Water risk has been continuously rising due to climate change and ownership disputes of water resources. Dam construction to secure water resources may lead to environmental problems and upstream immersion. On the other hand, rainwater harvesting systems can effectively supply water at a low cost, although economic efficiency of these systems is still debatable. This study evaluates financial support programs to promote installation of rainwater harvesting systems, increasing economic feasibility. Based on a cost–benefit analysis, capacity optimization methods are further suggested. A sensitivity analysis is performed to determine the relative importance among uncertain parameters such as inflation and discount rates. In doing so, priority factors to consider in the design of rainwater harvesting systems are ultimately identified. A net present value, although it is sensitive to the inflation rate, is shown to be more appropriate to estimate the economic efficiency of rainwater harvesting system, compared to the typical cost–benefit ratio. Because the high future value overestimates the economic feasibility of rainwater harvesting systems, proper inflation rates should be applied. All in all, a funding program to promote rainwater harvesting systems significantly increases the benefits. Thus, national financial support policies are recommended to ensure economic feasibility of rainwater harvesting systems.

Factors affecting rainwater resource management for the present and future include population growth, urbanization, and climate change. Rainwater harvesting (RWH) allows multiple urban water-related issues to be mitigated. In this study, a spreadsheet-based daily water balance model was developed to analyze the existing laws and regulations regarding the storage tank size of RWH facilities. Six buildings at different locations were selected for this study. Two are office buildings, two are school buildings, and two are sports buildings. The term “RWH facility evaluation criteria” is collectively used for rainwater supply satisfaction rate, rainwater guarantee rate, and rainwater utilization rate. A green roof can hold the rainwater for some time, reducing the peak flow and runoff volume. The results provide evidence that, among the selected studied buildings, buildings having a combination of a green roof and RWH facility score the highest in terms of RWH facility evaluation criteria, even though the actual tank size is much smaller than the standard tank size. This is the case with the Yesan County Office, in which a green roof connected to a small (66 m³) rainwater storage tank is installed. As a green roof can decrease the runoff volume, the rainwater can be managed efficiently with less pumping energy and only a small storage tank.

The increasing intensity of rainfall resulting from climate change is projected to worsen the inundation of urban areas by floods. As a viable alternative, stormwater harvesting presents an opportunity to enhance water supply reliability while reducing pressure on both water resources and urban stormwater drainage systems. The stored rainwater can be supplied with a radius of one kilometer around the storage facility, so less pumping energy is consumed compared to supplying the stored rainwater far away from the storage facilities. To visually depict the characteristics of the selected storage facility, land cover maps were created using ArcGIS. These maps were created for a circular region with a radius of one kilometer around each studied storage facility. In this study, a daily water balance model was formulated using spreadsheets to assess the potential of harvesting stormwater and rainwater for various pre-existing storage facilities. Five different types of storage facilities were selected for this study. The term “SRWH facility evaluation criteria” as a whole is used for the storm or rain (SR) water supply satisfaction rate, the SR guarantee rate, and the SR utilization rate. The results provide evidence that, for each selected studied storage facility, the SR water guarantee rate can potentially surpass 70% under conditions of low water demand. Moreover, we investigated the potential of the existing storage facilities to work as multifunctional resources, while the original purpose for which each facility was constructed remains un-affected.

Short-term heavy rains caused by global warming could lead to urban flooding as well as damage to both people and property. Although Korea is taking active measures to reduce the impact of flood-related disasters through disaster impact assessments, these assessments mainly consist of qualitative evaluation procedures for urban inundation when designating districts for development projects. The recently developed “inundation determination and detention site size calculation program” has made it possible to review urban inundation hydraulic calculations, even when designating districts for development projects. However, there is still a limit to the hydraulic review and the utilization of Low Impact Development (LID) facilities due to the lack of linkage between the use of such facilities and the inundation determination program. Accordingly, it is necessary to develop a technique to utilize runoff coefficients in applying the LID in the flood determination program. Therefore, in this study, the flood control capacity of stormwater runoff reduction facilities at each LID facility was reviewed and the relationship with runoff coefficient was analyzed.

Stormwater harvesting (SWH) is emerging as a vital adaptive strategy for urban climate resilience. In South Korea, different types of storage facilities have been constructed under different regulations and laws. Each type of storage facility has its own original purpose of construction. Although these facilities have better outcomes, we aim to investigate the potential use of these facilities as additional water resources. In this study, we assess the stormwater harvesting (SWH) potential of different types of already-constructed storage facilities. Five different types of storage facilities and three different cases are considered in the present study. Case 1 excludes SWH volume during the flood and winter seasons, while in Case 2, only winter season SWH volume is excluded. In Case 3, the winter season and combined sewer overflows (CSOs) facilities are excluded. The Rainwater Utilization Facility is considered as a baseline for comparison in the present study. The results show that, in Case 2, the Sewage Storage Facility, Stormwater Runoff Reduction Facility, Nonpoint Pollution Reduction Facility, and Buffer Storage Facility has 53.5, 4, 2.4, and 1.2 times more stormwater average annual usage potential, respectively. The findings suggest that these facilities can be utilized as additional water resources. It should be mentioned that the primary objective for which each facility was constructed will remain unaffected. Nevertheless, forthcoming research should focus on a detailed exploration of the quality of the collected stormwater and the energy required to supply the stormwater for the end usage.

Recently, rainfall runoff models have been introduced for planning a storm sewer network in an urban areas because they can calculate the flood hydrograph as well as peak flow. This would solve the flood problem for the entire watershed. While a rainfall hyetograph is an essential input to a rainfall-runoff model, there is no proper guideline for an urban area on how to obtain a rainfall hyetograph from a temporal distribution of probable rainfall. The purpose of this study is to suggest an appropriate method for temporal distribution of probable rainfall for a storm sewer network. Thus, Huff's quartile method, which is widely used in practice, and the alternating block method (ABM), which is known to be reasonable for planning medium-or small-scale drainage facilities, were compared. The two estimation results were used for the comparison: the probable rainfall amounts by duration; the peak flows from arbitrary watersheds. The results showed that the ABM was more appropriate than the Huff method from three perspectives: reproducibility of actual rainfall phenomena, accuracy of peak flow estimates for small drainage areas in urban regions, and consideration of continuity for the storm sewer network. These results may contribute to enhance planning methods for a storm sewer network in urban areas.