While industrialization has brought remarkable economic growth and reduced poverty in many nations, it has also given rise to negative environmental consequences. The expansion of cities has resulted in the replacement of natural landscapes and permeable surfaces with impermeable ones such as roads, buildings, housing developments, and parking lots. This transformation has disrupted the hydrology of these areas [1]. The proliferation of impermeable surfaces in numerous countries has reduced the capacity for rainwater to infiltrate the soil, leading to water-related issues including floods ^[2][3][2,3]. According to a study conducted in 2022, Asia, which is home to the world’s largest population, accounting for approximately 61% of the global population (4.7 billion), faces significant challenges in this regard. China is the most populous country globally, with 1.438 billion inhabitants, followed by India (1.380 billion) and Indonesia (273 million) [4]. A lack of green spaces worsens this problem, as areas with high population densities experience more frequent instances of flooding.

Currently, there is growing interest among local governments and non-government organizations in green or nature-based solutions for efficient and sustainable stormwater management to mitigate floods ^[5][6][7][8][5,6,7,8]. Conventional stormwater management systems such as drainage (pipes and conduits) can capture and control stormwater; however, they are less effective at improving water quality. They often focus on flood control and may not adequately address the removal of pollutants and contaminants from runoff [9]. Additionally, some conventional systems can hinder the natural infiltration of stormwater into the ground, reducing groundwater recharge. This can have long-term implications for local aquifers and water resources. Conventional systems may also not be adequately designed to handle the increased frequency and intensity of storms associated with climate change and may become overwhelmed during extreme weather events [9]. Due to these drawbacks, many municipalities and organizations are exploring more sustainable and environmentally friendly stormwater management alternatives, which aim to mimic natural processes and reduce the negative impacts of stormwater runoff. Thus, sustainable stormwater management practices (SSMPs) are introduced to address the limitations of conventional systems, replicating the natural hydrological characteristics of catchment areas, and controlling hydrologic pre-development conditions.

SSMPs involve both stormwater quantity control to mitigate flooding and stormwater quality control to treat and remove pollutants from runoff ^[10][11][10,11]. Considering the altered characteristics of water catchment areas due to urbanization in Asian countries, it is vital to incorporate quantity and quality control parameters into stormwater management planning and design. Several studies have demonstrated the suitability of SSMPs, such as green roofs, rainwater harvesting systems (RHSs), grass swales, rain gardens/bioretention systems, and pervious pavements, for implementation across various sectors, including commercial, industrial, and residential areas [12]. These practices have been investigated extensively to assess their effectiveness in managing the hydrological and hydraulic aspects of urbanization. The aim is to ensure that developing Asian countries have adequate storage capacity to handle runoff and remain protected from overflow events.

In recent times, the utilization of green roof technology has proven to be successful in addressing the issue of managing stormwater. Developed countries’ construction sectors have witnessed significant growth in the adoption of green roofs, as this strategy not only safeguards the local environment but also helps alleviate the detrimental impacts of global warming ^[13][14][13,14]. Meanwhile, RHSs are commonly used as storage tanks to collect and store runoff temporally [15]. The collected runoff can be utilized for various purposes, including toilet flushing, irrigation, and more.

Floods have been a recurring natural phenomenon throughout history, affecting various regions worldwide ^[16][17][18][19,20,21]. In recent times, the risks, frequency, and impacts of floods have been on the rise in Asian coastal megacities ^{[18][19][20][21][22]}[21,22,23,24,25]. In urban coastal areas, various measures are being taken to reduce the risk of flooding. One of these measures involves moving citizens and properties from areas with frequent flooding. For example, the government of Indonesia is in the gradual process of relocating its capital from Jakarta to a safer zone. However, densely populated and economically vibrant countries such as China, Japan, South Korea, Vietnam, the Philippines, Thailand, and Singapore find relocation to be impractical due to its high costs and resistance from individuals and businesses ^[18][21]. Consequently, these cities face significant challenges in managing flood risks while addressing their development needs.

2.2. Sustainable Stormwater Management Practices (SSMPs)

To effectively manage stormwater, the catchment areas are divided into three parts: the roof catchment area, the ground catchment area, and the artificial ground catchment area [12]. These divisions help in planning and designing stormwater management strategies to effectively manage runoff and reduce the risk of flooding in residential areas.

