Spatial Patterns in Summer Precipitation Changes across Complex, Mountainous Terrain in the Northeastern United States

Increases in summer precipitation can lead to lower attendance at parks and beaches and increase nutrient loadings into bodies of water, whereas decreases may reduce agricultural production and domestic water supplies. Across the northeastern United States, research has shown an increase in summer precipitation. However, much of this previous research utilized data that were spatially averaged over the entire region to get a broad sense of how precipitation has changed over time for regional and national climate assessments. To provide a station-by-station analysis of changes useful for local planning decisions, we examined gradual and abrupt changes in summer precipitation at twenty stations across a domain that encompassed complex, mountainous terrain in the northeastern United States that includes much of the White, Green, and Adirondack mountain ranges. Previous research has indicated that this region tends to have more spatial variability in the timing and magnitude of changes in precipitation. Our results highlight the spatial variability in gradual trends as well as in abrupt step changes over varying periods, allowing us to examine the influence of start year. Using the Pettitt changepoint test, we identified nine of the twenty locations that exhibited step increases significant at the 95% level. None of these stations exhibited the same changepoint, but the changepoints generally occurred in either the mid 1980’s or early 2000’s, with a few outliers. The twenty stations examined also had varying gradual trends in precipitation, though most exhibited a statistically significant increasing trend, consistent with previous research. We also briefly discuss changes in the variability of summer precipitation.