6/25/2023 0 Comments Precipitation totals by stateLong-term periods of wet and dry spells can have critical impacts on water supplies. The driest consecutive 5-year interval was 1928–1932, with an annual average of 26.2 inches, and the wettest was 1995–1999, with an annual average of 39.5 inches (Figure 4c). Statewide total annual precipitation has ranged from a low of about 22 inches in 1930 to a high of about 49 inches in 1996, and precipitation can fluctuate greatly between years. Portions of the Coast Range receive more than 100 inches of precipitation annually, while some of the desert areas in the eastern part of the state receive less than 10 inches. Precipitation varies widely across the state and from year to year, with areas west of the Cascades also experiencing a large variation in rainfall amounts across the seasons. The state rarely experiences warm nights due to the moderating effects of the Pacific Ocean in the west and low humidity east of the Cascades (Figure 4b). The number of freezing days has been near or below average since 1995, and the 2000–2004 period had the lowest multiyear value (Figure 4a). In addition to the overall trend of higher average temperatures, the state has experienced below average numbers of very cold nights since 1990 (Figure 3). During the 2005–20–2020 periods, the state experienced the highest number of extremely hot days in the historical record (Figure 2). The year 2015 was the warmest year since records began in 18 was the 3rd warmest (1934 was the 2nd warmest). Temperatures in Oregon have risen about 2.5☏ since the beginning of the 20th century, and temperatures in the 1990s and 2000s were higher than any other historical period (Figure 1). Less warming is expected under a lower emissions future (the coldest end-of-century projections being about 1☏ warmer than the historical average green shading) and more warming under a higher emissions future (the hottest end-of-century projections being about 10☏ warmer than the hottest year in the historical record red shading). Historically unprecedented warming is projected during this century. Observed temperatures are generally within the envelope of model simulations of the historical period (gray shading). Shading indicates the range of annual temperatures from the set of models. Temperatures in Oregon (orange line) have risen about 2.5☏ since the beginning of the 20th century. The shading indicates the range of projected temperature increases from all model simulations and provides a measure of uncertainty in projections. Projected changes for 2006–2100 are from a suite of global climate model simulations for two possible futures: one in which greenhouse gas emissions continue to increase (higher emissions) and another in which greenhouse gas emissions increase at a slower rate (lower emissions). Figure 1: Observed and projected changes (compared to the 1901–1960 average) in near-surface air temperature for Oregon.
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