Heavy rains that hit Istanbul on October 14 caused floods in homes and workplaces, disruptions in transportation, and loss of life.
According to the first data announced by the Istanbul Governorship as of 20:00 on October 14, 1,277 floods, 15 landslides and 47 stranding events were recorded. In Beykoz-Ömerli, 193.84 kilograms of precipitation per square meter fell.
So why does Istanbul get flooded during heavy rains?
Scientific studies show that the answer lies not only in the amount of rainfall but also in how the city manages water.
HOW DOES CONCRETEMENT INCREASE THE RISK?
Seda Ertan and Rahmi Nurhan Çelik's research, published in Sustainability magazine in 2021, examined an area of 1,653 hectares in the Kağıthane Creek basin.
The researchers compared different construction and stormwater management scenarios with computer models.
The results showed that practices such as green roofs and permeable road surfaces can reduce runoff and flood hazards.
This is because soil and vegetation retain some of the precipitation, while asphalt and concrete cause water to quickly run off the surface. Thus, the amount of water reaching the drainage systems in a short time increases.
BUILDING IN STREAM BEDS
One of the heaviest floods in Istanbul occurred around Ayamama Creek on September 9, 2009. 32 people died in the disaster.
The research of Sezar Gülbaz and his colleagues, published in the Journal of Hydrologic Engineering, examined the flood using computer models.
According to the model results, the water depth reached approximately 11 meters at some critical points of the basin. This value does not mean that the same depth is measured in the entire basin.
Stream beds do not only consist of channels through which water flows under normal conditions. During heavy rains, the surrounding flood plains can also become water spreading areas.
WHY IS THE EFFECT DIFFERENT EVERYWHERE?
An Istanbul study published in the journal Sustainable Cities and Society in 2022 evaluated flood danger and social vulnerability together.
The study showed that rainfall, as well as impermeable surfaces and the drainage network, are important in risk assessment.
The main risk factors are as follows:
Concreting: It reduces the infiltration of rainwater into the soil.
Drainage capacity: Water accumulates when the capacity of the drain system is exceeded.
Stream beds: Construction in areas where flood water can spread can increase the damage.
Location of buildings: Basement floors and buildings in low-lying areas may be more susceptible to floods.
WHAT IS THE IMPACT OF CLIMATE CHANGE?
The Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) reveals that global warming is contributing to the exacerbation of extreme precipitation in many regions.
Every 1 degree increase in temperature increases the atmosphere's capacity to hold water vapor by approximately 7 percent. However, this does not mean that the amount of precipitation will increase at the same rate in every region.
Case-specific scientific analysis is required to determine the extent to which the recent disaster in Istanbul is linked to climate change.
WHAT IS THE SOLUTION PROPOSED BY SCIENCE?
Research indicates that larger drainage channels alone may not be enough to reduce flood risk.
Protecting stream floodplains, increasing permeable surfaces, green infrastructure applications and planning drainage systems according to extreme rainfall scenarios should be addressed together.
The main conclusion of scientific studies is this:
The flood risk is determined not only by the intensity of the rainfall, but also by how safely the city manages water.
CAN FLOODS BE PREVENTED IN ISTANBUL?
According to scientific research, although it is not possible to prevent excessive rainfall, it is possible to reduce the risk of them turning into floods and the damage they cause.
For this, simply expanding rainwater channels is not enough. Stream beds and natural floodplains need to be protected, concreting should be limited and green areas that can retain rainwater should be increased.
Solutions suggested in the research include green roofs that retain some of the rainwater by being covered with vegetation, road pavements that allow water to pass into the ground, and systems that temporarily store rainwater.
However, the effect of these measures varies depending on the geographical characteristics of the region and the intensity of the rainfall.
The common message of the specialist studies is clear:
