Just a few days ago, temperatures in many parts of Poland reached 28 and, locally, even 30 degrees Celsius. Now, in some parts of the country, thermometers are showing less than 20 degrees, while the change in temperature is accompanied by heavy rainfall and sudden weather events. For residents, this primarily means major fluctuations in thermal comfort, but for cities it is a much more serious problem. The same urban space has to cope with both excess water and high temperatures within a short period of time, while infrastructure designed over many years for more predictable weather conditions is increasingly being exposed to completely different loads.
The issue is not limited to record temperatures, which attract public attention during the summer. For urban infrastructure, rapid transitions between different weather conditions are equally important. Heavy rain can deliver more water within several dozen minutes than a local drainage system is capable of handling, while several days later the same surface can once again become intensely heated. The problem is that infrastructure needed to deal with one of these phenomena may not solve the other at the same time. This is why solutions that allow cities to retain water, limit the heating of urban spaces and improve living conditions for residents at the same time are becoming increasingly important.
One of the most visible problems is the way cities manage rainwater. In densely built districts, a large share of the surface is covered with asphalt, concrete or other impermeable materials. When heavy rain occurs, water cannot infiltrate the ground where it falls. Instead, it quickly flows into drains and stormwater systems, and then enters infrastructure that can become overloaded when rainfall is particularly intense.
The consequences can include local flooding of streets, car parks, underground passages or lower lying parts of cities. The problem is particularly severe where buildings are densely concentrated and opportunities to create new green areas or permeable surfaces are limited. Every additional square metre of impermeable surface increases the amount of water that has to be handled by the drainage system during heavy rainfall.
At the same time, quickly removing water solves one problem but creates another. If rainwater almost immediately leaves the urban space, it does not replenish soil, trees or other vegetation. Several days later, when temperatures rise again, urban greenery therefore has less water available. As a result, the same area that has to deal with excess water during heavy rainfall may later struggle with a shortage of water.
This is why water retention is becoming one of the basic elements of urban adaptation to climate change. Instead of treating rainwater solely as a problem that needs to be removed as quickly as possible, part of it can be retained where it falls. Rain gardens, retention basins, reservoirs, permeable surfaces and appropriately designed green areas can slow down runoff and gradually transfer water into the ground.
The same street can become a problem several days later
For a city, what happens during heavy rainfall is not the only issue. Once the rain stops, surfaces made of concrete and asphalt begin to release the heat they have accumulated. In densely built districts with few trees and green areas, temperatures can remain higher than in areas with less intensive development.
Trees in such locations are much more important than simply providing aesthetic value. Their canopies provide shade, reducing the direct heating of pavements, squares and building facades. Vegetation also participates in the process of water evaporation, which affects local thermal conditions. However, if most of the water from earlier rainfall has been quickly discharged into the drainage system, urban greenery has limited opportunities to use it.
This is why water related solutions and measures designed to reduce urban overheating should not be planned separately. A retention reservoir can reduce pressure on the drainage system during heavy rainfall, while a properly designed green system can create a place where retained water is used by plants. Similarly, a permeable surface can reduce the amount of water flowing into the drainage system while also allowing the soil to be replenished.
– September shows that as summer comes to an end, weather challenges for cities do not end at all. Periods of high temperatures, cooling, heavy rainfall and strong winds can follow one another within a short period of time. Autumn is a good moment to remind ourselves that urban resilience needs to be built with different hazards occurring throughout the year in mind. That is why adaptation measures should not focus exclusively on the summer season. Multifunctional solutions are particularly important because they help both reduce the overheating of urban spaces and retain rainwater while lowering the risk of local flooding – says Dr. Eng. Amadeusz Walczak, Senior Environmental Consultant at Multiconsult Polska, specializing in the development of climate adaptation plans for cities.
Cities need infrastructure that can operate in several modes
Changing weather conditions mean that urban infrastructure can no longer be designed simply to withstand one type of hazard. Stormwater systems need to be capable of handling water during intense rainfall, but at the same time cities should reduce the amount of water that reaches the drainage system in the first place. The most effective solutions therefore combine technical infrastructure with green infrastructure and water retention.
In practice, this means changing the way urban spaces are designed. Instead of creating a completely impermeable square, permeable surfaces can be used to allow some water to enter the ground. Rather than directing all rainwater straight into the drainage system, a retention basin or rain garden can be used. A space that previously consisted only of a lawn without the ability to store larger amounts of water can be transformed into an area capable of temporarily retaining water during heavy rainfall and later releasing it into the ground.
