Understanding Soil Moisture – Precipitation (SM-P) Coupling over India
from a Compound Flood Risk Assessment Perspective
Abstract
Compound event research has gained significant momentum over the past
few years. Traditionally risk assessment studies considered either one
climatic driver or process at a time. However, it is now being
recognised that it is the combination of multiple drivers and their
statistical dependencies that lead to aggravated, non-linear impacts. We
aim to identify hotspots for SM-P coupling over India from 2004 to 2020
using Event Coincidence Analysis (ECA) and an extremal tail dependence
measure. We further characterise how these complex interconnected
interactions can lead to more significant flash floods and landslide
risk. The analysis is done at different temporal scales to pinpoint a
location prone to floods during the year. High precursor coincidence
rates (>60%) were obtained for traditional flash
flood-prone areas over India, indicating the robustness of the approach.
ECA results were compared with the probabilistic extreme value approach,
and a similar pattern was observed in both. The increase in hotspots
from 2004 to 2020 matches the observed increase in flood-prone districts
reported by earlier studies. We also used the trigger coincidence rate
to identify areas where soil moisture anomalies can trigger extreme
precipitation. The seasonal variations in precursor coincidence rates
are observed to be the same as those usually expected due to changing
atmospheric circulation patterns. Our results will complement the
traditional flood risk assessment studies and have implications for
better understanding the dynamic, ever-evolving nature of compound
preconditioned flooding events worldwide.