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Extreme Heat Data Pathfinder

Information on extreme heat events including what it is, who is most vulnerable, and how to avoid heat-related deaths.

Information on extreme heat events. Credit: Center for Disease Control (CDC)

According to the United States Global Change Research Program, heat waves are occurring more frequently in major cities across the nation. Heat waves are periods of abnormally hot and/or humid weather, lasting a few days to weeks at a time. In the 1960s, major cities in the U.S. experienced, on average, about two heat waves per year. In the 2010s that number rose to more than six heat waves. Not only are cities experiencing more extreme heat events, the seasons are also lasting longer, on average 47 days longer than in 1960. Even under different climate models and emission scenarios, results indicate that extreme heat events worsen.

Humidity is an important factor in heat index assessment. When the humidity is high, water does not evaporate as easily and so it becomes difficult for the body to cool off through sweating. The heat index incorporates both temperature and humidity and is used to determine public health warnings for areas experiencing heat waves. The public health impacts of heat waves include exhaustion or heat stroke, and even death. According to the Center for Disease Control, extreme heat results in about 600 deaths per year in the U.S, with the elderly, very young, outdoor workers, and people with mental illness and chronic diseases at higher risk.

In monitoring heat waves, it's important to access long-term data records to assess abnormalities from the norm. Using remote sensing data can be an asset in determining climate trends, as several satellite platforms have been acquiring data over many years. For example, the Terra satellite has been acquiring land surface temperature data since 2000. With consistent and continuous data coverage, reliable temperature and humidity anomalies can be assessed.

Find Temperature Data

Find Temperature Data

​Surface air temperature, measured in Kelvin,​ from the Atmospheric Infrared Sounder (AIRS), May 9, 2020, visualized in Panoply.

Surface air temperature, measured in Kelvin, from the Atmospheric Infrared Sounder (AIRS), May 9, 2020, visualized in Panoply.

Temperature is useful for assessing changes in weather and climate patterns that are critical for monitoring and responding to extreme heat events. By calculating the average temperature over a range of time, typically about 30 years, and comparing the forecasted high temperature over the forthcoming days to that average, one can determine if temperatures are indeed abnormal for that time period. An anomaly analysis or difference map is necessary to do this and can be created in Giovanni and Panoply (see the Tools for Data Access and Visualization section). Giovanni provides monthly and seasonal average maps, as well as the time-averaged map for the month or given time period of investigation. The netCDF can then be downloaded and opened in Panoply, where you can create a difference map with the "combine plot" option (see the Earthdata webinar Create Difference Maps for NASA Data w/Panoply, Giovanni & Excel for more information on this process).

Air Surface Temperature

Research-quality data products can be accessed via Earthdata Search:

  • AIRS Surface Air Temperature from Earthdata Search
    The Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite gathers infrared energy emitted from Earth's surface and atmosphere globally every day. AIRS data are daily, 8-day, and monthly at 1 degree and the Level 3 data products are provided in either the descending (equatorial crossing North to South at 1:30 a.m. local time) or ascending (equatorial crossing South to North at 1:30 p.m. local time) orbit. When you open the Hierarchical Data Format (HDF) file (in a program like Panoply or QGIS), you will see an ascending option and a descending option each with SurfAirTemp.
  • MERRA-2 Temperature from Earthdata Search
    The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) provides data beginning in 1980. Due to the amount of historical data available, MERRA-2 data can be used to look for trends and patterns, as well as anomalies. There are several options available: 1-hourly, 3-hourly, 6-hourly. These options provide information on surface skin temperature, the air temperature at 2 m, and the air temperature at 10 m.

Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, or a time series through an online interactive tool, Giovanni. Follow these steps to plot data in Giovanni: 1) Select a map plot type. 2) Select a date range. Data are in multiple temporal resolutions, so be sure to note the start and end date to ensure you access the desired dataset. 3) Check the box of the variable in the left column that you would like to include and then plot the data. For more information on choosing a type of plot, see the Giovanni User Manual.

Data, often in near real-time (NRT), are available for visualization in Worldview:

Land Surface Temperature

Satellite images show the relationship between the characteristics of a landscape, and day and night surface skin temperature. Heavily forested areas remain relatively cool throughout the day, while barren and arid areas can be tens of degrees warmer. These images were acquired in the early morning and afternoon of July 6, 2011.

