Showing the value of green spaces from a climate perspective: a weather sensor network for city spaces in Tallinn

Grey infrastructures like buildings, roads and parking lots relate to surface sealing, lack of ventilation and anthropogenic heat – leading to effects like urban heat (UHI) and dry islands (= higher temperatures and lower relative humidity), and impact surface runoff during precipitation events. Hence, urban climate conditions differ significantly from their rural surroundings, demanding more granular data to quantify the effect city space has on weather parameters. However, observations and weather forecasts are usually made for rural areas, representative for a larger area – not for spaces where most people live, work and sleep. While a lot of data indeed exist for urban areas already – e.g., from satellites, radar stations and climate models – they all need calibration from measurements, in the city itself.

Tallinn is the European Green Capital 2023. While it strives making green spaces more accessible for its people, grey infrastructure development is continuing and even expanding, sustaining and increasing the city’s urban heat and dry islands. On the other hand, Tallinn is conserving and investing in green infrastructure, like turning an old railway track into a green corridor and publicly open space (the so-called “Pollinator Highway”). This corridor connects living quarters of Tallinn`s outskirts with central areas and supports social inclusion by passing through diverse socio-economic districts.

We created a concept to show the value of this green corridor for urban climate conditions. In May 2022, SEI Tallinn set up a network of 18 weather sensors measuring temperature, relative humidity and precipitation. The majority of stations are placed in green (5), urban green (5) and urban grey (5) spaces in the vicinity of the “Pollinator Highway”, with two more nearby the sea (to quantify land-sea-wind effects) and one near the official weather station. Data are open access, and live measurements publicly accessible.

In this contribution, we evaluate the results of 10 months of measurements, with a spatiotemporal focus on how and where Tallinn’s UHI enhances the impacts of heat and mitigates cold waves. With the data presented in this contribution, we make urban climate challenges visible and climate communication more relevant to people, show the climatic value of green compared to grey city spaces (especially during heat waves) to municipal decision-makers and Tallinn’s citizens, determine the effect of the sea on Tallinn's climate and how it shapes Tallinn`s UHI, and finally support climate resilience and tailored adaptation solutions.