Analysis of California surface temperature trends based on observations

Analysis of California surface temperature based on observations has been conducted using United States Historical Climatology Network (USHCN) stations and Cooperative Weather (COOP) stations throughout California to understand spatial and temporal changes in temperature. Monthly maximum and minimum temperatures (Tmax and Tmin) were used to calculate and analyze annual and seasonal trends over the last 86 years via statistical analyses. For annual trends, Tmin is warming faster than Tmax for both 1918--2006 and 1950--2006 time periods. Since 1970, both Tmax and Tmin, however, have increased at the same rate. For seasonal trends, interestingly, by far the largest warming trends are found during spring (March--May) in both Tmax and Tmin, particularly in Southern California since 1970. While Tmin reveals a strong coherent temperature variation statewide in both annual and seasonal temperatures, Tmax shows spatial and temporal variations in finer scales. Particularly in Southern California during winter and summer, cooling and warming trends are leveled in Tmax. These regional temperature changes must be caused by different forcing mechanisms.