How much have California winters warmed over the last century?

Extraordinarily warm 2013-2014 and 2014-2015 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 (T-max) and minimum (T-min) daily temperatures in winter estimated from five gridded data sets. Resulting trends show some consistent features, such as higher trends in T-min than T-max; however, substantial differences exist in the trend magnitudes and spatial patterns due mostly to the nature of spatial interpolation employed in the different data sets. Averaged across California over 1920-2015, T-max trends vary from -0.30 to 1.2 degrees C/century, while T-min trends range from 1.2 to 1.9 degrees C/century. The differences in temperature strongly impact modeled changes in snow water equivalent over the last century (from -5.0 to -7.6km(3)/century).