Abstract
Abstract. The Central Netherlands Temperature (CNT) is a monthly daily mean temperature series constructed from homogenized time series from the centre of the Netherlands. The purpose of this series is to offer a homogeneous time series representative of a larger area in order to study large-scale temperature changes. It will also facilitate a comparison with climate models, which resolve similar scales. From 1906 onwards, temperature measurements in the Netherlands have been sufficiently standardized to construct a high-quality series. Long time series have been constructed by merging nearby stations and using the overlap to calibrate the differences. These long time series and a few time series of only a few decades in length have been subjected to a homogeneity analysis in which significant breaks and artificial trends have been corrected. Many of the detected breaks correspond to changes in the observations that are documented in the station metadata. This version of the CNT, to which we attach the version number 1.1, is constructed as the unweighted average of four stations (De Bilt, Winterswijk/Hupsel, Oudenbosch/Gilze-Rijen and Gemert/Volkel) with the stations Eindhoven and Deelen added from 1951 and 1958 onwards, respectively. The global gridded datasets used for detecting and attributing climate change are based on raw observational data. Although some homogeneity adjustments are made, these are not based on knowledge of local circumstances but only on statistical evidence. Despite this handicap, and the fact that these datasets use grid boxes that are far larger then the area associated with that of the Central Netherlands Temperature, the temperature interpolated to the CNT region shows a warming trend that is broadly consistent with the CNT trend in all of these datasets. The actual trends differ from the CNT trend up to 30 %, which highlights the need to base future global gridded temperature datasets on homogenized time series.
Highlights
In the Netherlands, the earliest temperature observations were made at the end of the 17th century
In 1906 a climatological network had become operational in the Netherlands that employed a highly standardized observation practice and a type of Stevenson screens at all stations but one
The exception was the station De Bilt, where this replacement happened on 17 May 1950 and where the Stevenson screen replaced a large thermometer screen, which had a thermograph located at 2.20 m on the peak of the Pagoda’s roof
Summary
In the Netherlands, the earliest temperature observations were made at the end of the 17th century. The first is to construct a set of homogeneous monthly averaged records for daily mean temperature at various locations spread over the Netherlands. These records are either based on long continuous records from the KNMI network or, when these are not available, on combinations of two records from nearby stations to obtain time series as long as possible. Den Helder and Sittard had 9 missing months, Winterswijk had 1 missing month, Hoorn had 6 missing months and Eindhoven missed May and June 1952 These missing data were filled with data from alternative stations with a monthly adjustment to account for any climatological differences (see Tables 1 and 2). This observation made us change the procedure and adjusted both the step and the trend when the metadata indicated that these adjustments were required
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