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ASU climatologist says trio of hurricanes might just be bad coincidence

September 13, 2017

ASU professor's research is on extreme weather; says recent powerful storms don't necessarily point to climate change

Arizona's official climatologist says she thinks the recent trio of hurricanes Harvey, Irma and Jose may simply be a terrible and unfortunate coincidence and is not necessarily a result of global warming.

Nancy Selover, a professor in ASU's School of Geographical Sciences and Urban PlanningThe School of Geographical Sciences and Urban Planning is a unit of the College of Liberal Arts and Sciences., focuses on extreme weather in her research. Selover educates groups around Arizona on climate topics, including urban heat islands, monsoons, drought, climate change and Arizona's climate more generally. She recently spoke to ASU Now about one of the most devastating hurricane seasons in decades.

Woman in blue shirt
Nancy Selover

Question: Are these three hurricanes occurring so close to each other a rare coincidence or a harbinger of things to come?

Answer: I think it’s a rare coincidence. We typically see hurricanes follow each other moving into the Caribbean, particularly at the peak of the season (which is now). One of these formed in the Gulf and the other formed in the Caribbean, and both benefitted from extremely warm water, which is required to get to Category 5, among other factors.

Q: So is this not a result of global warming as others in academia have claimed?

A: I don’t think this is a result of global warming as we have had many storms more powerful than these prior to 1960, including many Category 5 and 4 storms. We tend to focus on the most recent storms as being worse than historical storms because we have so much coverage of them and a larger population that puts itself in the path of the storms. The probability of a major hurricane making landfall anywhere on the Gulf or Atlantic coast is exactly the same as it was 100 years ago. What is not the same is that 100 years ago the number of people at risk by being in the path was at least one order of magnitude smaller.

Q: Do you predict hurricanes will become stronger and more powerful in the future? 

A: It’s been 12 years since Katrina and Rita, and it has been relatively quiet since then, other than Sandy, which was very different in its path and timing and was at the end of the season. Sandy was not even a hurricane when it came ashore, so I think it’s important to remember that any tropical storm has the capacity to devastate a coastal community. If the ocean waters become warmer, the available energy for major hurricanes increases, but warm water is not the only condition necessary for forming, strengthening or sustaining a hurricane. If it were, then Jose would have followed Irma as a Category 4 or 5.

Q: Any other types of weather-related disasters you think might be coming our way? 

A: If the warmer waters of the eastern Pacific, western Atlantic and Gulf of Mexico are sustained, more evaporation will occur and we will have the potential for heavier rain (or snow) events due to the increased moisture. It would be nice if it came in the winter as snow. But for the past few years, it has been adding to the monsoon moisture resulting in some heavier rain events, which lead to local flash flooding.

Q: What are preventive measures that we as a society can do to ensure the longevity of our planet? 

A: That’s an impossible question to answer as the planet will be fine regardless of what we do. I think the longevity of ourselves and the ecosystems are of more concern. The Earth has changed drastically over hundreds of millions of years and will continue to do so, with or without us.  

Q: What type of natural disasters might Arizona be facing one day? 

A: We have earthquakes, though small, and our volcanic activity is probably behind us. Our weather-related disasters will continue to be the same ones we currently have: winter storms, heavy rain or rain-on-snow leading to flooding, drought and wildfires. We aren’t likely to have hurricanes, though we do get the remnants of tropical storms mixed into the monsoon. We do have tornadoes, but typically only EF3 or smaller, and even the very small ones are rare. I don’t expect that will change. Because we are an arid state, we have so much variability already in our weather that we do a much better job than most places in handling that variability.

 
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Mapping out the next steps after natural disasters on coastlines

September 13, 2017

ASU geophysicist creates maps from satellite data for first responders during emergencies and policy makers for long-term planning

Knowing the lay of the land is crucial for first responders during emergencies and for civic planners making decisions that direct a city's future. Natural disasters, however, have a way of drastically and suddenly changing that land.

Manoochehr Shirzaei, a geophysicist and radar remote sensing expert at Arizona State University's School of Earth and Space Exploration, specializes in satellites equipped with instruments that use highly accurate remote sensing, called Synthetic Aperture Radar. The data collected from these satellites allow Shirzaei to create high-resolution images of the Earth, with an emphasis on identifying sinking lands and flood zones. The maps are then provided to first responders as well as to public policy makers for long-term planning.

Question: What is a geophysicist, and how does that field relate to flooding caused by hurricanes like Harvey and Irma?

Answer: Geophysics is the study of the physical processes and physical property of Earth (and its surrounding space environment) by mapping the variations of physical property that are remotely sensed. In my case, I’m using satellites to study the Earth’s surface and specifically ground-level changes, which can be the result of natural causes or human-caused ones like extraction for water or fuel. 

Q. You created a map of the Houston area with flooding caused by Hurricane Harvey (the map is pictured above, with flooded areas in red). How was this map created?

A: We acquired data from the Sentinel 1A/B satellites that belong to the European Space Agency. The instruments on these satellites use radar to provide highly accurate remote sensing data. There are two satellites that have a six-day revisit time (orbiting the Earth every six days), so we can compare an area before and after a disaster. 

The raw images at first look like black and white dots, as if you were to spread large amounts of salt and pepper over a sheet of paper.  Once we’ve processed the data, we can colorize the mapped areas based on levels of flooding. 

See a larger version of the map here.

Q: How will the map be used?

A: During an intense storm, it is difficult to fly an airplane or drone over an affected area. And then clouds often are in the way of any satellite pictures that would show us what the flooding may look like. But radar can get through both clouds and rain.

This is helpful for first responders so they can determine where aid and relief is needed the most. It can also help with estimating the overall damage of an area. 

In terms of forecasting, remote sensing is also useful to determine which land is above or below sea level and therefore more prone to flooding. 

A map showing areas flooded in Florida after Hurricane Irma
A map of southeast Florida flooding caused by Hurricane Irma generated from two C-Band SAR images acquired by Sentinel 1A/B satellites between Aug. 28 and Sept. 10. Image by Manoochehr Shirzaei

Q: And how did you create a similar map for the flooding caused by Hurricane Irma?

A: I contacted the European Space Agency in advance of the storm hitting Florida and requested data from their Sentinel 1A/B satellites. Once the storm hit and the data were available for the affected area, I began creating maps depicting the areas of flooding along the Florida coast. These maps are then provided to the appropriate local and national authorities so they can better assist those areas in need. 

Q: You recently were recently selected to join the NASA Sea Level Change Team. What will you be doing for NASA as part of this team?

A: I will be working on mapping the U.S. coasts and studying the coastal land subsidence as well as the impact of sea-level rise on coastal flooding. NASA will use this data to inform local and national public authorities so that they can plan for flooding and infrastructure improvements, with the goal to minimize future damage.  

 

Top photo: Map of Houston flooding caused by Hurricane Harvey generated from two C-Band SAR images acquired by Sentinel 1A/B satellites between Aug. 24 and 30. Image by Manoochehr Shirzaei

Karin Valentine

Media Relations & Marketing manager , School of Earth and Space Exploration

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