Introduction

For the second time in as many months, Europe was gripped by an extreme heat wave, breaking temperature records in 12 countries. Record high temperatures were set on Thursday, July 25, 2019, in the Netherlands at 40.4 °C (104.7 °F), and Belgium at 41.8 °C (107.2 °F). Germany reached 42.6 °C (108.7 °F), as did Paris, France, which broke a record that had stood for over 70 years by more than 2 degrees Celsius. 

For Europeans, this may sound like a “broken record” as the continent suffered a separate extreme heat wave just a month prior in late June, when eight countries experienced record-breaking heat, including France’s all-time highest recorded temperature at 45.9 °C (114.6 °F). While these temperatures are still far from the highest recorded temperatures on Earth, they are abnormal for Europe, where less than 5% of households are air-conditioned. Exposure to extreme heat waves can lead to significant health risks, such as heat stroke and cardiovascular and respiratory failure, which can result in death. The elderly population is particularly at risk during these extreme heat events.

Extreme heat events are even more dangerous in large cities, as areas of dense impervious surfaces from buildings, roads, and parking lots absorb heat during the day and reradiate the heat back into the city at night. This leads to overall warmer temperatures in cities than the surrounding areas, known as the Urban Heat Island (UHI) effect. Fortunately, there are solutions that can be put in place to mitigate the impacts of UHIs and extreme heat waves in cities. Those include long-term solutions, such as increasing green space and whitening roofs. 

There are also potential short-term solutions, such as installing mist spray systems in public places. One way to identify at-risk “hot spots” within cities that would benefit from these solutions during heat waves is through remote sensing. One major benefit in using remote sensing data, in addition to in-situ weather station temperature readings, is that they provide a spatially continuous map of urban temperatures. Remote sensing sensors detect land surface temperature (LST), or the temperature of the surface being detected, similar to air temperature measured at weather stations, but the two measurements can differ, especially during the day as LST skyrockets over sunlit areas. 

NASA’s ECOsystem Spaceborne Thermal Radiometer (ECOSTRESS) is a new sensor that captures LST at 70-meter (m) resolution. Installed on the International Space Station (ISS), ECOSTRESS is novel in that it captures multispectral thermal observations globally from space at relatively high resolutions at different times throughout the day.

Science Objectives

ECOSTRESS captures radiance, which is converted to emissivity and LST. In turn, ECOSTRESS produces higher level products such as Evapotranspiration, Evaporative Stress Index, and Water Use Efficiency. Check out all available ECOSTRESS products available from NASA’s Land Processes Distributed Active Archive Center (LP DAAC). 

While the main goal of the ECOSTRESS mission is to better understand how much water plants need and how they respond to stress, ECOSTRESS can also be used to observe heat-related phenomena, such as extreme heat waves and the UHI effect. The images to the right and below are ECOSTRESS LST observations from July 24, 2019—in the middle of the record-breaking heat wave. In the image above, notice the warmer cities evident in shades of orange-red from the cooler surrounding agricultural landscape. All-time maximum temperatures for the countries of Belgium and the Netherlands were broken on this day—in Eindhoven, Netherlands at 39.3 °C (102.7 °F) and Angleur, Liege, Belgium at 40.2 °C (104.4 °F). However, both records only stood for one day as temperatures climbed even higher in both countries on July 25, 2019.

Major Findings

The image below shows an ECOSTRESS observation over Paris, France, from the evening of July 24, 2019. Dense regions of the city or areas with higher impervious surface area appear warmer than surrounding rural forests and agricultural areas, in part because of the UHI effect and the thermal characteristics of different land surfaces. Notice the contrasting temperatures between Charles De Gaulle (CDG) International Airport and cooler surfaces such as the Seine River, or the gardens at the Palace of Versailles. 

Using another sensor archived at LP DAAC, the Terra Advanced Spaceborne Thermal Emission and Reflection Radiometer’s (ASTER) Level 1 Precision Terrain Corrected Registered At-Sensor Radiance (AST_L1T.003) product allows for a higher resolution (15-m) natural color view. That can be useful when combined with the relatively high resolution from ECOSTRESS LST in order to identity localized regions within an urban area that may be at higher or lower risk of heat-related illness during an extreme heat wave event.

References

Publication References

Gerretsen, I., Yeung, J., 2019, Europe’s heat wave is shattering temperature records and cities are struggling to cope, accessed August 12, 2019.

Henley, J., 2019, All-time temperature records tumble again as heatwave sears Europe, accessed August 12, 2019.

Hook, S., Hulley, G., 2019, ECOSTRESS Land Surface Temperature and Emissivity Daily L2 Global 70 m V001 [SDS_LST]: NASA EOSDIS Land Processes DAAC, accessed August 12, 2019. doi:10.5067/ECOSTRESS/ECO2LSTE.001

Hulley, G.C., Shivers, S., Wetherley, E., 2019, New ECOSTRESS and MODIS land surface temperature data reveal fine-scale heat vulnerability in cities: a case study for Los Angeles county, California: Remote Sensing, In press.

NASA JPL, 2019, ECOSTRESS, accessed August 12, 2019.

NASA LP DAAC, 2015, ASTER Level 1 Precision Terrain Corrected Registered At-Sensor Radiance V003 [Bands 1-2-3N]: NASA EOSDIS Land Processes DAAC, accessed August 12, 2019. doi:10.5067/ASTER/AST_L1T.003

Smith, E., 2019, NASA's ECOSTRESS Maps European Heat Wave From Space, accessed August 23, 2019.

Wikipedia contributors, 2019, July 2019 European heat wave, In Wikipedia, The Free Encyclopedia, accessed August 13, 2019.

Image References

ECOSTRESS Granule ID

ECOSTRESS_L2_LSTE_05952_004_20190724T192328_0600_01

Data Citation

Hook, S., G. Hulley. ECOSTRESS Land Surface Temperature and Emissivity Daily L2 Global 70 m V001. 2019, distributed by NASA EOSDIS Land Processes DAAC, https://doi.org/10.5067/ECOSTRESS/ECO2LSTE.001. Accessed 2019-08-14.

ASTER Granule ID

AST_L1T_00308032018105334_20180810131027_26944, AST_L1T_00308032018105343_20180810131258_3338, AST_L1T_00308032018105352_20180810130926_23198

Data Citation

NASA LP DAAC. ASTER Level 1 Precision Terrain Corrected Registered At-Sensor Radiance V003. 2015, distributed by NASA EOSDIS Land Processes DAAC, https://doi.org/10.5067/ASTER/AST_L1T.003. Accessed 2019-08-14.