Climate and Energy Action Plan (CEAP)

CLIMATE TRENDS & PRO JECTIONS | CITY OF ASHLAND, OREGON | FINAL REPORT | 19 Total Precipitation Historical Trends Total water year (October -September) precipitation in Ashland decreased at a rate of 0.9 inches per c entury over the period 1893 -2014 , but the trend is not significantly different from there being no trend at all (see Figure 11). Likewise, there we re no significant trend s in precipitation for any season in Ashland (Table 3). Like Ashland, water year precipitation at the majority of stations in the PNW and averaged over the PNW exhibits considerable variability from year to year and decade to decade with no significant trends from 1901 to 2012 (Abatzoglou et al., 2014) . Unlike for temperature trends, increasing greenhouse gases did not contribute significantly to t he observed PNW precipitation trends in any season, suggesting that natural variability is larger than any climate change signal over this period (Abatzoglou et al., 2014) . Figure 11. Total water year precipitation in Ashland exhibits large variability and a decreasing trend that is not significantly different from zero during the period 1893 -2014 . Future Projections The rang e of future changes in total precipitation amount in Ashland is -2.4 to +2.4 inches for the 2050s and - 2.7 to +3 .9 inches for the 2080s across all models and both emissions scenarios (Table 2). The multi -model mean projects an inc rease of about 0.4 inches by the 2080s under the high emissions scenario compared to the histori c baseline (1950 -2005) ( see Figure 12). In other words, climate models do not agree on whether annual total precipitation will increase or decrease. Seasonally, precipitation is projected to increase during the winter months and remain about the same or decrease at other times of the year. However, in every season, some climate models project increases and others project decreases (Figure 12). Natural variability will continue to play a dominant role in future precipitation through the end of the 21st century. From a global perspective, changes in precipitation in response to warming will manifest as a larger contr ast between wet and dry regions and seasons, although there may be regional exceptions. In the near term, precipitation changes will largely reflect natural internal variability. By the end of the 21st century under the highest emissions scenario (RCP8.5), high latitudes and the equatorial Pacific Ocean are likely to experience an increase in annual mean precipitation. Mean precipitation is likely to decrease in many dry regions in the subtropics and mid -latitudes and increase in many mid -latitude wet regio ns (IPCC 2013). Where exactly that 1900 1920 1940 1960 1980 200010 15 20 25 30Ashland T otal W ater Y ear Precipitation Water Y earInchestrend: −0.9 in/centur y