Handheld access to actionable heat risk and response information in eight global cities

Organization: World Meteorological Organization (WMO)

Year: 2023

Published in:

WMO (2023). 2023 State of Climate Services: Health - No. 1335


The health impacts of extreme heat are predictable and largely avoidable, provided that city authorities have access to timely and location-specific information. With the right data and tools, city authorities can identify local hot spots, optimize the allocation and management of cooling centres, ensure sufficient drinking water spots and cooling spaces and communicate the health-related risks of excessive heat. Citizens and visitors can plan their daily lives in the city safely knowing the risks, and can adapt their routines accordingly. The challenge then is to improve access to information so that city authorities can reduce heat-related illness and deaths.



EXTREMA Global148 is a portfolio of digital services based on open Earth observation data as well as climate and atmosphere models and local data, targeting cities and citizens with city-specific customizations. It was originally designed to lessen the impacts of heatwaves on public health, and to make cities more heat resilient. The core services of EXTREMA Global include a free, multilingual mobile app that uses data and services to provide the current heat risk at the location of the user and recommendations for health protection, including directions to the nearest cooling places and drinking water spots and public announcements from city authorities. The app supports multiple profiles, allowing users to check on family members in multiple locations. The city authorities access tools and alerts through a dashboard to help them manage their resources to reduce heat exposure. City authorities also have access to satellite-derived maps showing the distribution of surface temperature in order to identify hot spots and areas that need intervention, through for example, the planning, design and management of urban infrastructure. The smartphone app also has optional modules that allow for the integration of air quality data from Copernicus Atmospheric Monitoring Service (CAMS) and provision of relevant health instructions. EXTREMA Global services are already being used in the municipalities of Athens, Milan, Paris, Rotterdam, Greater London (UK), and in Chicago, Tampa and Newark in the USA.



Athens (Greece) was the first city in which the concept was adopted in 2016. City authorities worked to design the app to meet the city requirements, and have since included the app in the #CoolAthens campaign. They have also included the add-on to provide air quality data at the location of the user, and use high-resolution temperature distribution maps to guide planning. The combination of air quality and heat risk proved to be very useful in July 2021 when Athens experienced a severe heatwave that lasted 10 days and saw temperatures reach about 44 °C, with very poor air quality due to nearby wildfires sparked by the heat. The EXTREMA app suggests “cool routes” where users can walk safely around the city, for example, between tourist attractions, a feature much needed for tourists. In July 2023, during a heatwave that lasted 14 days, app requests by Athenians and visitors reached 10 000 hits. Furthermore, the app contributed drastically to strengthening communication between the departments of the municipality to exchange know-how and data. In Milan, hundreds of drinking water spots are mapped in the app, making use of the digital infrastructure to also decrease the use of plastic bottles. Publicity and dissemination by the city authorities play a critical role in the use and impact of the app, with peak usage dates coinciding with days in which the city promoted the app in the local press. In 2022, the app received 6 324 requests for service from Milan. Milan is now using digital services to calculate the safest and coolest routes for bicycles.


In Athens, the EXTREMA app supports six languages to help tourists find their nearest cooling space and the coolest route to their destination.


PARTNERS National Observatory of Athens, Group on Earth Observations (GEO), Global Urban Observation and Information (GUOI) initiative, ARTi Analytics B.V., Copernicus Atmospheric Monitoring Service (CAMS), Bloomberg Associates