Such solutions are also important because not every heavy rainfall event creates a problem throughout an entire city. The risk may be concentrated in specific locations where terrain, development patterns and insufficient drainage capacity cause water to accumulate quickly. A local authority therefore needs detailed knowledge of where the greatest problems occur and which solution will be effective in each particular location.
The same applies to high temperatures. Not every district heats up to the same extent. The greatest risk can be expected in areas with a high concentration of concrete and asphalt, few trees and large numbers of residents using public spaces. In such locations, increasing shaded areas, expanding greenery and reducing impermeable surfaces can produce a much greater effect than scattered measures implemented without taking local conditions into account.
Adaptation starts with data, not a single investment
There is no single set of solutions that can be applied to every Polish city. An area where the primary problem is periodic water scarcity requires a different approach from a district that is regularly flooded during intense rainfall, while a densely built city centre where overheating is the main concern requires yet another strategy.
That is why urban adaptation plans should identify specific risks and the locations where they occur. A local authority should know where water accumulates most rapidly during heavy rainfall, which sections of the drainage system are under the greatest pressure, where green areas are lacking, which streets and squares have the highest proportion of impermeable surfaces and where residents are most exposed to the effects of high temperatures.
Only on this basis can investment priorities be established. In one location, the priority will be upgrading drainage infrastructure, in another, building a retention reservoir, while elsewhere it may be increasing the number of trees and creating surfaces capable of retaining water. In many cases, the most economically rational approach will be to combine several functions within a single project, because the same investment can simultaneously reduce flood risk and improve thermal conditions.
The way new investments are planned also matters. If a new housing development, road or square is designed from the outset as a completely impermeable space, introducing retention measures later can be much more difficult and expensive. Adaptation should therefore not only mean fixing existing problems. It should also prevent the creation of new areas vulnerable to the effects of extreme weather events.
Weather changes also affect residents and energy demand
Weather fluctuations have an infrastructure dimension, but their effects are felt directly by residents. During periods of high temperatures, the strain on the human body increases, particularly for older people, children and those with chronic illnesses. Densely built areas without shade can further worsen outdoor conditions, while overheated homes and buildings increase the demand for cooling.
This in turn affects energy consumption. During heatwaves, air conditioning and other systems used to lower indoor temperatures operate more intensively, increasing electricity demand. If high temperatures persist for several days, the additional load can affect a large part of the urban building stock at the same time.
Greenery can help reduce part of this problem, particularly where trees shade buildings and public spaces. It cannot, of course, replace indoor cooling systems, but it can reduce the extent to which the surrounding environment heats up. From a city planning perspective, it is therefore important to design spaces in a way that addresses the source of the problem rather than simply responding to its consequences.
The biggest challenge is the speed of change
The change in weather conditions in September clearly shows why preparing a city for only one type of extreme weather event may not be enough. Heat requires measures that reduce overheating and protect residents, intense rainfall requires effective water management, while strong winds can create additional risks for trees, infrastructure and transport. All of these phenomena can occur within short intervals.
Urban resilience therefore needs to be built as a system in which individual solutions complement one another. Retention reduces the amount of water immediately directed into drainage systems, greenery improves thermal conditions and can use retained water, while appropriately designed surfaces reduce both runoff and the heating of urban areas. In many cases, cities therefore do not have to choose between protection against heavy rainfall and protection against heat. A much better result can come from designing urban spaces to perform several functions at the same time.
For local authorities, this means moving away from treating extreme weather as an isolated event that is addressed only when it occurs. The key is to identify in advance the locations most vulnerable to overheating and flooding, determine how these risks can be reduced and consistently take them into account when carrying out renovations, developing new investments and planning urban space. Weather will continue to shift from heat to heavy rainfall and from high temperatures to cooling, while cities need to be prepared for all of these scenarios rather than only the one that happens to be attracting the most attention at a given moment.
Multiconsult Polska develops projects related to urban resilience
Multiconsult Polska is a multidisciplinary company providing design, supervision and advisory services in technical projects and environmental protection. The company operates in areas including transport and infrastructure, construction and industry, including the oil and gas sector.
In the context of adapting cities to climate change, combining expertise in infrastructure design with knowledge of environmental protection is particularly important. This makes it possible to analyse not only individual solutions but also how investments affect the functioning of the entire urban space. The objective is to design infrastructure taking into account both safety and environmental conditions, as well as future changes in the way cities operate.
The September weather swing is therefore more than a short term change in temperature. It shows that urban infrastructure has to be prepared for a situation in which a period of high temperatures is followed by heavy rainfall and temperatures then rise again. The most valuable investments will be those capable of responding to several of these problems simultaneously by retaining water, reducing overheating and improving living conditions for residents.
