How much have California winters warmed over the last century

Extraordinarily warm 2013-14 and 2014-15 winter temperatures in California accompanied by drought conditions contributed to low snow accumulations and stressed water resources, giving rise to the question: how much has California's climate warmed over the last century? We examine long-term trends in maximum (Tmax) and minimum (Tmin) daily temperatures in winter estimated from five gridded datasets. Resulting trends show some consistent features, such as higher trends in Tmin than Tmax, however substantial differences exist in the trend magnitudes and spatial patterns due mostly to the nature of spatial interpolation employed in the different datasets. Averaged across California over 1920-2015, Tmax trends vary from -0.30 to 1.2 °C/century while Tmin trends range from 1.2 to 1.9 °C/century. The differences in temperature strongly impact modeled changes in Snow Water Equivalent (SWE) over the last century (from -5.0 to -7.6 km3/century).