Hydroclimatological and geomorphic controls on the timing and spatial variability of floods in New England, USA

Numerous methods exist to express a region's flood regime, but because of the various controls on flooding, no salient method emerges. We have used directional (also known as orientation) statistics to express some of the hydroclimatological and geomorphic controls on flooding in New England and mapped these statistics for 36 gages to reveal the regional groupings of similarly responding basins. Directional statistics express the temporal variance of flood timings and characterize the seasonality of floods, and thus begin to demonstrate some of the climatic controls on flood timing and their spatial effects. Contour maps of the vector mean timing of floods indicate the strong control of coastal influences on the hydrologic regime, and multiple regression analyses indicate that both the surrogate variables for climate, latitude and distance to the coast, strongly explain the timing of the vector mean, although both the geomorphic variables, basin size and altitude, are also significant explanatory variables. An autumnal flood season exists along coastal locations but disappears moving both inland and northward through the region. For many of these coastal locations (especially in the south), the autumn mode reflects the occurrence of hurricane-induced floods which for many basins represent the largest flood in the annual series. The strength of the seasonality, as expressed by the mean resultant magnitude, is controlled primarily by basin size with distance to the coast and altitude also important. Finally, these results suggest that directional statistics are an appropriate method for depicting regional hydrologic regimes and in describing some of the hydroclimatological controls on flood occurrence.