Urban Climate Measurements in Hannover (Germany)

In the city of Hannover, capital of the federal state Lower Saxony, the urban climate was investigated with different methods:

- Stationary measurements at five locations

- Mobile measurements by cars in three campaigns during summer conditions

- Mobile measurements by trams

- Simulation of the temperature distribution in the urban area with an urban climate model

Project duration: June 2017 to December 2020

Project partners: German Weather Service, City of Hannover, State of Lower Saxony, ÜSTRA Hannoversche Verkehrsbetriebe AG

Stationary measurements (temperature, relative humidity, wind) at three stations in the dense urban area, additionally at two stations in the surrounding area. The temperature measurements show on average up to 1.0 K higher temperatures at the urban stations. The differences are greater at night than during the day, and greater in spring and summer than in autumn and winter. The inner city shows significantly more days with heat (summer days, heat days, tropical nights) and fewer frost days than in the surrounding area.

Profile measurement runs were carried out with a passenger car on two fixed routes through Hannover. Each measurement campaign lasted two to three days, during which measurement runs were carried out at three fixed times. Measurements of air temperature and relative humidity took place continuously during the trip. The comparison of the averaged temperatures of the measurement runs with the surrounding area shows hardly any differences during the afternoon measurements. During the early morning runs, however, there were large differences of up to 4.3 K and up to 3.2 K during evening runs.

Tram measurements were made throughout the entire route network during regular service. Three trams were equipped with measuring devices (for temperature and relative humidity), in one streetcar interior measurements were also made. The temperature distribution was evaluated for various route sections. Especially the inner city, commercial areas, residential areas and urban green areas were considered. The tram measurements are presented in detail in another paper.

Simulation of the temperature distribution in the urban area of Hannover with the urban climate model MUKLIMO_3: The simulations show the different extension of the urban heat island during the day. In the afternoon, striking temperature differences are shown within a small area. Hot inner-city areas are directly adjacent to cool areas characterized by water bodies, meadows and parks. In the late evening, overheated urban areas occupy significantly more space, and the cool  areas have decreased. The urban heat island is most extensive in the early morning hours. Almost the entire urban area is overheated, only at the city boundary are still cool regions.