New ways of correcting certain kinds of systematic errors in historical rainfall intensity data

Abstract

Liquid precipitation measurement and data processing, like any other measurement, is subject of various errors. Efforts have been made to correct errors since the 1600s, but for sub-daily data, adjusting procedures have only recently been created. Our knowledge of precipitation statistics is primarily based on historical data. The concept of historical data covers datasets measured by analogous data recording devices, and those discrete data which were recorded in significantly longer than a one-minute sampling interval. These kinds of data were obtained approximately until the 1990s. Today, a one-minute sampling period is almost exclusively used, and the digital data format makes data processing significantly simpler. Generally, the historical sub-daily data were not corrected, so the measurement errors were inherited into the statistics of rainfall intensity (IDF curves). The article presents the history of rainfall measurement and rainfall intensity measurement, as well as efforts to determine and correct the measurement’s errors. We also present some data adjusting procedures of systematic errors, developed for certain types of rainfall recorders, furthermore a complementary correction of data obtained with a longer sampling period. We also point out the problems arising from the sampling characteristics of the data, estimating its effect. All of these errors result in lower rainfall intensities than the actual rainfall had in the reality in the measurement periods. Inaccurate reference data hinder the accurate understanding of phenomena, as well as the proper verification of surmises related to some details of climate change process. The new procedures are the result of a doctoral research on the issue and provide a suitable tool, even if the application of statistical estimation becomes necessary for the implementation of data correction with respect to some of its elements.