Abstract:
This study, for the first time, investigates the physical association between Predecessor
Rain Events (PREs) and peak runoff generation in seven catchments over the
Upper Mahanadi River basin (UMRB), India. A statistical–dynamical framework is
developed to assess the compounding impact of PREs (as preconditioned events) versus
riverine floods during both retrospective and projected climate. Based on models'
fidelity to capture historical climatology, we select four out of nine Global Climate
Models (GCMs) during historical (1980–2005), and the three projected time windows,
that is, near future (2010–2039), mid-century (2040–2069), and the far future
(2070–2099) planning horizons with RCP8.5 emission scenario. We assess changes
in compound flood hazards in historical versus projected periods using a newly proposed
Bivariate Hazard Ratio (BHR) index, which represents the ratio between bivariate
return periods during the projected versus the historical time windows. Assessing
bivariate return periods (characterized by ‘AND’ operator) of rainfall-driven compound
floods shows decreased flood hazard in the mid-century and far-future planning
horizons. Accounting ranges of uncertainty from climate model simulations and
the propagation of uncertainty across the numerical model chain, overall we show
considering PRE as the covariate, floods in larger catchments show an increase in
compound flood hazard in the projected period.
