Data Homogenization and Analysis of
Climatic Extremes in the Northeast United States

Michael Griffiths

M.S. Candidate

Advisor: Raymond Bradley

The Northeast region of the United States is home to some of the most extreme and variable weather and climate in the world. This includes extremes of both high and low temperatures, droughts, heavy rainfall, hurricanes, tornadoes, blizzards, and more. These great variations of weather and climate in this region are influenced by many factors related to the physical geographical setting, including the region’s latitude and coastal orientation (Keim, 1998).
Mean annual temperature (MAT) varies substantially across the northeast. The coldest locations are in northernmost Maine, whereas the southern parts of Pennsylvania and New Jersey are the warmest. Mean annual precipitation varies from about 890 mm in the more interior part of the region to over 1270 mm along some coastal areas. Greater seasonality of temperature (higher summer and lower winter temperatures) is a function of the degree of continentality of the climate. A greater annual range occurs in the interior-most parts of the region (Zielinski and Keim, 2003).
Climate in the northeast region of the United States has varied substantially over the past two centuries. This time period was characterized by the end of the so-called “Little Ice Age” and the onset of a warming trend, in the twentieth century that is most likely a result of anthropogenic increases in greenhouse gases (IPCC, 2001). In addition, some of the warmest and coldest, plus wettest and driest, periods of the past millennium have been recorded during this time interval. These periods of changing climate have been recorded by both instrumental records (which extend back to the late 18th century in some areas) and also by natural proxies. These proxies include pollen records and, more commonly, tree-ring records.

Study Area
The area of study (Fig. 1), which is located in the northeast quadrant of the United States, includes the six New England states (Maine, New Hampshire, Vermont, Massachusetts, Connecticut, and Rhode Island) as well as three nearby states (New York, Pennsylvania, and New Jersey). The study area extends from 38° 55’ N to 47° 22’ N and from 67° 15’ W to 80° 30’ W and ranges in elevation from sea level to 1,917 meters (summit of Mount Washington). Topographically, this region is partly delineated from the rest of the nation by the Appalachian Mountains to the west. From the Green Mountains, the White Mountains, and Berkshire Hills, the land surface slopes gradually toward the Atlantic Ocean.

Figure 1. Location of the study area. The region comprises the six New England states (Maine, New Hampshire, Vermont, Massachusetts, Rhode Island and Connecticut) and three adjacent states (New York, New Jersey and Pennsylvania).

In this study my objectives are as follows:
• Create a database of long term instrumental monthly climate data (temperature, precipitation) from as many stations as possible in the study area, which have a period of record that           extends at least thirty years into the 19th century. This data will be compiled from a variety of online sources.
• Analyze and adjust these instrumental climate data for inhomogeneities using a variety of statistical techniques.
• Obtain a small network of daily records for the study area and use this data to identify episodic climate extremes based on a set of climatic extreme parameters developed by the European Climate Assessment (ECA) group.
• Examine the frequency and intensity of extreme climatic events (e.g. extreme cold events) related to natural processes (e.g. volcanic events), and modes of large-scale atmospheric circulation (e.g. ENSO, PDO, NAO).

Climate Extremes
A large set of climatic extreme indicators were developed by the European Climate Assessment (ECA) group following a set of global meetings. The rationale for the development of these indicators was to provide the base line data for evaluating climate change scenarios worldwide in the future. This large list was refined to 10 extreme indicators (nine are used in this study) by Frich et al (2002), all of which could be applied to a large variety of climates. The indicators are based on daily minimum and maximum temperature series, as well as daily totals of precipitation, and represent changes in all seasons of the year. For a full list of all the ECA indicators and for full descriptions used in this study refer to the ECA website at .

The extreme indicators associated with temperature include:
i) Frost Days (FD): measures air frosts, which will sample the winter half year in all extra-tropical regions, particularly the beginning and end of the cold season.
ii) Intra-annual Extreme Temperature Range (ETR): will span the most extreme high temperature event of the summer season and the most extreme low temperature event of the winter season.
iii) Heat Wave Duration Index (HWDI): samples the daytime maxima throughout the year in most climates.
iv) Tn90: is the percent of observations exceeding the daily 90th percentile for the 1961-1990 base-periods, which will sample primarily the warm nights during the year.
v) Length of the thermal Growing Season Length (GSL): will sample spring and fall anomalies in the higher latitudes (Frich et al., 2002).

The extreme indicators associated with precipitation include:
i) The maximum number of Consecutive Dry Days (CDD): This will potentially be a valuable drought indicator for the dry part of the year.
ii) R10: The number of days with precipitation > 10mm.
iii) The Simple Daily Intensity Index (SDII): This will summarize the wet part of the year.
iv) R5d: The greatest 5 day precipitation total of the year: This will represent some of the more extreme precipitation events of the year (Frich et al, 2002).
v) R95T: Fraction of annual total precipitation due to events exceeding the 1961-90 95th percentile.

The proposed research will generate a high quality dataset that will help to resolve current uncertainties associated with climate extremes in New England and adjacent states from the late 19th century to present. Climate extremes play an integral role in everyday life for people not only in the northeast United States, but all around the world. If we can better understand the relative periodic patterns of climate extremes in the past for the region, we can gain a clearer understanding of future patterns of climate extremes, and also assess the linkages between these extremes and other periodic modes of climatic variation such as ENSO, NAO and PDO. In addition, these climate extremes may be linked to natural events such as volcanic events and variations in solar radiation, as well as anthropogenic forcing mechanisms.
In addition to the assessment of these climate extremes, the adjusted instrumental data will be used to create a spatially and temporally detailed 19th century climate database for New England and adjacent states, in a NOAA funded project involving R.S Bradley (University of Massachusetts), A. Kaplan (Lamont-Doherty Earth Observatory) and G.A. Zielinski (University of Maine). In this project, complementary sets of instrumental and historical data will be used to provide a comprehensive network of 19th century data for the region.

Frich, P., L.V. Alexander, P. Della-Marta, B. Gleason, M. Haylock, A.M.G. Klein, and T. Peterson, 2002: Observed Coherent changes in climatic extremes during the second half of the twentieth century. Climate Research, 19:193-212.

IPCC (2001) Climate Change 20001: the Scientific Basis Contribution of Working Group I to the third Assessment Report on the Intergovernmental Panel on Climate Change. J.T.

Keim, B., 1998: Extreme Climatic Events in New England History. New England’s Changing Climate, Weather, and Air Quality,

Zielinski, G.A., and B.D. Keim, 2003: Seasons of New England, New England Weather, New England Climate, CH 11, p124. University Press of New England.

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