Atmospheric Low-Level Disturbances, Rainfall, and Downstream Flood Risk in the Gal Oya River Basin, Sri Lanka: A Review

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.