Abstract:
The Gal Oya River basin is an important
agricultural and water-resource system in eastern Sri
Lanka, but its downstream low-lying areas remain
exposed to rainfall-triggered flooding. Flood generation
in the basin is controlled by seasonal rainfall as well as
atmospheric low-level disturbances, including low-
pressure systems, monsoon lows and troughs, easterly
waves, convergence zones, and organized convective
systems. These processes can modify moisture
convergence and convection and thereby influence
rainfall intensity, duration, and spatial distribution.
This review synthesizes literature on tropical
atmospheric processes, Sri Lankan rainfall systems,
Gal Oya basin hydrology and morphometry, rainfall–
runoff transformation, flood inundation, exposure,
vulnerability, and reservoir operation. A structured
narrative review identified three principal evidence
gaps: limited event-based attribution of Gal Oya
extreme rainfall to atmospheric disturbances;
inadequate integration of atmospheric indicators with
rainfall–runoff and inundation modelling; and limited
basin-specific analysis of downstream hazard, exposure
and vulnerability. The review also shows that satellite
precipitation products should not be used as an
unvalidated substitute for gauge observations during
extreme events because upper-tail rainfall estimates can
contain substantial bias [40]. A review-based analytical
framework is therefore proposed in which disturbance
identification, rainfall attribution, hydrological
response, inundation modelling, and risk assessment
are linked. The framework is intended for future
empirical testing and is not presented as an already
validated predictive model.
