The cause of the flood in Istanbul dates back 42 years! 6 times greater flood impact on concrete: 'It is obvious from the name of the region'

Zeynep Dilara Akyürek / Milliyet.com.tr – The rains, which are expected to last until Friday in Istanbul, caused heavy damage, loss of life and property in many points, especially in Ayazağa and Kağıthane. Search and rescue teams work hard in a 'natural disaster' where roads collapse, landslides occur and buildings are completely flooded. Search and rescue activities continue in the 36th hour of the rain. Many people ask the same question about the flood disaster in Istanbul: Is the cause of the disaster only rainfall? Prof. from ITU Climate Science and Meteorological Engineering Department. Dr. Mikdat Kadıoğlu told Milliyet.com.tr about the steps that started 42 years ago and lie at the basis of what is happening today, the cause of the flood and the disasters that impermeable surfaces can cause.

When we talk about many disasters, we add the word 'natural' to them. However, sometimes when it is natural, nature does not turn precipitation into a disaster anyway. In other words, while we do not see a flood in the forests, we are talking about a flood in parks, settlements and roads. At this point, while nature strives to take back what belongs to it, humanity resists. Prof. Dr. Mikdat Kadıoğlu evaluated yesterday's rainfall according to regions where land areas are large and urbanization is intense. Prof. Dr. Kadıoğlu explains the difference in impact between the two regions: "As MGM (General Directorate of Meteorology) stated in its previous analysis, the greatest damage was always suffered by the settlements, factories, highways and bridges near the stream beds. The waterway could not be found; it found people, vehicles and buildings in its path. Yesterday, the biggest rainfall fell on the northern slopes, Beykoz, Sarıyer, Eyüpsultan, most of which are still covered with forest. The soil retained some of the water. Our losses are due to the water entering the construction again. "It happened in places: the bus that was dragged in Ayazağa, the flooded underpasses, the subway station, the hospital. And our lost child died in a street where water and electricity meet. Flood is not about how many layers of rain there are, but whether the water can flow and find its way. If the same rain falls on a forest, it is rain, if it falls on an industrial site in the stream bed, it is a disaster," he explained. So, is Megakant, covered with impermeable surfaces that turn precipitation into floods, the very reason for this? Prof. Dr. Mikdat Kadıoğlu explained how the size of the flood changes when the same amount of rain falls on the forest and concrete:

"1 millimeter of precipitation falling on one square meter is 1 liter, that is, 1 kilogram of water. When yesterday's 230 kilograms of precipitation falls on the forest, only 10 to 20 percent of it flows from the surface, according to typical runoff coefficients used in engineering; the rest infiltrates the soil and is retained in the trees and leaf cover. When the same precipitation falls on asphalt and concrete, 80 to 95 percent returns to surface runoff within minutes. In other words, the same rain produces floods in concrete approximately 6 times as much as in the forest. A While approximately 35 thousand tons of 230 millimeters of precipitation flows in a square kilometer of forest, approximately 207 thousand tons of water in a square kilometer of concrete searches for the lowest point, that is, the stream bed, underpass and basement. Instead of looking at the sky and asking, 'How many times is this rainfall?', we should look at the ground and ask, 'How many times has our concrete increased?'

Permeable surface means large green areas, natural areas consisting of soil pieces and stones. If it is necessary to settle in these areas and the region presents a dangerous picture in terms of floods, permeable surfaces and sponge cities should be adopted. However, reinforced concrete and vertical urbanization often do not allow this. As the amount of concrete increases, the risk of flood increases. Istanbul, in particular, is one of the world's largest cities and one of the most crowded living spots. The megacity, whose population is increasing day by day, is being equipped with new housing projects and living centers. Over time, this causes the settlement to overflow to points where it should remain as a stream. What emerges at the end is floods and floods on impermeable surfaces! So how many times have waterproof surfaces increased in Istanbul in the last 10 years?

"Here is the real problem: There is no official and up-to-date answer to this question. Istanbul does not measure and publish the amount of its impermeable surface every year. We only have signs given by scientific studies piece by piece, and they all point in the same direction: According to the study conducted by Sarı and Musaoğlu (2023) with satellite images, the impermeable surfaces in Istanbul's Northern Forests increased by 221 percent, that is, 3.2 times, between 1984 and 2017; only It increased by 63 percent in the eight years between 2009 and 2017. According to a study cited by Çiğerci et al. (2024), approximately 16 thousand 500 hectares (165 square kilometers) of land were converted into settlements or large construction projects in the four years between 2013 and 2017. Therefore, my suggestion is clear: IMM and Environment. "The Ministry of Urbanization and Climate Change should calculate the increase in impermeable surface in Istanbul's district and stream basin in the last 10 years with satellite data and announce it to the public every year. If the rate of concrete in a basin increases and the capacity of the stream, grate and underpass in that basin remains the same, the address of the next flood is clear. We count the building stock for the earthquake; we should also count the concrete for the flood." - Prof. Dr. Mikdat Kadıoğlu

Major flood disasters have occurred in many provinces of our country before, and local governments and the Ministry of Environment, Urbanization and Climate Change ensured that the damaged settlements were repaired. However, the lost people could not be brought back, and errors and deficiencies in city planning caused the most terrible scenes to emerge here. The damage suffered today in places with words such as 'valley, stream, lake' in their names revealed this. Because these names were not given to these places for analogy. These places were really valleys, streams and lakes. Although it was possible to destroy these natural land and surface structures and equip them with human elements, this was no different from challenging nature. The 'settlements built in stream beds', which experts often warn about in floods and landslides, actually mean that there are concrete obstacles where the water should flow. Thus, the rainfall here turns into a stream again and nature returns to its essence. Prof. Dr. Mikdat Kadıoğlu concluded his speech by drawing attention to the disaster danger posed by the growth of cities and settlements built on stream beds.