The oldest instrumental hydrological and meteorological records in Prague as a basis for the resimulation of the flood of February 1784

In 2025, Czech hydrology celebrates several significant anniversaries. In 1775, the uninterrupted temperature series in the Klementinum Observatory in Prague began, in 1825 daily observations of water levels in Prague began, and in 1875 the hydrological service in Prague was established (Elleder, 2019). As far as 1775 is concerned, this is more about meteorological observations, but even here we find references to floods and droughts in the observation diaries, and the earliest records of rainfall and snow heights. Here, we focus on the first decade of observations (1775– 1785), when the extreme flood of February 1784 occurred. In 1781, the first water gauge in Prague was established by the Klementinum Observatory when it was incorporated into the Societas Meteorologica Palatina (SMP). However, these were only occasional observations of water levels. The floods of 1782, 1783 and 1784 were partially documented with the help of this water gauge. For the time of the flood (February 1784) we have incomplete records only for the beginning and end of the flood. The course of the water levels is still known relatively accurately in Prague, Beroun, Dresden and then Magdeburg.  The hydrograph of this extreme flood in Prague was reconstructed from indirect evidence of water levels (Elleder, 2010). The rate of water rise was enormous, up to 30 cm per hour. Using the Aqualog system, standardly used for hydrological forecasting, we have now attempted a hydrological re-simulation of this flood in the context of the entire Vltava basin in front of Prague. This means the scenarios generated only from measurements of temperature, air pressure and partly precipitation in Prague, or in relatively near stations Regensburg, Budapest, Zagan, Erfurt and Mannheim. Problems arose in obtaining rain and snowfall data due to uncertainties regarding the recording of precipitation in Prague. To better understand how precipitation is recorded, we attempted to consider measurements at other SMP observatory sites.   We documented the conditions of the severe winter that preceded the flood, including the likely ice thickness, water value of the snow, and partial rainfall. Using re-simulations with the Aqualogic modelling system, we obtained an approximate agreement of the water level courses in Beroun and Prague in terms of time, culmination and flood volume. The steep rise in levels could not be explained.  The flood in its entire European context is gradually being included in the Maps of Extreme Floods - MEF (Elleder and Šírová, 2023). We started with a reanalysis of the 1784 flood by showing reconstructions of major European floods, where documentary data are collected in advance in the MEF 2020 application. To date it is the most significant winter flood in Prague.

References:

Elleder, L., (2010) Reconstruction of the 1784 flood hydrograph for the Vltava River in Prague, Czech Republic. Global and Planetary Change 70, 117–124.

Elleder, L. 2019. A. R. Harlacher and his Role in founding of Czech Hydrological Service in Prague in 1875, https://meetingorganizer.copernicus.org/EGU2019/EGU2019-7860.pdf.

Elleder, L. Šírová, J. (2023) MEF application- the extreme floods are already in maps!

        https://meetingorganizer.copernicus.org/EGU23/EGU23-3160.html.