Satellite images show the relationship between the characteristics of a landscape and day and night surface skin temperature. Heavily forested areas remain relatively cool throughout the day, while barren and arid areas can be tens of degrees warmer. These images were acquired in the early morning and afternoon of July 6, 2011. Credit: NASA Earth Observatory

Land surface temperature research-quality data products from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument (on both the Aqua and Terra satellites) the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument on the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) satellite, the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard Terra, and the ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS) can be accessed directly from Earthdata Search. In addition, the North American Land Data Assimilation System (NLDAS) monthly climatology dataset, accessible from Earthdata Search, contains a series of land surface parameters simulated from the Noah land-surface model, from 1980-2009.

To quickly extract a subset of ECOSTRESS, MODIS, or VIIRS data for your region of interest, use the LP DAAC AppEEARS tool or the ORNL DAAC subsetting tools.

Landsat data from USGS’ Earth Explorer are available via Earthdata Search. Note that you will need a USGS login to download the data.

Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, or a time series through an online interactive tool, Giovanni. Follow these steps to plot data in Giovanni: 1) Select a map plot type. 2) Select a date range. Data are in multiple temporal resolutions, so be sure to note the start and end date to ensure you access the desired dataset. 3) Check the box of the variable in the left column that you would like to include and then plot the data. For more information on choosing a type of plot, see the Giovanni User Manual.

  • NLDAS Surface Temperature in Giovanni
    There are a variety of different options including hourly and monthly data. North American Land Data Assimilation System (NLDAS) data are land model output files from 1979 to present. There is also a monthly climatology dataset, which contains a series of land surface parameters simulated from the Noah land-surface model, from 1980-2009.

Data can be visualized in Worldview:

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Find Humidity Data

Find Humidity Data

Relative humidity at 2 m above the surface from MERRA-2 visualized in the Prediction of Worldwide Energy Resources Data Access Viewer. The graphs display percent relative humidity for the single point over South Carolina.

Relative humidity at 2 m above the surface from MERRA-2 visualized in the Prediction of Worldwide Energy Resources Data Access Viewer. The graphs display percent relative humidity for the single point over South Carolina.

Humidity must be factored in when determining the heat index for an area. For example, if the air temperature is 96°F and the relative humidity is 65%, the heat index, or how hot it feels, is 121°F. In this example, without factoring in humidity, a heat advisory would never be issued, although it feels way above normal temperatures. Heat advisory, watches, and warnings vary across the country, especially for areas that are not used to dangerous heat conditions. Refer to the National Weather Service for a general rule of thumb.

Research-quality data products can be accessed via Earthdata Search:

  • AIRS Relative Humidity from Earthdata Search
    AIRS data are daily at 1 degree and the Level 3 data products are provided in either the descending (equatorial crossing North to South at 1:30 a.m. local time) or ascending (equatorial crossing South to North at 1:30 p.m. local time) orbit. Note that the data were acquired only until 2016.
  • MERRA-2 Humidity from Earthdata Search
    There are several options available: 1-hourly, 3-hourly, 6-hourly. These options provide information on surface specific humidity, specific humidity at 2 m, and relative humidity.

Data products can be visualized as a time-averaged map, an animation, seasonal maps, scatter plots, or a time series through an online interactive tool, Giovanni. Follow these steps to plot data in Giovanni: 1) Select a map plot type. 2) Select a date range. Data are in multiple temporal resolutions, so be sure to note the start and end date to ensure you access the desired dataset. 3) Check the box of the variable in the left column that you would like to include and then plot the data. For more information on choosing a type of plot, see the Giovanni User Manual.

Data, often in NRT, can be visualized in Worldview:

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Find Weather Maps

Find Weather Maps

NASA's Global Modeling and Assimilation Office provides applications for interactive analysis and visualizations of experimental, climatological data​, like this model of precipitation and sea level pressure for May 8, 2020.

NASA's Global Modeling and Assimilation Office provides applications for interactive analysis and visualizations of experimental, climatological data, like this model of precipitation and sea level pressure for May 8, 2020.

NASA's Global Modeling and Assimilation Office (GMAO) Goddard Earth Observing System, Version 5 (GEOS-5) model assimilates data from a variety of observations for each Earth System component. GEOS-5 has a series of weather maps which can be used to produce a 240-hour/10-day forecast of parameters, such as precipitation, humidity, wind speed, and temperature.

