PluvioReader: A software for digitizing weekly siphoning-type pluviograph strip charts

Abstract

Long, continuously-gaged precipitation records are needed for characterizing extreme rainfall events over sub-daily durations, as well as detecting potential historical effects of climate change. However, most such records predating the 1980s are in the form of paper strip charts (pluviograms), from which it is notoriously difficult to extract extreme precipitation depths for short durations (from a few minutes to a few hours). We propose a highly accurate method for digitizing weekly strip charts from float and siphon pluviographs and obtaining continuous rainfall data from them. The method's main inputs are the digital image of a strip chart and its recording time window (typically one day or one week). With this data, the software sequentially performs four processes: (1) it identifies the ink-traced line in the digital image, (2) it joins any separated segments of the line and removes elements that are not part of it, (3) it defines the line in Cartesian coordinates, and (4) it converts the defined line into precipitation values. The method has been implemented in the PluvioReader software, with a friendly and intuitive user interface that allows for easy handling of inputs and outputs, and includes basic image editing tools. The PluvioReader software has been tested on more than 800 weekly strip charts from several stations in Chile, successfully extracting precipitation series down to a 5-min resolution, even from complex pluviograms with multiple drainage events and steep lines.

Publication Title

Computers and Geosciences

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