Climate and Energy Action Plan (CEAP)

CLIMATE TRENDS & PRO JECTIONS | CITY OF ASHLAND, OREGON | FINAL REPORT | 33 Full Description of Data Sources & Analysis Methods Historic Trends Observed trends in annual and seasonal tempe rature and precipit ation were analyzed from 1893 to 2014 using monthly data from the United States Historical Climate Network Version 2.5 (USHCNv2.5) downloaded from the Carbon Dioxide Inf ormation Analysis Center website for the station in Ashland (350304) located at 42.2128°N and -122.7144°E at an elevation of 532.2 meters. The USHCN is a subset of the National Weather Service Cooperative Observer Program network . While there are several weather stations in the vicinity of Ashland, the USHCN station was selected for its length of record and data completeness. In addition , the USHCN stations have be en quality controlled and bias -corrected to remove non -climatic influences such as site moves, canopy changes, and instrumentation changes (Menne et al., 2009) . They provide the best quality data for long -term trend analysis. Monthly data of temperature and precipita tion were aggregated for winter (December, January, and February ), spring ( March, April, and May ), summer ( June, July, and August ), fall (September, October, and November ), and annually for the analysis. Annual an d seasonal trends in maximum, mean, and minimum temperature and total precipitation were estimated over the period 1893 - 2014. Observed trends in April 1 snow water equivalent (SWE) were analyzed using SNOTEL and Snow Course data collected by the Natural Resou rces Conservation Service . Trends were e stimated over the period 1960 -2014 (Mote & Sharp, 2014) for 13 stations in the Rogue Basin, mostly located within the Upper Rogue sub -basin along the western slopes of the Cascade Mountains. SNOTEL sites began recording data in the 1980s, so NRCS uses data from existing Snow Course sites to extend the record backward by using statistical relationships between co -located, overlapping SNOTEL and Snow Course data. For temperature, precipitation, and April 1 SWE, standard least squares linear regression wa s used to estimate the linear trend (i.e., the slope) and calculate the 2.5% -97.5% confidence interval on the trend to determine statistical significance. A lack of statistical significance was reported if the confidence interval included a trend of zero. Because these estimated confidence intervals assume the observed deviations from the linear trend (i.e., the residuals) are normally distributed, a test to confirm normality was performed. When the residuals were not normally distributed, the Mann -Kendall test, preferred in such cases, was used to assess significance in the trend. Strong autocorrelation in a time series can lead to overly narrow confidence intervals and therefore may lead to an improper conclusion of statistical significance when performing either standard linear regression or the Mann -Kendall test. Therefore, adjustments for autocorrelation were applied when strongly present. Future Projections The future climate projections for Ashland are based on the latest generation of global climate m odels (GCMs) from the Coupled Model Intercomparison Project phase 5 (CMIP5) (Taylor et al., 2012) that were used in the fifth assessment report of the Intergovernmental Panel on Climate Change (IPCC, 2013) . CMIP5 simulations of the 21st century were driven by repres entative concentration pathways (RCPs) that define concentrations of greenhouse gases, aerosols, and chemically active gases leading to set amount of radiative forcing, or extra energy trapped in the earth -atmosphere system, by the year 2100 (van Vuuren et al., 2011) . We consider two of the four RCPs (Figure 21 ): RCP4.5 (“low”) representing moderate efforts to mitigate emissions , and RCP8.5 (“high”) representing a busine ss as usual scenario. In the RCP4.5 scenario, emissions stabilize by mid -century reaching a peak of about 10 gigatonnes of carbon per year (GtC/yr) and then decline in the decades following resulting in a near stabilization of atmospheric carbon dioxide c oncentrations at about 500 ppm by the end of the century . The RCP8.5 scenario represents a continuance of our current pat h of emissions throughout the 21st century that begins to stabilize toward the