, so the impact on downpours is clear. If we don't eliminate fossil fuels and other sources of emissions, the increase could reach 3 degrees Celsius by the end of this century.
Scientific research confirms that heavy rains are becoming more likely and more intense due to climate change. One such study found that the heavy rain that led to flooding in Ireland last year was twice as likely and 13% more intense due to climate change.
Concrete exacerbates the problem, but greenery alone won't solve everything
Flooding of streets or homes in cities is exacerbated by the fact that most surfaces are impermeable—streets, sidewalks, buildings. Water accumulates there, and the stormwater drainage system is not built to handle such a large amount of rain, leading to flooding.
This effect can be mitigated by greenery and more permeable areas, but it's important to understand their limitations. A green square, meadow, or park will absorb water, unlike a concrete street, but when 40 liters of water fall per square meter in one hour—as was the intensity of the rain in Warsaw—greenery alone won't solve everything, though it can help to some extent.
In some cities—such as Gdańsk—green, natural infrastructure is combined with concrete infrastructure. Rain gardens, a special type of greenery designed to collect rainwater, work in conjunction with the stormwater drainage system. These gardens form the first element in a system for retaining rainwater, followed by the stormwater drainage and large concrete retention tanks.
"Green spaces can store water during heavy rains and hold it for later periods of drought, as well as purify it. Properly designing and maintaining greenery allows for the maximum use of its potential. If we don't go in this direction, flooding and its consequences will only worsen," explained Ryszard Gajewski, president of Gdańskie Wody, which, among other things, creates rain gardens, in an interview with Gazeta.pl.