Roof Catchment Area

Green roofs, which involve planting vegetation on rooftops, can help mitigate urban heat islands, improve air quality, conserve energy, and enhance the aesthetics of cities. In developing Asian countries, utilizing roof areas, particularly in high-rise buildings, to implement SSMPs can be a valuable approach to addressing water-related issues. Roofs can account for approximately 50% of the total area in buildings, making them significant potential contributors to stormwater management ^[23][48]. Given the limited availability of land, green roofs have emerged as a viable alternative to convert impermeable surfaces into permeable ones ^[24][49]. Thus, the utilization of roof areas presents a promising opportunity to optimize stormwater management in densely populated and rapidly developing regions. While green roofs offer many environmental and aesthetic benefits, they also come with some drawbacks and challenges ^[25][26][50,51]. For example, green roofs can be expensive to install, primarily due to the need for additional structural support, waterproofing, and planting materials. The initial investment can be a significant barrier for some building owners. Additionally, green roofs require regular maintenance, including watering, pruning, weeding, and pest control. Without proper upkeep, vegetation can become overgrown, and a roof’s integrity may become compromised. Green roofs may also not be suitable for all types of buildings or in all urban environments ^[27][28][52,53]. Factors like roof slope, access, and local climate conditions can limit their applicability. Moreover, these roofs can be heavy, especially when fully saturated with water. Not all buildings are structurally capable of supporting the additional weight, necessitating costly structural modifications. Despite these drawbacks, many of the challenges associated with green roofs can be mitigated with proper planning, design, and ongoing maintenance. Careful consideration of local conditions and expertise in green roof installation can help minimize these disadvantages and maximize the benefits of green roof projects.  Meanwhile, RHSs involve the gathering of water from surfaces that rainfall lands on, which is then stored for future purposes ^[29][70]. There are primarily two distinct approaches to rainwater harvesting: the rooftop method and the surface runoff method. The rooftop method entails collecting rainwater from building rooftops, while the surface runoff method involves capturing rainwater as it flows across various surfaces ^[29][70]. In Malaysia, the performance of an RHS for a community consisting of 200 houses in Renggam, Johor was investigated. The study found that an optimal storage tank size of 160 m3 was suitable for a roof area of 20,000 m2 , providing 60% reliability. Additionally, the proposed model achieved significant water savings of up to 58% ^[30][71]. In a study conducted in Selangor, Malaysia, the water quality of rainwater was assessed to determine its suitability as an alternative source of drinking water. The physicochemical quality parameters of the rainwater met the drinking water standards set by Malaysian authorities, suggesting that it is suitable for consumption ^[31][72]. Other Asian countries may consider this treatment in their efforts to determine the suitability of the harvested rainwater as a drinking source according to their drinking standards. Therefore, regular water quality testing is crucial for ensuring the safety of harvested rainwater, especially for drinking purposes ^[31][72]. Common treatment methods include sedimentation, filtration, UV disinfection, chlorination, and ozone treatment ^[32][73]. The choice of treatment method depends on the specific water quality and local conditions. In summary, harvested rainwater can be a safe and viable source of drinking water in Asian countries, but it requires careful planning, proper infrastructure, regular maintenance, and adherence to water quality standards. When done correctly, rainwater harvesting can help alleviate water scarcity and provide a sustainable source of clean drinking water in many regions. However, it is essential to consider the capacity of rain barrels to handle heavy rainfall and sustain water storage for extended periods ^[32][73]. In the case of rooftop areas, rain barrels may not be able to manage the water load for prolonged durations, posing risks to the roof structure, especially in landed houses, and potentially leading to building collapse. Therefore, careful consideration of the appropriate location for installing rain barrels is crucial. Additionally, many Asian countries experience seasonal variations in rainfall, with heavy monsoon rains followed by long dry spells ^[32][33][73,74]. This makes it difficult to rely solely on RHSs for year-round water supplies, leading to potential shortages during dry periods. The installation of RHSs can be expensive, especially for low-income households in developing Asian countries. The cost of purchasing and installing tanks, gutters, filters, and pumps may be prohibitive for some. However, despite these drawbacks, RHSs remain a valuable and sustainable water management option in many Asian countries ^[32][33][73,74]. To overcome these challenges, it is essential to raise awareness, implement appropriate regulations, provide financial incentives, and invest in research and development to improve the technology and efficiency of rainwater harvesting systems.

