The Karlsruhe temperature time series since 1779

This paper presents the long-term Karlsruhe temperature series re-digitized and reconstructed from handwritten manuscripts from 1779 to 1875 archived in various libraries. Despite great efforts, data from some periods remained missing in the manuscript departments so that the main Karlsruhe series remained partially fragmented. Combined with historic climate records available in the archive of German Weather Service (DWD), the entire series until 2008, when the official Karlsruhe station was relocated to Rheinstetten, is one of the longest climate series available for Germany. The series includes various observational parameters on a daily or even sub-daily basis converted into SI units or contemporary units.The focus of this paper is on the temperature series and presents some first statistical analyses to demonstrate the additional benefit of possessing unique long-term instrumental climate data on a sub-daily basis. The entire temperature series was homogenized with respect to consistent observation times and to a location on the city's periphery. It is shown that the width of the distribution function quantified from constructed daily maximum and minimum temperature has substantially broadened in the summer months, but not during winter or the entire year. The number of summer and hot days has substantially increased in the last 30–50 years, while the number of frost and ice days has decreased. Summer or hot days as well as heat waves were very rare before 1920, being unrepresentative of a period mainly unaffected by climate change. Singularities of the climate system, such as the (cold) Schafskälte in June or the (warm) Hundstage in July/August, are clearly shown in most periods. The (cold) Ice Saints in May, however, have a high frequency only in the coldest period between 1870 and 1960; they are hardly detectable in most of the preceding years. Temperature statistics show that the severity of late spring frosts has gradually increased during the entire record mainly as a result of later frost occurrences.