With climate change, rivers pose unique problems
While many people may be worried about change in sea levels and our coastline, David Vallee has a warning about our rivers.
Vallee, who grew up in West Warwick, is the hydrologist-in-charge at the National Weather Service’s Northeast River Forecast Center, and he recently gave a presentation to journalists and the public during the Metcalf Institute for Marine & Environmental Reporting to present his findings on drastic changes in Rhode Island rivers.
“We’re seeing changes in the behavior of our smaller rivers,” said Vallee, pointing out that changes in precipitation, temperature and landscape are all impacting river flooding.
“Our infrastructure is not designed to sustain this kind of rain,” added Vallee.
Vallee provided a list of various changes that are playing a role in the behavior of area rivers, such as increasing annual precipitation, increasing frequency of one- to two-inch rain events in a 24-hour period, warming temperatures, wildly varying season to season snowfall amounts, which is leading toward increased “well below normal” seasons, and a trend toward increased flood magnitude and/or frequency in smaller basins (less than 800 square miles).
Themes Vallee made mention of when it comes to major floods in the area are slow moving weather systems, multiple events and a tropical connection. The tropical connection is atmospheric rivers, often known as “tropical plumes,” which account for 90 percent of global water vapor transport. Vallee explained that there could be three to five of these water vapor rivers in the atmosphere at any given time.
“You get hit in succession,” said Vallee, pointing out that these plumes have the potential to combine with storm tracts and can lead to the massive flooding of the Pawtuxet River, similar to the event in March 2010. “We’re measuring contents of these plumes we’ve never seen before.”
Changes in temperature are not helping the situation either. Vallee pointed out that even modest temperature changes, in air or water, can lead to the atmosphere holding more moisture, and temperatures are changing dramatically in the area.
“We don’t see below zero temperatures anymore,” said Vallee, pointing out that the last 20 years have seen a clustering of the warmest years on record.
There has also been a clustering of wet years in recent history. According to Vallee’s presentation, for the past three and a half years, there has been an inch increase in average rainfall each year, measured at T.F. Green Airport.
Because there are more rain events, the ground is absorbing more water than it can handle. Then when another large rain event occurs soon after, the flooding begins. In addition to increased water events, the no rain events have lessened.
“Those events of drought have become more infrequent and less in duration,” said
The most concrete evidence Vallee presented was a chart depicting the number and intensity of flood events of the Pawtuxet since the 1940s. Prior to the construction of the shopping malls and I-95, the Pawtuxet flooded once and it was classified as a minor flood. Since 1968, the river has flooded 46 times, six of which were classified as major floods.
Vallee said he considers the area to have become a “hot spot” for record floods and heavy rainfall over the past 10 years due to increased yearly rainfall and an increased annual temperature.
In addition, Vallee says the Atlantic Ocean is getting warmer and therefore, there are expected to be a lot more hurricanes.
“Something is going on,” he said.
Looking forward now, Vallee says the rivers need to be modeled differently to account for these changes and steps need to be taken to protect the infrastructure from major flood events.
“The reality of the situation is we’re not built for what we’ve got,” said Vallee. “We have parts of our state’s infrastructure that are not designed for this type of reality.”
Vallee suggests moving some of the focus and concern for those living on the coastline to the rivers and building more intelligently.
“You have to look at the whole watershed,” he said.