Peri-urban Catchment Research Articles

Peri-Urban Floodscapes: Identifying and Analyzing Flood Risk Areas in North Bhubaneswar in Eastern India

Peri-urban catchment areas are increasingly susceptible to floods due to rapid land use transformations and unplanned urban expansion. This study comprehensively examines flood vulnerability in the rapidly developing peri-urban areas of North Bhubaneswar, focusing on significant changes in Land Use/Land Cover (LULC) and hydrological dynamics from 2004 to 2024, utilizing Geographic Information System (GIS) tools. The analysis reveals substantial shifts in land use patterns, with the urban footprint expanding by 71.8%, cropland decreasing by 21.7%, and forest areas by 13.6%. These changes have led to increased impervious surfaces, resulting in higher surface runoff and decreased groundwater recharge, thereby exacerbating flood risks in the region. The GRID-based vulnerability analysis classifies 90 villages within the catchment area based on their vulnerability levels, identifying 20 villages as high-risk areas requiring urgent attention, 44 villages as medium vulnerable, and 26 villages as low vulnerable. These classifications are based on factors such as proximity to drainage networks, slope, geomorphology, and LULC characteristics, with areas near drainage channels and low-lying regions being prone to flooding. The analysis integrates multiple factors to provide a comprehensive assessment of flood risk, highlighting the need for sustainable land use planning, conservation of vegetated areas, and the implementation of advanced flood prevention strategies in the peri-urban areas. Extending this research to other fringe regions could offer further valuable insights, guiding flood prevention and sustainable development strategies for areas undergoing significant land use transformations to effectively mitigate future flood risks.

Water quality benefits of implementing Green and Blue Infrastructure in a peri-urban catchment – Case study of a Brazilian metropolis

This paper investigates the effectiveness of Green and Blue Infrastructure (GBI) in managing non-point source pollution in the 120 km2 catchment of the Vargem das Flores reservoir, which supplies water to 600,000 inhabitants in the Belo Horizonte metropolitan area, Brazil's third-largest metropolis. A calibrated water quality model within the Storm Water Management Model (SWMM) was used to simulate total suspended solids (TSS) and nutrients loads under different future land use scenarios. The first scenario reflects maximum urban development according to current legislation. An alternative scenario was proposed considering the protection of forest remnants and the adoption of the most cost-effective GBI techniques in newly developed areas. Results indicated a substantial contribution of diffuse pollution to the reservoir's water quality degradation, mainly due to TSS loads transported from the most urbanized subcatchments. The application of bioretention cells to treat 12.6 km2 new impervious areas effectively mitigated diffuse pollution, removing 52.1% of TSS, 19.5% of total phosphorus (TP), and 17.1% of chemical oxygen demand (COD) loads flowing into the reservoir. The GBI implementation would maintain pollutant loads similar to current levels despite the increased urbanization.

Communities’ Perceptions and Coping Strategies to Flood Hazard in a Peri-Urban Catchment: The Case Study of the Zio River Basin, Togo, West Africa

Climate and land use changes have exacerbated the frequency and intensity of floods in West Africa. In Togo, the communities of the Zio river sub-basin are regularly affected by flood hazard with severe socio-economic consequences. The main objective of this article is to contribute to the improvement of the resilience of these populations through a better understanding of their perceptions and coping strategies to flood hazards. To achieve this goal, a mixed method consisting of household surveys, focus groups and direct observation is used. In addition, the data collected at the household level focused on the perceptions of the flood (origin and cause), the socio-economic impacts as well as the coping strategies. The results indicate that more than 80% of the households are affected by floods and the main negative consequences are the destruction of houses (40.8%), and interruption of socio-economic activities (58.4%). In addition, the efforts to cope with the severe impacts of floods include embankment (71.6%), storage on occasional shelves (52.3%), digging ditches (26.6% and the construction of cement houses with fairly raised foundations (13.1%). This study shows that is important to integrate indigenous knowledge and local population’s opinions in the flood risk management plans in order to increase their resilience.

