John A. Callahan

Hi everyone! I am a Visiting Assistant Professor in the Department of Geography and Spatial Sciences at the University of Delaware, where I teach, advise students, conduct research, and provide service to the University community. (Well, at least I try to do all of those!) I received my PhD in Climatology and my MS in Geography from University of Delaware in Newark, DE, and BS degrees in Physics and Mathematics from Temple University in Philadelphia, PA.

I consider myself a Climate and Weather Scientist (that’s where my heart is, and my degrees), although my work generally has been multi-discipline. For example, much of my work includes meteorological and coastal processes, storms, water resources, salt marshes, natural hazards, climate change education, and human impacts, all of which all touch on meteorology, oceanography, geology, geography, policy, and planning disciplines. Technical methods have also played a large role in my work, such as GIS/GPS, remote sensing, spatial and time series statistics, multiple programming languages. (Check the other pages on this site for more details.) Sometimes this broad experience is a benefit; other times deep expertise on a narrow topic is needed. It’s a balance.

My previous position was an Associate Scientist with the Delaware Geological Survey (located on the UD main campus in Newark), where our primary mission was to provide scientific guidance to Delaware state and local governments, natural resource managers, citizens, and others related to the safety and well-being of all Delaware stakeholders. This included providing guidance in real-time during severe weather events, natural hazards impacting the state, and state/community long-term planning.

Just like many of those active in climate change work (scientists, planners, resource managers, policy experts, etc…), service-outreach-communication are all becoming more important components of my responsibilities. Maybe the most important parts. Serving on local or national committees, meeting with city groups and state/federal agencies, speaking to school students (in-person or through Skype a Scientist!), making public talks, and even posting on social media can all help. In the coming years, I’m expecting to do more in regard to public science education and emphasizing the importance of critical thinking skills (check out I’ll try to post outreach types of activities on my Outreach page.

There are a few particular past work activities I’m proud of: In 2002, my wife and I were lead in developing an early online, mapping application called the Delaware Data Mapping and Integration Laboratory (DataMIL). It was geared towards collaboration among state and federal providers of critical “spatial framework” datasets. We were invited to present this on the plenary stage of the ESRI User Conference with Jack Dangermond to approx. 12,500 attendees! In 2016, I was asked to present at the inaugural Delaware March for Science and our Earth event. I was the first climate scientist speaking and set the stage for the other presenters. Also around that time, I served as committee chair of the Delaware Sea-Level Rise Technical Committee and was lead author of our report, Recommendation of Sea-Level Rise Planning Scenarios for Delaware: Technical Report. That report was the recipient of the 2019 John C. Frye Memorial Award, jointly sponsored by the Geological Society of America and Association of American State Geologists.

Over the years, I’ve been parts of lots of projects and grant proposals. Some examples of recent projects include: storm tides/surges from tropical and mid-latitude storm systems in the Delaware and Chesapeake Bays, long-term rates of sea-level rise in the Mid-Atlantic, influence of teleconnections on weather and coastal flooding in the Mid-Atlantic, climate drivers of Atlantic White Cedar tree growth, assessing roads and communities vulnerability to flooding, quantifying uncertainties in lidar-based elevation in tidal salt marshes, and the Delaware Coastal Flood Monitoring System (, an early warning system for coastal flooding. Check out my Research page or CV for more details.

This is a new website for me and I am still unsure what (or how often) I’ll be able to post. Coming out of COVID, it’s especially difficult to estimate what the future holds. Feel free to reach to me via email or Twitter DM!