Category Archives: Extreme weather

Remote Sensing Shows the Extent of Flooding from Hurricane Harvey and Other Large Flooding Events

Dartmouth Flood Observatory, at the University of Colorado, Boulder, CO, integrates international satellite data to develop a worldwide view of surface water issues, and can provide regional maps that show the extent of flooding in areas of interest. Data from many satellite sources are used, including NASA’s MODIS (Moderate Resolution Imaging Spectrometer) and Landsat, European Space Agency’s (ESA) Sentinel 1, ASI (Agenzia Spaziale Italiana) Cosmos-SkyMed, and Canadian Space Agency’s Radarsat 2.

The Dartmouth Flood Observatory homepage is here:

http://floodobservatory.colorado.edu

The world view of large flooding events as of 26 August 2017 is shown in the graphic.

Source: Dartmouth Flood Observatory

The following 31 August 2017 maps show the areas in Texas and Louisiana that were flooded by Hurricane Harvey also known as DFO flood event 4510). Red represents flooded areas, blue represents normal water extent, and dark grey represents urban areas.

Area mapSource: Dartmouth Flood Observatory

Here’s the link to these detailed flooding maps for Hurricane Harvey:

http://floodobservatory.colorado.edu/Events/2017USA4510/2017USA4510.html

This webpage also provides links to other information sources related to Hurricane Harvey.

The Dartmouth Flood Observatory maintains an archive of large flood events from 1985 to present. This archive is accessible online at the following link:

http://floodobservatory.colorado.edu/Archives/index.html

Dartmouth Flood Observatory is a member of the Global Flood Partnership (GFP), which describes itself as, “a cooperation framework between scientific organizations and flood disaster managers worldwide to develop flood observational and modeling infrastructure, leveraging on existing initiatives for better predicting and managing flood disaster impacts and flood risk globally.” For more information on the Global Flood Partnership, visit their homepage and portal at the following links:

https://gfp.jrc.ec.europa.eu/about-us

http://portal.gdacs.org/Global-Flood-Partnership

Is it Possible to Attribute Specific Extreme Weather Events to Global Climate Change?

On 7 September 2016, the National Oceanic and Atmospheric Administration (NOAA) reported that climate change increased the chance of record rains in Louisiana by at least 40%. This finding was based on a rapid assessment conducted by NOAA and partners after unusually severe and prolonged rains affected a broad area of Louisiana in August 2016. You can read this NOAA news release at the following link:

http://www.noaa.gov/media-release/climate-change-increased-chances-of-record-rains-in-louisiana-by-at-least-40-percent

NOAA reported that models indicated the following:

  • The return period for extreme rain events of the magnitude of the mid-August 2016 downpour in Louisiana has decreased from an average of 50 years to 30 years.
  • A typical 30-year event in 1900 would have had 10% less rain than a similar event today; for example, 23 inches instead of 25 inches.

NOAA notes that “return intervals” are statistical averages over long periods of time, which means that it’s possible to have more than one “30-year event” in a 30-year period.

NOAA Lousiana Aug2016 extreme rain graphSource: NOAA

In their news release NOAA included the following aerial photos of Denham Springs, Louisiana. The photo on the left was at the height of the flooding on August 15, 2016. The photo on the right was taken three days later when floodwaters had receded.

NOAA Lousiana Aug2016 extreme rain photosSource: NOAA / National Geodetic Survey

World Weather Attribution (WWA) is an international effort that is, “designed to sharpen and accelerate the scientific community’s ability to analyze and communicate the possible influence of climate change on extreme-weather events such as storms, floods, heat waves and droughts”. Their website is at the following link:

https://wwa.climatecentral.org

WWA attempts to address the question: “Did climate change have anything to do with this?” but on their website, WWA cautions:

“Scientists are now able to answer this for many types of extremes. But the answer may vary depending on how the question is framed……..it is important for every extreme event attribution study to clearly define the event and state the framing of the attribution question.”

To get a feeling for how they applied this principal, you can read the WWA report, “Louisiana Downpours, August 2016,” at the following link:

https://wwa.climatecentral.org/analyses/louisiana-downpours-august-2016/

I find this report quite helpful in putting the Louisiana extreme precipitation event in perspective. I object to the reference to “human-caused climate change,” in the report because the findings should apply regardless of the source of the observed change in climate between 1900 and 2016.

On the WWA website, you can easily navigate to several other very interesting analyses of extreme weather events, and much more.

The National Academies Press (NAP) recently published the following two reports on extreme weather attribution, both of which are worth your attention.

The first NAP report, “Attribution of Extreme Weather Events in the Context of Climate Change,” applies to the type of rapid assessment performed by NOAA after the August 2016 extreme precipitation event in Louisiana. The basic premise of this report is as follows:

“The media, the public, and decision makers increasingly ask for results from event attribution studies during or directly following an extreme event. To meet this need, some groups are developing rapid and/or operational event attribution systems to provide attribution assessments on faster timescales than the typical research mode timescale, which can often take years.”

NAP Attribution of Severe Weather Events  Source: NAP

If you have established a free NAP account, you can download a pdf copy of this report for free at the following link:

http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-of-climate-change

The second NAP report, “Frontiers of Decadal Climate Variability,” addresses a longer-term climate issue. This report documents the results of a September 2015 workshop convened by the National Academies of Sciences, Engineering, and Medicine to examine variability in Earth’s climate on decadal timescales, which they define as 10 to 30 years.

NAP Decadal Climate Variation   Source: NAP

This report puts the importance of understanding decadal climate variability in the following context:

“Many factors contribute to variability in Earth’s climate on a range of timescales, from seasons to decades. Natural climate variability arises from two different sources: (1) internal variability from interactions among components of the climate system, for example, between the ocean and the atmosphere, and (2) natural external forcing (functions), such as variations in the amount of radiation from the Sun. External forcing (functions) on the climate system also arise from some human activities, such as the emission of greenhouse gases (GHGs) and aerosols. The climate that we experience is a combination of all of these factors.

Understanding climate variability on the decadal timescale is important to decision-making. Planners and policy makers want information about decadal variability in order to make decisions in a range of sectors, including for infrastructure, water resources, agriculture, and energy.”

While decadal climate variability is quite different than specific extreme weather events, the decadal variability establishes the underlying climate patterns on which extreme weather events may occur.

You can download a pdf copy of this report for free at the following link:

http://www.nap.edu/catalog/23552/frontiers-in-decadal-climate-variability-proceedings-of-a-workshop

I think it’s fair to say that, in the future, we will be seeing an increasing number of “quick response” attributions of extreme weather events to climate change. Each day in the financial section of the newspaper (Yes, I still get a printed copy of the daily newspaper!), there is an attribution from some source about why the stock market did what it did the previous day. Some days these financial attributions seem to make sense, but other days they’re very much like reading a fortune cookie or horoscope, offering little more than generic platitudes.

Hopefully there will be real science behind attributions of extreme weather events to climate change and the attributors will heed WWA’s caution:

“…it is important for every extreme event attribution study to clearly define the event and state the framing of the attribution question.”