Climate Change in the Champlain Basin - The Nature Conservancy

What natural resource managers can expect and doIII. MethodsClimate, or the “climate normal” for a particular location, is typically defined as the average weather conditionsover a period of 30 years, a sliding window of time that is updated from year to year. For the purposesof this report only two climatic factors—temperature and precipitation—will be discussed in detail. Otherfactors, such as wind and humidity, are potentially important as well, but they are less thoroughly documented andare beyond the scope of this study. Table 1 summarizes mean climatic conditions in the Champlain Basin between1976 and 2005, based upon records from eight weather stations in the watershed.Table 1. Temperature and precipitation in the Champlain Basin 1976–2005, averagedfrom eight USHCN weather stations in the watershed.ChamplainBasin 30-yr*Annual(J-D)Winter(DJF)Spring(MAM)Summer(JJA)Autumn(SON)Mean T (°F) 44.5 19.2 42.2 65.8 46.4Mean P (in.) 37.5 6.3 8.6 11.9 10.8* J-D is a full year, January through December; DJF is December, January, February;MAM is March, April, May; JJA is June, July, August; SON is September,October, November.In order to determine how climatic patterns within the ChamplainBasin have changed in the recent past, we analyzedlocal weather records from the United States Historical ClimatologyNetwork (USHCN). Most weather datasets containflaws due to gaps in coverage, changes in instrumentation,and inconsistencies in the number and timing of daily observations.Simply using their raw data for analysis thereforeproduces spurious results. The USHCN performs standardizedadjustments that fill temporal gaps and that compensatefor changes in methodology, urban development and othersuch biases (Menne and Williams, 2005, 2009; Menne et al.,2009). The database currently includes records from morethan 1,200 stations in the lower 48 states, and it is producedand updated at the National Climatic Data Center in conjunctionwith the Department of Energy’s Carbon Dioxide InformationAnalysis Center.The eight USHCN stations located within the ChamplainBasin are indicated on Map 2 and are also listed in Table2, along with mean annual temperatures and total annualprecipitation measured at each station for two time frames:the entire period of record (1895–2008) and a recent 30-yeartime interval (1976–2005) that has been selected for comparisonto previous studies in the region. For our analyses, therecords were averaged together to produce mean values forthe basin as a whole. Trends were calculated through linearregression (Press et al., 1986) with the SigmaPlot TM program,using p-values of up to 0.05 to indicate statistical significance.Map 2. The eight United States HistoricalClimatology Network weather stations locatedin the Champlain Basin.Map by D. Farrell, The Nature Conservancy, Vermont Chapter7