  • GEOS-5 Weather Maps
    Within the viewer, select the parameter or field of interest, the area of interest, and then indicate the forecast time and the forecast lead hour. Animate shows the forecast for the given parameter over the time period indicated. Note that it may take time to load the images to animate. For those variables near the surface, make sure to select 850 as your level.

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Find Socioeconomic Data

Find Socioeconomic Data

Global urban heat island dataset, from NASA's Socioeconomic Data and Applications Center (SEDAC), estimates the difference between land surface temperatures (LST) in urban areas and surrounding rural areas. LSTs are derived from Aqua MODIS 8-day composite LST data for a 40-day timespan.

Global urban heat island dataset, from NASA's Socioeconomic Data and Applications Center (SEDAC), estimates the difference between land surface temperatures (LST) in urban areas and surrounding rural areas. LSTs are derived from Aqua MODIS 8-day composite LST data for a 40-day timespan. Credit: SEDAC

Heat-related deaths are preventable, but prevention requires a knowledge of where vulnerable populations exist and what interventions are needed in those communities. For example, the urban heat island (UHI) effect represents the relatively higher temperatures found in urban areas compared to surrounding rural areas owing to higher proportions of impervious surfaces and the release of waste heat from vehicles and heating and cooling systems. In addition, socioeconomic status may limit a person's ability to mitigate extreme heat. Increasing frequency of heat events and other natural disasters may lead to migration and a change in population composition.

NASA's Socioeconomic Data and Applications Center (SEDAC) provides a number of datasets on population exposure and vulnerability.

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Tools for Data Access and Visualization

Tools for Data Access and Visualization

Earthdata Search | Panoply | Giovanni | Worldview | AppEEARS | MODIS/VIIRS Subsetting Tools Suite

Earthdata Search is a tool for data discovery of Earth Observation data collections from NASA's Earth Observing System Data and Information System (EOSDIS), as well as U.S and international agencies across the Earth science disciplines.

Users (including those without specific knowledge of the data) can search for and read about data collections, search for data files by date and spatial area, preview browse images, and download or submit requests for data files, with customization for select data collections.

Screenshot of the Search Earthdata site.

In the project area, for some datasets, you can customize your granule. You can reformat the data and output as HDF, NetCDF, ASCII, KML, or a GeoTIFF. You can also choose from a variety of projection options. Lastly, you can subset the data, obtaining only the bands that are needed.

Earthdata Search customization tools diagram.

Panoply

HDF and NetCDF files can be viewed in Panoply, a cross-platform application that plots geo-referenced and other arrays. Panoply offers additional functionality, such as slicing and plotting arrays, combining arrays, and exporting plots and animations.

Giovanni

Giovanni is an online environment for the display and analysis of geophysical parameters. There are many options for analysis. The following are the more popular ones.

  • Time-averaged maps are a simple way to observe the variability of data values over a region of interest.
  • Map animations are a means to observe spatial patterns and detect unusual events over time.
  • Area-averaged time series are used to display the value of a data variable that has been averaged from all the data values acquired for a selected region for each time step.
  • Histogram plots are used to display the distribution of values of a data variable in a selected region and time interval.

For more detailed tutorials:

  • Giovanni How-To's on NASA's GES DISC YouTube channel.
  • Data recipe for downloading a Giovanni map as NetCDF and converting its data to quantifiable map data in the form of latitude-longitude-data value ASCII text.

Worldview

NASA's EOSDIS Worldview visualization application provides the capability to interactively browse over 900 global, full-resolution satellite imagery layers and then download the underlying data. Many of the available imagery layers are updated within three hours of observation, essentially showing the entire Earth as it looks "right now." This supports time-critical application areas such as wildfire management, air quality measurements, and flood monitoring. Imagery in Worldview is provided by NASA's Global Imagery Browse Services (GIBS). Worldview now includes nine geostationary imagery layers from GOES-East, GOES-West and Himawari-8 available at ten minute increments for the last 30 days. These layers include Red Visible, which can be used for analyzing daytime clouds, fog, insolation, and winds; Clean Infrared, which provides cloud top temperature and information about precipitation; and Air Mass RGB, which enables the visualization of the differentiation between air mass types (e.g., dry air, moist air, etc.). These full disk hemispheric views allow for almost real-time viewing of changes occurring around most of the world.

