Academic journal article Southeastern Geographer

A Comparison of 30-Yr Climatic Temperature Normals for the Southeastern United States

Academic journal article Southeastern Geographer

A Comparison of 30-Yr Climatic Temperature Normals for the Southeastern United States

Article excerpt

Thirty-year climatic normals are an integral part of climate and climate assessment, but they are typically not used to address issues of climatic change. For 104 stations within the southeastern United States, I analyze spatial parameters of the two most recent 30-yr temperature normals (1961-1990, 1971-2000) to illustrate the utility of 30-yr normals for an assessment of climatic change. My comparison of the two normal periods shows that the Southeast as a whole has experienced a small (0.10[degrees]C) but significant increase in average temperature. However, of the seven physiographic provinces examined, only the lower Coastal Plain has experienced a significant increase in temperature. My analysis of urban versus rural sites produced mixed results on the potential impacts of urbanization and the associated heat island effects on the observed changes in temperature. While some long-term analyses of the thermal climate of the Southeast have shown the region to be cooling, my results suggest that the thermal climate of the southeastern United States since 1961 is stable or slightly warming.

KEY WOADS: climatic normals, temperature, southeastern U.S., climate change

INTRODUCTION

Thirty-year normals have been a mainstay in climatology since the U.S. Weather Bureau adopted them during the 1950s in response to World Meteorological Organization guidelines (Lamb and Changnon 1981), The 30-yr climatic normals are updated each decade to reflect the most recent period of record (e.g., current normals are calculated using data from 1971-2000) (NCDC 2004a). In turn, moving averages associated with these periodic updates can impact analyses and perceptions of climate through interpretations of the deviations from normal. For example, deviations from normal are a standard element of the monthly NOAA publication "Climatological Data" (NOAA 2003) for each state and they are incorporated into forecasts provided by many media outlets to help place the current day's weather into historical perspective. Most studies use, at minimum, annual data to address questions related to changing climatic conditions (e.g., Karl et al. [1996] use various annual indices, Knappenberger, Michaels, and Davis [2001] use daily data). While 30-yr normals are useful both for instructive purposes (e.g., maps showing regional conditions) and for practical purposes (e.g., they are often incorporated into load forecasting models used by the electric power generation industry [Meentemeyer and Soule 1989; Meentemeyer, Soule, and Bland 1990]), they are generally not used to directly test changing climatic conditions. The purpose of this study is to show how 30-yr climatic normals can be used to assess changes in climate within the thermal regime of the southeastern United States. I use the two most recent 30-yr normal periods (1961-1990, 1971-2000) to: (1) determine if thermal conditions have remained stable through time, (2) examine the spatial pattern of any observed changes, and (3) assess the possible role that site selection (i.e., urban versus less urban/rural) plays in the determination of significant changes in climate.

The southeastern United States is somewhat anomalous in climate change research as most analyses show this area did not warm significantly during the twentieth century (e.g., Karl et al. 1996; Greenland 2001; NCDC 2004b). For example, while linear trends showed as much as 3[degrees]C of warming for much of the United States, temperatures in the Southeast largely exhibited cooling trends of 1-2[degrees]C for the period 1900-1994 (Karl et al. 1996). Over a shorter time period (1948-1994), Saxena and Yu (1998) also found downward trending temperatures in the Southeast. Analyzing temperature data from a small sample of sites (n = S) across the Southeast, Greenland (2001) found no long-term (i.e., 1900-1997) trends in temperature, but rather a non-monotonic pattern with warming until mid-century, followed by cooling to about 1975 and then warming through 1999. …

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