Data Series #5: What the weather can and cannot say about climate

The Data Series continues with a look at trends in weather and what they can and cannot tell us about climate.

Helping us with this is David Vallee, the Hydrologist-in-Charge of the National Weather Service’s Northeast River Forecast Center in Taunton, Massachusetts. The center provides detailed forecasting information to National Weather Service Forecast Offices and the hundreds of federal, state and local water resource entities throughout the Northeast and New York. Mr. Vallee has also served as Science and Operations Officer and Hurricane Program Leader at the NWS Weather Forecast Office. Mr. Vallee is a graduate of Lyndon State College and is known for his outreach and education work on the behavior of New England Hurricanes, including many appearances on local radio and T.V. networks, the Weather Channel, the History Channel and the Discovery Channel.

NOAA's David Vallee

Mr. Vallee has also conducted research addressing severe storms, floods, heavy rainfall production, the behavior of New England Hurricanes, and most recently looking at the changing river flood behavior as a result of the combined effects of a trending climate (warmer/wetter) and urbanization over the past 40 years.

Catholic Ecology: There has been lots of talk about this or that extreme weather event being “proof” of climate change. What should people know about the differences and the links between weather and climate?

David Vallee: We must remember that day-to-day weather is just that—changeable on a day-to-day basis. Changes in a region's climate happens over time—often on time spans of decades. No one single event should be "blamed" on climate change. However, trends in the behavior of weather systems may be based on our changing climate.
   

CE: How would a warmer climate impact everyday weather or the seasons themselves?

Vallee: Over time, we would expect to see a short winter season, increased precipitation over the long term, and a continued reduction in sub-zero temperatures and an increase in temperatures exceeding 90 degrees. Keep in mind however that this doesn't rule out having a cold/snowy winter or a cool/damp summer from time to time. These types of events however have become less frequent. The trends across much of New England clearly suggest we are in a part of the country where annual precipitation is increasing, annual temperatures are increasing and season-to-season snowfall has become extremely variable from one season to the next.

CE: It does seem like there have been more storms here in the Northeast and across the USA and the globe. What does the data say about trends in precipitation and storm intensities?

Vallee: It is difficult to say explicitly that storm intensity has changed. Likewise, it is difficult to say the frequency of any particular type of major storm event has increased. But what we are seeing is that when these major storm systems develop they seem to packing more of a punch; more moisture, slower moving, more energy etc. Our region has seen this play out in a variety of ways. The March 2010 floods [in Southeastern New England] consisted of 4 major rain events in 5 weeks, influenced by El Nino and blocking high pressure to our north over Greenland. In a warming climate these types of blocked atmospheric flow regimes are expected to become more frequent. What this means in our region is that if we get stuck in a blocked pattern that has the storm track aimed at New England, we will see lots of precipitation, be it rain or snow.  

CE: Are there other trends you’re noticing that have you concerned?

Vallee: The combination of increased annual rainfall, the up-tick in heavy precipitation events, falling upon our urbanized small to moderately sized watersheds has me most concerned. A wetter regime means our lakes, reservoirs, and soils are wetter more often. Urbanization along some of the basins as limited their capacity to effectively move the water through the system. Increase the rainfall just a bit and you increase the risk for flooding. Similarly, the sea level rise on the coast is equally concerning. We have lost 150 to 250 ft or more of coastline since the 1938 hurricane. This does two things: it places more properties at risk for flooding from hurricanes and it sets us up for a weaker storm being capable of producing inundation along the coast that we would have expected to only happen from a stronger storm. I feel that to some degree, Sandy illustrated this along the Rhode Island coastline last October.

CE: How do recent storms in our area differ from what we may have seen in the past?

Vallee: Parts of the northeast [United States] are now experiencing storms that have more moisture to work with. I don't believe we are necessarily seeing an increase number of storms (nor'easters, hurricanes, etc.). That behavior change is what may be driving the increase in annual precipitation throughout the region. Similarly, prolonged cold snaps have become less frequent and this has resulted in a shift in the spring date when ice typically lets out of the interior rivers, results in a reduced duration of snow covered ground, and during the transition between winter and spring, can result in higher river flows from runoff prior to the start of the growing season.

Aftermath of Sandy along the Rhode Island coast. 

Photo RI DOT

CE: What else would you like people to know about recent weather trends and patterns, or possible future trends?

Vallee: Given the new regime we seem to be in, the questions in mind are focused on infrastructure; are we designed for this new "place" we find ourselves in?  This applies to the vulnerable coastline as well as our inland rivers and streams. Difficult choice lay ahead when it comes to land use, design criteria, local preparedness and mitigation efforts, etc. Even if we were to plateau [at current] trends and stay about where we are today, are we positioned to deal with these type of weather events to reduce their impacts, reduce the damages and the risks posed to the infrastructure, the business community, and our citizens? Time will tell.

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