Comparing the Fate and Transport of MS2 Bacteriophage and Sodium Fluorescein in a Karstic Chalk Aquifer.

Groundwater flow and contaminant migration tracing is a vital method of identifying and characterising pollutant source-pathway-receptor linkages in karst aquifers. Bacteriophages are an attractive alternative tracer to non-reactive fluorescent dye tracers, as high titres (>1012 pfu mL-1) can be safely released into the aquifer, offering improved tracer detectability. However, the interpretation of bacteriophage tracer breakthrough curves is complicated as their fate and transport are impacted by aquifer physicochemical conditions. A comparative tracer migration experiment was conducted in a peri-urban catchment in southeast England to characterise the behaviour of MS2 bacteriophage relative to sodium fluorescein dye in a karstic chalk aquifer. Tracers were released into a stream sink and detected at two abstraction boreholes located 3 km and 10 km away. At both sites, the loss of MS2 phage greatly exceeded that of the solute tracer. In contrast, the qualitative shape of the dye and phage breakthrough curves were visually very similar, suggesting that the bacteriophage arriving at each site was governed by comparable transport parameters to the non-reactive dye tracer. The colloid filtration theory was applied to explain the apparent contradiction of comparable tracer breakthrough patterns despite massive phage losses in the subsurface. One-dimensional transport models were also fitted to each breakthrough curve to facilitate a quantitative comparison of the transport parameter values. The model results suggest that the bacteriophage migrates through the conduit system slightly faster than the fluorescent dye, but that the former is significantly less dispersed. These results suggest that whilst the bacteriophage tracer cannot be used to predict receptor concentrations from transport via karstic flow paths, it can provide estimates for groundwater flow and solute contaminant transit times. This study also provides insight into the attenuation and transport of pathogenic viruses in karstic chalk aquifers.

Assessing spatial scales in hydrological effectiveness and economic costs of nature-based solutions within a scale-invariance framework

This study proposed a scale-invariance framework within the fractal and Universal Multifractal (UM) framework to assess hydrological performances and economic dimensions of nature-based solutions (NBS) across various spatial scales. Firstly, a series of NBS scenarios are created by implementing NBS heterogeneously over Guyancourt city (a peri-urban catchment located in the Southwest of Paris). Then, the spatial heterogeneity and the implementation levels of NBS in the NBS scenarios are quantified by a scale-invariance indicator (fractal dimension; DF) across various spatial scales. The X-band radar rainfall data with high space-time resolution was obtained from École des Ponts ParisTech, which is used as the rainfall forcing for numerical modelling experiments. Then, the hydrological responses of the NBS scenarios are simulated by using the fully distributed and physically-based hydrological model (Multi-Hydro) under the selected spatially variable rainfall event. The renormalised maximum probable singularity indicator (RI) is developed based on the UM framework, and it is employed to quantify the hydrological effectiveness in terms of efficiency in runoff reduction of the NBS scenarios. The economic indicator is represented by the life cycle costs (LCC), which are used to estimate the economic costs of NBS scenarios. Finally, the economic dimensions of NBS across various spatial scales are quantified by integrating DF and the LCC of NBS scenarios. The results show that the permeable pavement scenarios 3 and 4 perform better than the other NBS scenarios in mitigating overland flow. The assessment of the economic dimensions of NBS suggests that a higher implementation level of NBS measures in the small-scale range is necessary. The economic dimensions of NBS at the large-scale range vary between 225 m2 and 600 m2. Overall, this study will potentially provide valuable strategies for better managing stormwater runoff in urban catchments and support the decision-making processes of implementing NBS on multiple spatial scales.

