A changing climate is expected to increase average summer temperatures and the frequency and intensity of hot days. Heat-waves (heat or hot weather that lasts for several days) are associated with significant morbidity and mortality. These have caused far more fatalities in Europe in recent decades than any other extreme weather event. According to a study by Robine et al. , the 2003 heat wave caused around 70,000 deaths across Europe!
Heat-related problems are greatest in cities. The urban population of the world has grown rapidly from 751 million in 1950 to 4.2 billion in 2018. According to a United Nations data set 55% of the world’s population lives in urban areas, a proportion that is expected to increase to 68% by 2050 .
Among many interrelated factors connected with heat-related problems, the Urban Heat Island (UHI) effect plays an important role. The UHI effect refers to the positive temperature difference between an urban area and its surroundings, and it is one of the most well-known consequences of urbanization on local climate . The heat that is absorbed during the day by the buildings, roads and other constructions is re-emitted after sunset, creating high temperature differences between urban and rural areas . The form and size of this phenomenon varies in time and space as a result of meteorological (e.g. temperature, precipitation, humidity, cloud cover), location and urban characteristics .
Traditionally, Urban Heat Island was defined as the air temperature difference between the urban zone and its surroundings, known as the canopy UHI, and was studied using in-situ weather stations . The advent of satellite data has allowed to define a new kind of Urban Heat Island - the surface UHI, which is the difference in land surface temperature (LST) between the urban zone and its surrounding non-urban area . Although Canopy and surface UHI intensities are similar at the annual scale, they may have different daily and seasonal variabilities .
The negative impacts of UHI according to N. Wong and Y. Chen :
- Air quality: UHI effect increases the possibility of the formation of smog that is highly sensitive to temperatures since photochemical reactions are more likely to occur and intensify at higher temperatures. Atmospheric pollution can be aggravated due to the accumulation of smog. In addition, the increased emissions of ozone precursors from vehicles is also associated with the high ambient temperature;
- Human mortality and disease: it is associated with significant morbidity and mortality; the UHI effect involves the hazard of heat stress related injuries which can threaten the health of urban dwellers;
- Waste of natural resources: higher temperatures in cities increase cooling energy consumption and water demand for irrigation. As a result, more electrical energy production is needed and this will trigger the release of more greenhouse gas due to the combustion of fossil fuel. It also includes the increased pollution level and energy costs.
Cities requires detailed and continuous monitoring to detect any areas of risk. Due to limited monitoring stations, the measured air UHI usually fail to provide sufﬁcient spatial details for urban land use planning and climate change research. Satellite images from multiple sensors allow to monitor land use change, surface permeability and temperature (Figure 1) to easier identify urban heat islands. The use of satellite data has reduced the inconsistency in measurement techniques by allowing a standardized data collection approach that can be implemented for multiple cities.
Figure 1. Land Surface Temperature in Warsaw (Poland) calculated from Landsat 8 images
EarthClimate pilot is proposed in the frame of the SnapEarth project and has the ambition to tackle the above-mentioned issues delivering value-added services to support climate monitoring activities. A variety of Earth Observation (EO) and in-situ data are on different platforms and available in different formats making them difficult to use and significantly extends the time of their acquisition. EarthClimate will simplify the use of climate-related EO data, it provides data, tools and services, tailored to the needs of the citizens, planners and decision-makers, enabling informed decision making.
The EarthCimate will focus on providing and enabling the analysis of data related to:
• Air quality and
• Urban Heat Islands monitoring
and additional functionality will be the use of data developed as part of EarthSignature, i.e. the classification of land cover/use.
The EarthClimate pilot will enable obtaining information from satellite images (e.g. Land Surface Temperature, surface albedo, methane, carbon monoxide, NO2 and SO2 values), meteorological data and other in-situ data.
 Robine, J.M., Cheung, S.L., Le Roy, S., Van Oyen, H., Griffiths, C., Michel, J.P., Herrmann, F.R., 2008, Death toll exceeded 70,000 in Europe during the summer of 2003. C. R. Biologies 331, 171–178.
 68% of the world population projected to live in urban areas by 2050, says UN, 2018; https://www.un.org/development/desa/en/news/population/2018-revision-of-world-urbanization-prospects.html
 Souch, C., Grimmond, S., 2006, Applied climatology: urban climate. Progr. Phys. Geogr. 30 (2), 270–279.
 Asimakopoulos D., Assimakopoulos V., Chrisomallidou N., Klitsikas N., Mangold D., Michel P., Santamouris M., Tsangrassoulis A., 2001, Energy and Climate in the Urban Built Environment, M. Santamouris (Ed.). London. James & James Publication.
 Oke T.R, 1987, Boundary Layer Climates (2an edn.). New York. Methuen and Co. Ltd.
 Voogt, J., 2007, How researchers measure urban heat islands. In: United States Environmental Protection Agency (EPA), State and Local Climate and Energy.
 Rao, P.K., 1972, Remote sensing of urban heat islands from an environmental satellite. Bull. Am. Meteorol. Soc. 53 (7), 647.
 Chakraborty, T., Sarangi, C., Tripathi, S.N., 2016, Understanding diurnality and interseasonality of a sub-tropical urban heat island. Boundary-Layer Meteorol. 1–23.
 Wong N. H., Chen Y., 2009, Tropical Urban Heat Islands: Climate, Buildings and Greenery. London and New York. Taylor & Francis Press