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What is urban climate?

City climate is defined as "local climate which differs from that in neighbouring rural areas, as a result of urban development". This means air temperature, precipitation, concentration of air pollutants, and wind speed often differ from the surrounding areas. Differences in air temperature between a city and its surrounding areas can reach up to 10°C at night. City effects on precipitation intensity and wind fields are also documented.

Why do cities heat up butdo not cool off as much?

Cities are characterized by densely built-up areas and surface sealing. This leads to higher air temperatures and reduced wind speeds. Buildings and streets store the energy of solar radiation during the day and release this energy in form of heat at night. Wind speed, and thus ventilation of the city, is often reduced by buildings. Vegetation such as urban trees or green spaces that could provide shade and cooling by evaporation can be rare or missing altogether.

What are the consequences?

Heat waves particularly affect the elderly and the sick, since cardiovascular diseases increase the risk of death during the heat. Increasing temperatures also increase the number of heavy precipitation events in cities, thereby causing floods whose impact is much more severe in cities than in the open countryside: the sealed surfaces of the city increase water runoff and prevent seeping of rainwater into the ground. The sewer system provides only limited buffer for rainwater and can overflow if precipitation is high. The increased likelihood of heavy precipitation and hail events can require additional insurance services due to the enormous damage they can cause in a city.

Why is it important to monitor urban climate?

The world's population living in urban areas is more than half today, and constantly rising. The increasing number of people in cities also require more living space and extended infrastructure. With increasing infrastructure density, further temperature increases are likely or need compensation measures even in cities where this is not yet necessary. Extensive monitoring of the urban climate is the basis for significantly improving the quality of life by evaluating suitable urban measures. Municipal companies can improve their efficiency (traffic, road and construction management, water budgets, etc.) if they have access to close-meshed (temperature, precipitation, etc.) measurements in the city. Organizers, planners, and Insurance companies can benefit from better risk assessment for heat, precipitation, wind and other factors.

How to better predict the urban climate and its effects?

The first step to better understand a city’s climate and its possible future change is to install a modern sensor network at suitable locations within the city to measure and store hourly data for air temperature, precipitation, and other variables. Based on these data, special city climate models fill the gaps between the measurements and generate a comprehensive climate information system for the city. This system can then produce risk maps and assessments, as well as forecasts, warnings, and planning scenarios. The system can be used to inform the citizens, support decision makers, and help develop plans to improve the city climate.

What is a Local Climate Zone (LCZ)?

LCZ are a means to classify surface types that affect the local climate differently. 10 LCZ types (“1-10”) describe built-up areas in terms of building types and spatial arrangements, materials, human activities, plants, ground surface properties, etc. 7 more types (“A-G”) describe land cover in terms of plant cover and ground surface properties. The definitions of LCZ were introduced in Stewart, I.D. and Oke, T.R. 2012. Local Climate Zones for urban temperature studies. Bulletin of the American Meteorological Society, 93: 1879-1900.

1. Compact high-rise:
LCZ 1 is characterized by a dense mix of tall buildings (more than 10 floors) with concrete, steel, stone and glass construction materials. There is little or no vegetation and the surface is mostly paved.

2. Compact midrise:
LCZ 2 is characterized by a dense mix of midrise buildings (3-9 floors) with concrete, steel, stone and glass construction materials. There is little or no vegetation and the surface is mostly paved.

3. Compact low-rise:
LCZ 3 is characterized by a dense mix of low-rise buildings (1-3 floors) with concrete, steel, stone and glass construction materials. There is little or no vegetation and the surface is mostly paved.

4. Open high-rise:
LCZ 4 is characterized by an open arrangement of tall buildings (more than 10 floors) with concrete, steel, stone and glass construction materials. Low plants and scattered trees create a permeable landcover.

5. Open midrise:
LCZ 5 is characterized by an open arrangement of midrise buildings (3-9 floors) with concrete, steel, stone and glass construction materials. Low plants and scattered trees create a permeable landcover.

6. Open low-rise:
LCZ 6 is characterized by an open arrangement of low-rise buildings (1-3 floors) with concrete, steel, stone and glass construction materials. Low plants and scattered trees create a permeable landcover.

7. Lightweight low-rise:
LCZ 7 is characterized by a dense mix of single-story buildings with lightweight construction materials like wood, thatch and corrugated metal. There is little or no vegetation and the surface is mostly hard-packed.

8. Large low-rise:
LCZ 8 is characterized by an open arrangement of large low-rise buildings (1-3 floors) with concrete, steel, stone and metal construction materials. There is little or no vegetation and the surface is mostly paved.

9. Sparsely built:
LCZ 9 is characterized by a sparse arrangement of small or medium-sized buildings in a natural setting. Low plants and scattered trees create a permeable landcover.

10. Heavy industry:
LCZ 10 is characterized by low-rise and midrise industrial structures like towers, tanks and stacks with metal, steel and concrete construction materials. There is little or no vegetation and the surface is mostly paved or hard-packed.

A. Dense trees:
LCZ A is characterized by deciduous and/or evergreen tree. It is a heavily wooded landscape and the landcover is mostly permeable. The zone functions as natural forest, tree cultivation or urban park.

B. Scattered trees:
LCZ B is characterized by deciduous and/or evergreen tree. It is a lightly wooded landscape and the landcover is mostly permeable. The zone functions as natural forest, tree cultivation or urban park.

C. Bush, scrub:
LCZ C is characterized by an open arrangement of bushes, shrubs and short, woody trees. the landcover is mostly permeable with bare soil or sand. The zone functions as natural scrubland or agriculture.

D. Low plants:
LCZ D is characterized by a featureless landscape of grass or herbaceous plants or crops. There is little or no trees. The zone functions as natural grassland, agriculture, or urban park.

E. Bare rock or paved:
LCZ E is characterized by a featureless landscape of rock or paved cover. There is little or no vegetation. The zone functions as natural desert (rock) or urban transportation.

F. Bare soil or sand:
LCZ F is characterized by a featureless landscape of soil or sand cover. There is often little or no vegetation. The zone functions as natural desert or agriculture.

G. Water
LCZ G is characterized by large, open water bodies such as seas and lakes, or small bodies such as rivers, reservoirs, and lagoons.