The impact of stormwater management strategies on the flow regime of a peri-urban catchment facing urbanisation and climate change: a distributed modelling study in Lyon, France

ABSTRACT The relative impact of urbanisation (urban sprawl), climate change (rainfall and evapotranspiration) and stormwater disconnection strategies (implementation of green infrastructure (GI)) on a peri-urban stream in the western suburbs of Lyon, France, was investigated using a distributed, physically based model (J2000P). Results showed that ambitious catchment-scale implementation of GI has the potential to mitigate some hydrological effects of urbanisation, especially a drastic reduction of combined sewer overflows. However, GI did not have a large impact on the stream flow regime, especially in the context of climate change, as the stream is dominated by non-urban contributions. Spatially distributed models have the capacity to inform river managers about the extent of implementation of GI needed to achieve given management goals and highlight some limitations of disconnection strategies. Indeed, while GI improved the resilience of sewer networks to global change, it was not sufficient to compensate for the effects of climate change on streamflow.

Assessing soil erosion risk in a peri-urban catchment of the Lake Victoria basin.

Soil erosion and sedimentation contribute to deteriorating water quality, adverse alterations in basin hydrology and overall ecosystem biogeochemistry. Thus, understanding soil erosion patterns in catchments is critical for conservation planning. This study was conducted in a peri-urban Inner Murchison Bay (IMB) catchment on the northern shores of Lake Victoria since most soil erosion studies in Sub-Saharan Africa have been focused on rural landscapes. The study sought to identify sediment sources by mapping erosion hotspots using the revised universal soil loss equation (RUSLE) model in appendage with field walks. RUSLE model was built in ArcGIS 10.5 software with factors including: rainfall erosivity, soil erodibility, slope length and steepness, land cover and support practices. The model was run, producing an erosion risk map and field assessments conducted to ground-truth findings and identify other hotspots. The percentage areas for RUSLE modelled erosion rates were: 66.8% for 0-2 tha-1year-1; 10.8% for 2-5 tha-1year-1; 10.1% for 5-10 tha-1year-1; 9% for 10-50 tha-1year-1 and 3.3% for 50-100 tha-1year-1. Average erosion risk was 7 tha-1year-1 and the total watershed erosion risk was 197,400 tyear-1, with croplands and steep areas (slope factor > 20) as the major hotspots (> 5 tha-1year-1). Field walks revealed exposed soils, marrum (gravel) roads and unlined drainage channels as other sediment sources. This study provided the first assessment of erosion risk in this peri-urban catchment, to serve as a basis for identifying mitigation priorities. It is recommended that tailored soil and water conservation measures be integrated into physical planning, focusing on identified non-conventional hotspots to ameliorate sediment pollution in Lake Victoria.

Land use contribution to spatiotemporal stream water and ecological quality: Implications for water resources management in peri-urban catchments

• Seasonal variability confounds land-use source contribution in peri -urban streams. • No robust ecological improvement despite implementation of Nature-based solution. • Nematode-based stress index reveals impacts and benefits of wastewater effluents. • Contaminant-bound particles and other chemicals stressors may be overlooked. Climate change and intensifying agricultural production and urbanization are central factors driving the global freshwater biodiversity decline. To design sustainable green transition schemes and support urban planning, a deeper understanding of the numerous interacting physicochemical and biogeochemical processes and their relation to ecological quality becomes essential. This study thus aims to explore links between hydrological regimes and patterns evident for key water quality parameters and benthic invertebrate indicators in a peri -urban catchment that has undergone several stream restoration projects. Results indicate significant seasonal variability in discharge and physico-chemical parameters confounding the identification of sources behind detrimental impacts on ecological quality, which may lead to the implementation of inappropriate mitigation strategies. Notably, sampling at the sub-catchment level underlined the dynamic contributions of both agricultural and urban-like areas for nitrogen and phosphorus, while non-volatile carbon was mainly exported from agricultural lands. Multivariate statistical methods were used to classify benthic macro- and meioinvertebrate (specifically nematode) taxa showing poor-to-moderate and poor-to-good ecological quality, respectively. Poor ecological quality was mostly found in the upstream part of the catchment, driven by a combination of low habitat quality and periodically impaired physico-chemical conditions (e.g. dissolved oxygen, temperature, and suspended solids). In addition, the nematode-based stress index NemaSPEAR[%] (expressing the proportion of species-at-risk within a sample and specifically sensitive to the chemical contamination), indicated a TSS-related transport of contaminants to the sediment. It could also reveal both the negative impacts of different urban features (low ecological quality just downstream of combined sewer overflows), as well as the potential benefits of wastewater effluents (i.e. good ecological quality, via well-treated flow contributions and limited fine sediment accumulation especially in summer) on the stream ecosystem. Our results highlight that the use of this indicator, in combination with high frequency monitoring are promising techniques to better link the dynamic impacts of land use and spatiotemporal changes in ecological quality.

