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Urban flooding has increased in response to impervious surface intensification, the loss of green areas, and high-intensity rainfall associated with climate change. Sustainable urban drainage systems (SUDS) are an appealing option for stormwater management; however, their hydraulic control capabilities have received little attention. We developed a comparative model-based approach with 24 scenarios to contrast the hydrologic and hydraulic response of a highly discretized (HD) 1D model and a coupled 1D–2D model, considering the impact of rainwater harvesting systems and tree pits. An additional scenario was modeled including attenuation storage tanks, green roofs, and pervious pavements. A heavily urbanized flood-prone catchment with severe land-use constraints in Bogotá, Colombia, was selected for analysis. The findings revealed that SUDS can contribute to reducing the number of flooded junctions, overloaded conduits' length, overloading time, nodal inundation depth, and waterlogging extent. Furthermore, the HD 1D model can reproduce the coupled 1D–2D model results in terms of hydrologic response and some hydraulic control indicators. Further research is needed for an accurate description of the internal hydraulic mechanisms of SUDS interacting with overland flow. The key findings of this study provide model-based evidence to support urban stormwater management decision-making in data-scarce environments. HIGHLIGHTS 24 scenarios contrasting SUDS performance using a HD 1D and a coupled 1D–2D model.; Discussion on data requirements, limitations, and hydrologic–hydraulic response.; HD 1D models can reproduce the hydrologic response of 1D–2D models.; HD 1D models can partially reproduce the hydraulic 1D–2D model results.; SUDS provide hydraulic control in heavily urbanized areas.;

Study region: Karnali-Mohana river basin, Western Nepal. Study focus: This study aims to project future climate and assess impacts of climate change (CC) on water availability in the Karnali-Mohana (KarMo) basin. Bias-corrected future climate was projected based on ensembles of multiple models selected from a set of 19 regional climate models (RCMs). The impacts on water availability were then assessed by forcing a well calibrated and validated hydrological model with projected future precipitation (P) and temperature (T) for various climatic scenarios. New hydrological insights for this region: Results showed that future T is projected to increase spatio-temporally with higher rate for the mountain stations in the winter season; whereas future P has no distinct spatio-temporal trend but increase in dry season precipitation for future periods. The projected changes in P, T and evapotranspiration are expected to alter average annual flow at the outlets of the KarMo and its sub-basins, albeit with varying rate. The simulated results showed higher impacts in water availabilty at higher altitudes, thus indicating higher vulnerability of northern mountainous region to CC than the southern flatlands. Being the first ever study of such nature in the study area, these results will be useful for planning and development of climate-resilient water development projects in the region.

Study region: Karnali-Mohana (KarMo) river basin, Western Nepal. Study focus: This study has developed a hydrological model using multi-site calibration approach for a large basin, the Karnali-Mohana (KarMo) in Western Nepal, which has a lot of potential for water resources development and contribute to the national prosperity. It further applies the model to characterize hydrology and water resources availability across spatio-temporal scales to enhance understanding on water availability and potential uses. The newly developed hydrological model in Soil and Water Assessment Tool (SWAT) is capable of reproducing the hydrological pattern, the average flows, and the flow duration curve at the outlet of the basin and five major sub-basins. New hydrological insights for this region: The model simulated results showed that about 34 % of average annual precipitation in the KarMo basin is lost as evapotranspiration, but with a large spatio-temporal heterogeneity. The Hills and Tarai are relatively wetter than the Mountains. The average annual flow volume at the basin outlet is estimated as 46,250 million-cubic-meters (MCM). The hydrological characterization made in this study are further used for climate change impact assessment (Part-B in the same journal), environmental flows assessment and evaluating trade-offs among various water development pathways, which are published elsewhere. This model, therefore, has potential to contribute for strategic planning and sustainable management of water resources to fuel the country’s prosperity.

