Flooding Threshold Rainfall Events in Bermuda

Recently, much media attention has been drawn to the relatively frequent ‘nuisance’ flooding of urban low-lying and poor drainage areas in Bermuda. This flooding results in traffic disruptions and loss of business, with only minor property damage. More significant flooding with property inundations is relatively rare. Efforts were made to reduce the incidence of flooding in low-lying areas of Pembroke Parish through the construction of a canal in the 1800s. However, recent urbanisation and inadequate maintenance have reduced both its drainage capacity and efficiency. There is currently no formal warning system in place for flooding in Bermuda. The results of this study may serve as the context for the development of such a system.

Recent heavy rain and flooding in January 2017 further motivates an examination of the rainfall record for trends and variability in daily rainfall accumulations. A conservative catalogue of flood reports can be constructed from anecdotal reports of flooding for the last decade. The flood catalogue events are related to daily rainfall amounts to develop a threshold daily rainfall for flood events, determined to be on average 39.3mm of rain. This threshold was used as a basis for examination of the historical record of daily rainfall for the period 1949–2016, in order to assess return frequencies of flood-inducing rainfall events. A return period of approximately 2 months was calculated for the threshold daily rainfall accumulation. Although there are increasing trends apparent in the daily rainfall accumulations and counts of days on which rain was recorded (‘rain days’) since 1949, they are not statistically significant.

Johnston, M. C., Guishard, M. P., PeƱate, I. and Currie, I. D. (2018), Flooding threshold rainfall events in Bermuda. Weather. doi:10.1002/wea.3096