Should seasonal rainfall forecasts be used for flood preparedness?

In light of strong encouragement for disaster managers
to use climate services for flood preparation, we question
whether seasonal rainfall forecasts should indeed be
used as indicators of the likelihood of flooding. Here, we investigate
the primary indicators of flooding at the seasonal
timescale across sub-Saharan Africa. Given the sparsity of
hydrological observations, we input bias-corrected reanalysis
rainfall into the Global Flood Awareness System to identify
seasonal indicators of floodiness. Results demonstrate
that in some regions of western, central, and eastern Africa
with typically wet climates, even a perfect tercile forecast
of seasonal total rainfall would provide little to no indication
of the seasonal likelihood of flooding. The number of
extreme events within a season shows the highest correlations
with floodiness consistently across regions. Otherwise,
results vary across climate regimes: floodiness in arid regions
in southern and eastern Africa shows the strongest correlations
with seasonal average soil moisture and seasonal total
rainfall. Floodiness in wetter climates of western and central
Africa and Madagascar shows the strongest relationship with
measures of the intensity of seasonal rainfall. Measures of
rainfall patterns, such as the length of dry spells, are least related
to seasonal floodiness across the continent. Ultimately,
identifying the drivers of seasonal flooding can be used to
improve forecast information for flood preparedness and to
avoid misleading decision-makers.