New Hampshire Precipitation Patterns 2005–2009: A Climatological Perspective

The years 2005 through 2009 have been some of the wettest on record for the state of New Hampshire and many residents are concerned that this trend will continue indefinitely. However, this recent wet period is not entirely unique within New Hampshire's climatological record. Statistical analysis of total annual precipitation for nine New Hampshire stations, each dating from at least 1890 to the present, indicate that similar wet periods (1897-1902, 1936-1938, and 1951-1954) have occurred throughout each record. Periods characterized by above average precipitation typically ranged in duration from three to five years followed abruptly by extended periods (five to fifteen years) of normal to below normal precipitation. This pattern dominates the time series prior to 1970, when a pattern of high inter-annual variability emerges and continues through the early 1990's. Over the past 15 years, the variability in total annual precipitation between consecutive years decreased compared to the 1970 to 1990 period. Correlation functions also indicate a greater similarity between the recent pattern of inter-annual variability and that observed prior to 1970, indicating a possible return to a more predictable pattern of multi-year wet and dry periods for New Hampshire.