Temperature and precipitation trends in the U.S. from 1931–2000
WEIHONG FAN, COLLEEN CAROLL, RICHARD STOCKTON COLLEGE OF NEW JERSEY, USA
Abstract: Climatic trends of mean annual temperature and annual precipitation from 1931 to 2000 are analyzed for four regions of the United States: Northeast, South Atlantic, North Central, and Pacific West regions. Climatic variations are known to obscure trend detection. To reduce the impact of outliers and variation, five-year moving averages are calculated for the trend analysis. Simple regression analysis was performed to evaluate the level of significance for each trend line. A trend with P < 0.0001 is considered statistically significant throughout the study. The data of five–year moving average temperature show a significant positive trend in the Pacific West with a R2 of 0.36 and significance F equal to 1.07E-07. Mean annual temperature of the Pacific West has increased by 0.62oC from 1931 to 2000. No significant trend is observed in any of the other three regions. The data of five-year moving average precipitation show a significant increasing trend in North Central Region of the U.S. with a R2 of 0.35 and significance F value of 2.87E-07. Annual precipitation of North Central Region has increased by 10.4 centimeters from 1931 to 2000, which is 10% higher than the long term average of the region. No precipitation trend is evident in any other region studied. Although 0.62oC of temperature increase may not be dramatic, it suggests that Pacific West may be experiencing the effect of global warming because this finding is consistent with the result of the Canadian climatic trend study by Zhang et al. (2000). They found that the temperature of southwest region of Canada has increased between 0.5 and 1.5oC in the past century. They also found that the annual precipitation has increased by 35% in southern Canada over the same period, which coincides with the increasing trend of precipitation we found in North Central Region of the U.S. With the best available data in this study and others, we are fairly confident that western United States is experiencing a significant warming trend. This trend is likely linked to the increasing sea surface temperature (SST) of the Pacific Ocean (Zhang and Levitus 1997, Karnauskas et al 2009).
Keywords: Global warming, climatic change, temperature trend, precipitation trend.