Trends in surface 1970-2010 Southern California Maximum Temperatures: Extremes and Heat Waves

Daily maximum temperatures from 1970-2010 were obtained from NCDC for the 28 South Coast Air Basin (SoCAB) COOP sites in the 1970-2005 study of Lebassi et al. (2009). Analyses were carried out on the entire data set, as well as on the 1970-74 and 2006-10 sub-periods, including construction of spatial distributions and time-series trends of both summer-average and annual-maximum values, as well as frequency of two and four consecutive daytime heat-wave events. Spatial patterns of average and extreme values showed three areas consistent with climatological SoCAB flow pat-terns: cold coastal, warm inland low-elevation, and cool further inland mountain top. Difference (2006-10 minus 1970-4) distributions of both average- and extreme-value trends were consistent (but larger than those) from the shorter study of Lebassi et al. (2009), as they showed the expected inland regional-warming and a “reverse-reaction” cooling in low elevation coastal and inland areas open to increasing sea breeze flows. As the warming (and thus the reverse-reaction cooling) trends of extremes were larger than those of the averages, regional-warming thus impacts extremes more than averages. Spatial distributions of heat-wave event-frequencies showed expected maximum at inland low-elevation sites, but no events at both low-elevation coastal and inland high-elevation areas. Regional-warming again induced increases at both elevated-coastal and high-elevation inland areas, but low-elevation areas showed reverse-reaction decreases.