2.3. Ground Catchment Area

In urban areas, it is crucial to give careful attention and care to sustainable stormwater management practices (SSMPs) constructed on the ground due to the presence of complex infrastructures. The ground catchment area plays a vital role in allowing runoff storage and natural infiltration into the soil ^[34][80]. Several effective SSMPs that can be implemented on the ground, including grass swales, bioretention systems, rain gardens, permeable pavements, and rain barrels [12]. Implementing grass swales requires careful planning, design, and consideration of local conditions ^[35][81]. In Asian countries, where rapid urbanization and increased development can strain natural resources and exacerbate environmental challenges, the implementation of grass swales can play a vital role in addressing these issues while promoting sustainable and resilient communities. However, grass swales require space for construction, which may not always be available in densely populated urban areas. Land acquisition or repurposing of existing areas may be necessary. Additionally, the effectiveness of grass swales may vary seasonally, with reduced infiltration during dry periods and increased runoff during heavy rains ^[36][82]. Despite these drawbacks, many of these issues can be addressed through proper planning, design, and ongoing management. Grass swales remain a valuable tool in sustainable stormwater management and can be particularly effective when integrated into a broader green infrastructure strategy. The bioretention system could prolong the time it takes for runoff to reach its peak concentration, which in turn promotes enhanced infiltration. This is attributed to the presence of clay in the soil configuration, which facilitates better water absorption and retention within the system ^[37][88]. Rain gardens and bioretention systems operate on similar principles but differ in their design requirements. Although rain gardens are smaller and less complex in design compared to bioretention systems, this practice is still capable of managing small catchment areas of less than two hectares, retaining a substantial amount of runoff, and maintaining the natural condition of the area by reducing the flow rate, peak flow, and total volume of runoff [12]. Selecting appropriate components for rain gardens and bioretention systems is crucial to ensure their long-term performance. Vegetation plays a vital role in enhancing the landscape value of an area ^[10][11][10,11]. Citizens can also economically contribute by using vegetable-based plants for their rain gardens or bioretention systems instead of flower-based plants. Therefore, the implementation of these practices should be encouraged, as they offer numerous benefits beyond stormwater management purposes. While they offer several environmental benefits, these practices require regular maintenance to function effectively ^[38][39][89,90]. This includes removing accumulated sediment, weeds, and debris, as well as replenishing organic mulch. Neglecting maintenance can lead to reduced efficiency and decreased pollutant removal. Additionally, these practices may not perform consistently throughout the year, as their effectiveness can vary with weather conditions, plant growth, and seasonal fluctuations in water flow. However, these practices remain as valuable tools for sustainable stormwater management and improving water quality. Properly designed, installed, and maintained, they can offer a range of environmental benefits while addressing some of the challenges associated with urban runoff and pollution ^[38][39][89,90].

2.4. Artificial Ground Catchment Area

The artificial ground area refers to an area specifically created by humans to manage stormwater. Permeable or porous pavements are designed to facilitate the infiltration of runoff into the ground, resulting in reduced flow and improved water quality in the surrounding area ^[40][99]. For instance, the upper surface of a parking lot can be constructed using porous pavement to store water and mitigate runoff from nearby areas. Other suitable locations for implementing permeable pavements include driveways along roads and sidewalks [12]. Previous studies have demonstrated the effectiveness of porous pavements as a solution for water-related issues. However, it should be noted that porous pavements may not be suitable for heavily loaded or highly trafficked areas ^[41][100]. Therefore, further testing and improvements in porous pavement materials are necessary to broaden their applications in artificial ground catchment areas. Additionally, while the characteristics of porous pavement components have been extensively tested, there is a lack of testing evaluating the performance of porous pavements in terms of water quantity and water quality parameters, specifically in Asian countries. Thus, it is crucial to encourage more experimental or simulation work to assess the suitability of porous pavements for stormwater management in Asian countries. To further promote the implementation of SSMPs in Asian countries, several measures can be taken ^[34][42][43][80,101,102]. One important step is streamlining the permitting processes associated with SSMPs. Simplifying and expediting the approval procedures for implementing these practices can help overcome bureaucratic hurdles and facilitate their widespread adoption. Providing incentives or funding schemes can also incentivize individuals, communities, and organizations to implement SSMPs. Financial support or tax incentives can encourage stakeholders to invest in sustainable stormwater practices and overcome the financial barriers associated with their implementation. Collaboration with local authorities and government agencies is essential. By working together, suitable locations for SSMPs can be identified and integrated into urban planning and development processes. These proactive approaches ensure that stormwater management is considered from the early stages of urban design, leading to more effective and sustainable outcomes ^[34][42][43][80,101,102]. Regular maintenance and operation of SSMPs is crucial to their long-term effectiveness. Trained professionals should be responsible for the ongoing maintenance and monitoring of these practices to ensure their optimal performance. This includes routine inspections, cleaning, and repair work to guarantee their functionality and longevity. By implementing these measures, financial and technical barriers can be overcome, suitable locations for SSMPs can be identified, and the proper operation and maintenance of these practices can be ensured ^[42][44][83,101].