Worldview data visualization of the nighttime lights in Puerto Rico pre- and post- Hurricane Maria, which made landfall on September 20, 2017. Post-hurricane image shows widespread outages around San Juan, including key hospital and transportation infrastructure.

Worldview data visualization of the nighttime lights in Puerto Rico pre- and post- Hurricane Maria, which made landfall on September 20, 2017. The post-hurricane image on the left shows widespread outages around San Juan, including key hospital and transportation infrastructure.

AppEEARS

AppEEARS, from LP DAAC, offers a simple and efficient way to access and transform geospatial data from a variety of federal data archives. AppEEARS enables users to subset geospatial datasets using spatial, temporal, and band/layer parameters. Two types of sample requests are available: point samples for geographic coordinates and area samples for spatial areas via vector polygons.

Performing Area Extractions

After choosing to request an area extraction, you will be taken to the Extract Area Sample page where you will specify a series of parameters that are used to extract data for your area(s) of interest.

Spatial Subsetting

Define your region of interest in one of these three ways:

  • Upload a vector polygon file in shapefile format (you can upload a single file with multiple features or multipart single features). The .shp, .shx, .dbf, or .prj files must be zipped into a file folder to upload.
  • Upload a vector polygon file in GeoJSON format (can upload a single file with multiple features or multipart single features).
  • Draw a polygon on the map by clicking on the Bounding box or Polygon icons (single feature only).

Select the date range for your time period of interest.

Specify the range of dates for which you wish to extract data by entering a start and end date (MM-DD-YYYY) or by clicking on the Calendar icon and selecting dates a start and end date in the calendar.

Adding Data Layers

Enter the product short name (e.g., MOD09A1, ECO3ETPTJPL), keywords from the product long name, a spatial resolution, a temporal extent, or a temporal resolution into the search bar. A list of available products matching your query will be generated. Select the layer(s) of interest to add to the Selected layers list. Layers from multiple products can be added to a single request. Be sure to read the list of available products available through AppEEARS.

Extracting an area in AppEEARS

Selecting Output Options

Two output file formats are available:

  • GeoTIFF
  • NetCDF-4

If GeoTIFF is selected, one GeoTIFF will be created for each feature in the input vector polygon file for each layer by observation. If NetCDF-4 is selected, outputs will be grouped into .nc files by product and by feature.

If GeoTIFF is selected, you must select a projection

Interacting with Results

Once your request is completed, from the Explore Requests page, click the View icon in order to view and interact with your results. This will take you to the View Area Sample page.

The Layer Stats plot provides time series boxplots for all of the sample data for a given feature, data layer, and observation. Each input feature is renamed with a unique AppEEARS ID (aid). If your feature contains attribute table information, you can view the feature attribute table data by clicking on the Information icon to the right of the Feature dropdown. To view statistics from different features or layers, select a different aid from the Feature dropdown and/or a different layer of interest from the Layer dropdown.

Interpreting Results in AppEEARS

Be sure to check out the AppEEARS documentation to learn more about downloading the output GeoTIFF or NetCDF-4 files.

MODIS/VIIRS Subsetting Tools Suite

ORNL DAAC also has several MODIS and VIIRS Subset Tools for subsetting data.

  • With the Global Subset Tool, you can request a subset for any location on earth, provided as GeoTiff and in text format, including interactive time-series plots and more. Users specify a site by entering the site's geographic coordinates and the area surrounding that site, from one pixel up to 201 x 201 km. From the available datasets, you can specify a date and then select from MODIS Sinusoidal Projection or Geographic Lat/Long. You will need an Earthdata Login to request data.
  • With the Fixed Subsets Tool, you can download pre-processed subsets for 3000+ field and flux tower sites for validation of models and remote sensing products. The goal of the Fixed Sites Subsets Tool is to prepare summaries of selected data products for the community to characterize field sites. It includes sites from networks such as NEON, ForestGeo, PhenoCam and LTER that are of relevance to the biodiversity community.
  • With the Web Service, you can retrieve subset data (in real-time) for any location(s), time period, and area programmatically using a REST web service. Web service client and libraries are available in multiple programming languages, allowing integration of subsets into users' workflow.

Directions for subsetting data with the ORNL DAAC MODIS and VIIRS subset tool

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Published July 29, 2020

Page Last Updated: Aug 6, 2020 at 2:01 PM EDT