Cost-benefit analysis of decentralized low-impact development (LID) applications in urban areas in the Philippines: a case study of the Canlubang sub-catchment

ABSTRACT Economic assessments of low-impact development (LID) in the Philippines are limited to evaluating primary benefits related to hydrologic performance in micro-scale applications due to limited data and tools for quantifying multiple secondary benefits. This study addressed this through a holistic cost-benefit analysis of rainwater harvesting (RH), green roof (GR), bioretention (BR), and permeable pavement (PP) in residential and industrial settings at the sub-catchment scale. A method to monetize flood damage reduction was developed using a coupled one- and two-dimensional (1D–2D) flood model. Multiple co-benefits, including energy savings, CO2 reduction, air pollutant removal, water savings, and groundwater recharge, were quantified using various benefit transfer methods. Comparisons with gray infrastructure were made using cost, net benefits, benefit-cost ratio, and payback period as decision criteria. The results showed that gray infrastructure offered higher flood damage reduction (residential, 14–91%; industrial, 90–1,407%). However, it was possible to combine LID to achieve better results than gray infrastructure (e.g., residential RH + GR, 24%). Combined alternatives produced higher net benefits (e.g., residential Gray + RH, 17.9 million; industrial Gray + PP, 67.1 million), while individual measures tend to have higher cost-benefit ratios (e.g., residential RH, 1.73; industrial Gray, 1.39). Inclusion of co-benefits significantly improved LID feasibility; hence, proper accounting is needed to increase LID adoption.