Abstract
Our growing capacity to gather and process continental water coverage
data based on remote sensing has opened new possibilities to understand
the spatial and temporal dynamics of floods. Here we used a 30-year
spanning dataset (Global Surface Water Extent) to elaborate a worldwide
geographical characterization of floods (1-degree grid), and weighted
the relative contribution of seasonal, interannual, and long-term
fluctuations on overall variability, and quantified
precipitation-flooding delays where the seasonal component was dominant.
We explored the distribution of flooding timings in relation to climate,
represented by five main Köppen-Geiger classes, and hydro-topography,
represented by seven classes derived from modeled water table depths.
Our results showed that, globally, the mean extent of floods averaged
0.48% of the land area and was predominantly associated with
hydro-topography (> 2 times higher in cells dominated by
flat bottomlands) and secondarily to climate (less than half in arid
climate cells). Seasonal (interannual) variability decreased (increased)
from boreal to tropical to temperate and arid climates. Predominantly
positive, long-term trends dominated temporal variability in 14% of the
grid cells. We hypothesize that climate change may have a deeper impact
on the temporal variability of floods and its components while land use
and water regulation infrastructure would be more important influencing
their extent. Remote sensing will allow a continuous update of the
geography of floods while the variables used to describe them here may
prove sensitive to distinct dimensions of global change.