Integrated Water Resources Management (IWRM) still stands today as one of the most influential governance models in the water sector. Whereas previous analyses of IWRM have focused on the effectiveness of the institutional models it embodies and on policy implementation gaps, we examine the meanings that IWRM discourses have given to water management issues and how these meanings have in turn supported certain policy choices, institutions and practices. We use discourse analysis to study IWRM discourses in Nepal, where IWRM was introduced as the guiding policy principle for water management more than a decade ago, but not yet operationalised. We argue that IWRM discourses have operated a discursive closure in policy debates, thereby limiting the range of policy and institutional choices perceived as politically possible. In particular, we found that the promotion of IWRM as an institutional holy grail has obscured critical issues of social (in)justice related to water resources development by promoting an apolitical and techno-managerial vision of water development, largely centralised and relying on expert knowledge. We defend the need to move away from institutional panaceas and towards deliberative processes that allow alternative voices, discourses and knowledge.

The term "environmental flows" refers to a combination of features, including quantity, quality, and timing of water flows required to sustainably maintain a river's health, balancing both ecological and societal needs. Incorporating basic human livelihood and sociocultural aspects in environmental flow assessments alongside ecological concerns provides a more holistic perspective on water flow management. Here, we provide an assessment that complements an ecosystem functioning lens by focusing solely on quantifying the flows associated with livelihood activities and spiritual water requirements of local riparian communities in the Karnali basin in Western Nepal. This assessment is based on the first social survey related to environmental flows conducted in the Karnali basin. We collected data using mixed methods, including social surveys, key informant interviews, and focus group discussions, across six locations in the Karnali basin that provide us with a rich and dynamic perspective on the relationship between rivers and their surrounding communities, and the challenges faced by those communities. Among the subsistence and spiritual requirements of local communities are uses for activities that include drinking, small-scale irrigation, domestic needs, fishing, and ceremonial usage. All communities we visited most strongly associated the following activities with water flow variation: small-scale irrigation, fishing, ceremonial usage, domestic needs, and tourism. The water flows required for these key activities were quantified, and results from the six sites are presented in the form of a qualitative scale of minimum water levels (ranging across poor, acceptable, and ideal) required to meet vital local needs. The minimum acceptable water flow requirement to satisfy social criteria is just > 20% of the mean annual runoff at the visited locations. These requirements are particularly vital to consider, given ongoing efforts to tap the vast hydropower potential in Nepal through construction of major storage projects. Such projects would change the flow regime of affected rivers and potentially raise concerns that existing demands might be compromised.

The Himalayas are highly susceptible to the impacts of climate change, as it consequently increases the vulnerability of downstream communities, livelihoods and ecosystems. Western Nepal currently holds significant potential as multiple opportunities for water development within the country are underway. However, it is also identified as one of the most vulnerable regions to climate change, with both an increase in the occurrence of natural disasters and exacerbated severity and impacts levels. Regional climate model (RCM) projections indicate warmer weather with higher variability in rainfall for this region. This paper combines bio-physical and social approaches to further study and understand the current climate shocks and responses present in Western Nepal. Data was collected from 3660 households across 122 primary sampling units across the Karnali, Mahakali and Mohana River basins along with focus group discussions, which provided a rich understanding of the currently perceived climatic shocks and related events. Further analysis of climatology was carried out through nine indices of precipitation and temperature that were found to be relevant to the discussed climate shocks. Results show that 79% of households reported experiencing at least one type of climate shock in the five-year period and the most common occurrence was droughts, which is also supported by the climate data. Disaggregated results show that perception varies with the region and among the basins. Analysis of climatic trends further show that irregular weather is most common in the hill region, although average reported frequency of irregular weather is higher in the mountain. Further analysis into the severity and response to climatic shocks suggest an imminent need for better adaptation strategies. This study’s results show that a vast majority of respondents lack proper access to knowledge and that successful adaptation strategies must be adapted to specific regions to meet communities’ local needs.