From hot to cold, rainy to dry, the weather in New Hampshire can change in the blink of an eye.
Last summer, for example, saw record-breaking heat. This year, meteorologists predict lower temperatures, but more precipitation. That high variability is mainly a result of New Hampshire’s geography, among other factors.
New Hampshire sits at a confluence of storm tracks, said state climatologist Mary Stampone. Weather conditions in the state are influenced by air coming from three different areas: air coming from the northwestern Atlantic Ocean; warmer, more humid air coming up from the south; and drier air coming from the west.
“That kind of controls that high variability that we have day to day as well as year to year,” she said.
But even within such variability, scientists are able to pick up strong signals that point to the impacts of climate change. As humans continue to burn fossil fuels at record rates, those emissions put additional energy into the atmosphere, Stampone says. That amps up these weather processes, which can make extremes more frequent.
“So the hotter weather gets hotter, the wetter weather gets wetter, the drier weather gets drier,” she said.
In other words: While variability is a natural weather phenomenon, especially in New Hampshire, the intensification of extreme weather patterns across time has been defined by climate change.
So Stampone looks at how extreme weather has evolved throughout the years. For example, the number of days above 90 degrees and the number of nights above 70 degrees. Those temperatures are becoming more common in New Hampshire.
“That's going to move that average up over time in a way that we can track and statistically say, this is a temperature that we would not get without climate change,” Stampone said.
Overall, New Hampshire is becoming hotter and wetter. That trend brings a whole set of challenges, but Stampone highlighted the need to prepare for drought and constrained water supplies.
Precipitation rates in the state are rising, but they are mostly concentrated during winter months. During the summer, New Hampshire is not necessarily getting more rain. But instead of being spread out, rainfall now comes in more extreme individual events. This means there can be longer, drier periods between precipitation events, contributing to drought conditions.
“Soils will dry out in between,” Stampone said. “And then if you get all of that rain out once more, it is likely to run off over the surface, as opposed to soaking in and replenishing our groundwater systems.”
Those conditions could also impact the state’s water supply systems.
“Even though we're getting more water, it's going to be more concentrated in one season. And then there's another season where we need more water. It might not always be there,” Stampone said.
