Integrated assessment of the impacts of climate and land-use changes on future flooding and effective adaptation in the Gin River Basin, Sri Lanka

Abstract

Study region: Gin River Basin, Sri Lanka. Study focus: The individual and combined effects of climate and land-use changes on flood flow and inundation in the Gin River basin, Sri Lanka, were assessed. Downscaled, bias-corrected future precipitation projected by an ensemble of general circulation models (GCMs) under the Representative Concentration Pathway (RCP) 4.5 emissions scenario was input into a flood model developed using the Rainfall Runoff Inundation (RRI) model. Possible flood mitigation measures were identified based on flood simulations through the integrated assessment incorporating future climate and land-use projections. New hydrological insights for the region: The basin is projected to receive increased rainfall during the southwest monsoon (9.7 %) and second inter-monsoon (15.7 %) seasons, excluding March and April, in the future. Human settlements will expand in the downstream areas of the basin, while a significant share of agricultural land (27 %) in the basin will be converted into shrublands by 2050. High flows are predicted to increase by 16 % and 4 % at the upstream and downstream gauging stations, respectively, while mean river flow is expected to decrease by 25 % (upstream) and 34 % (downstream). In addition, a 3.5 % increase in annual maximum inundation extent is projected. However, the total inundation extent in the basin can be reduced by 1.3 % by regulating land-use changes, particularly the conversion of agricultural land into riparian forests.

Keywords

• Floods
• Gin river
• Climate change
• Land-use
• Riparian forests
• Rainfall Runoff Inundation (RRI) model