Intercomparison of Measurements at Climate Reference Stations in Germany

To ensure consistent time series of climate observations, the German Meteorological Service (DWD) operates out parallel measurements (e.g. wind and precipitation measurements) at climate reference stations. Parallel measurements of subsequent generations of operational measurement systems are carried out over several years at selected ten locations with different environmental conditions in order to evaluate the quality of the data obtained, to analyse systematic differences between the instrument types and to ensure the homogeneity of the data series.

A key feature of climate reference observations is that they are monitored consistently over long periods of time to ensure a high degree of comparability of observations. Inconsistent data series are of limited use in climate research. In order to assess the consistency of climate observations, these time series must be described in detail using metadata and, in particular, by reliably specifying measurement uncertainties. The overall objective is to ensure the consistency of measurements, especially before and after sensor changes, and to develop the necessary automated procedures to detect breaks caused by instrument changes and to homogenise measurement series. This will ensure that the data remain consistent over long periods of time.

Precipitation measurements are affected by several factors that can lead to systematic underestimations. One of these factors is evaporation. This error can be significant, especially for automatic precipitation gauges equipped with a heating system. However, the potentially largest error is triggered by wind. The shape of the funnel influences the wind field around the gauge and small turbulence can occur which can blow snow and small raindrops in particular over the gauge, leading to an underestimation of precipitation.  To minimise this error, primary gauging stations are equipped with a wind shield, while secondary gauging stations are not.

These differences can vary from gauge to gauge, leading to inhomogeneities in long series of measurements.  In order to analyse and quantify these and other influences, the German Weather Service has established climate reference stations at ten locations with different natural conditions.