Extreme hydrometeorological events, a challenge for gravimetric and
seismology networks
Abstract
Extreme events will become more common due to global change, requiring
enhanced monitoring and pushing conventional observation networks to
their limits. This encourages us to combine all the possible sources of
information to obtain a complete picture of extreme events and their
evolution. This commentary builds on an example of the July 2021
catastrophic floods that hit northwest Europe, for which the use of
seismometer and gravimeter captures complementary data and brings a new
understanding of the event and its dynamics. A sudden increase in
seismic noise coincides with the testimony reporting on a “tsunami”
downstream of the geophysical station. Concurrently, the gravimeter
showed increasing saturation of the weathered zone, showing less and
less water accumulation and increasing runoff. When rain re-intensified
after a 3-hour break, the subsoil’s saturation state induced an
accelerated runoff increase, as revealed by the river flow, in a much
stronger way than during the rainy episodes just before. We show that
the gravimeter detected the saturation of the catchment subsoil and soil
in real-time. When the rain re-intensified, this saturation resulted in
a sudden, devastating and deadly flood. Our study opens up the
possibility of integrating real-time gravity in early warning systems
for such events.