Identification of High-Impact Uncertainty Sources for Urban Flood Models in Hillside Peri-Urban Catchments

Climate change, as well as increasing urbanization, lead to an increase in urban flooding events around the world. Accurate urban flood models are an established tool to predict flooding areas in urban as well as peri-urban catchments, to derive suitable measures to increase resilience against urban flooding. The high computational cost and complex processes of urban flooding with numerous subprocesses are the reason why many studies ignore the discussion of model uncertainties as well as model calibration and validation. In addition, the influence of steep surface (hillside) conditions on calibration parameters such as surface roughness are frequently left out of consideration. This study applies a variance-based approach to analyze the impact of three uncertainty sources on the two variables—flow and water depth—in a steep peri-urban catchment: (i) impact of DEM validation; (ii) calibration of the model parameter; (iii) differences between 1D/2D and 2D models. The results demonstrate the importance of optimizing sensitive model parameters, especially surface roughness, in steep catchments. Additional findings of this work indicate that the sewer system cannot be disregarded in the context of urban flood modeling. Further research with real heavy storm events is to be pursued to confirm the main results of this study.

Planning for green infrastructure using multiple urban ecosystem service models and multicriteria analysis

Unprecedented urban growth and extensive land use change especially in the Global South has placed increasing pressure on urban ecosystem services (UES). While there are numerous studies modelling and mapping ecosystem services, integrating the outputs of multiple ecosystem service assessments to provide recommendations for nature-based planning remains a challenge. The objective of this study is to characterise the spatial distribution of multiple UES in a rapidly urbanising catchment and to develop a systematic approach to facilitate the integration of UES into planning green infrastructure (GI). We used InVEST models to spatially quantify and map six realised UES (heat mitigation, runoff retention, sediment retention, scenic quality, urban recreation and agricultural production (i.e., ‘urban farming’)) in a rapidly developing, peri-urban catchment in Greater Kuala Lumpur, Malaysia. We identified synergies and tradeoffs between services and assessed the cooccurrence and overlap of hotspots between multiples services. Our assessment revealed that densely built areas generally had low UES provision. In the final step, we conducted a multicriteria analysis using ecosystem services-based criteria to identify locations for five GI strategies: conservation of headwaters, reforestation for biodiversity, development and conservation of urban parks and greening of built infrastructure (e.g., green walls and roofs). The selection of the appropriate GI strategy must consider the degree of urban development, especially in areas where multiple strategies were suitable. The findings of our study support GI planning within the catchment and the methods applied can be adapted to support sustainable land use management in urban areas globally.

Hydrological response of implementing green and blue infrastructure – study of a Brazilian metropolis

ABSTRACT Green and blue infrastructure (GBI) is an urban planning approach that can reduce and mitigate the impacts of urbanization in the water cycle. This study evaluates the hydrologic impacts of a possible deployment of GBI in a peri-urban catchment under pressure from urban development. Considering cost-effectiveness, the best combinations of GBI techniques were simulated and compared with a scenario with urban expansion. A hydrological model in SWMM was applied to simulate impacts of GBI in runoff and a Hec-RAS model to assess the impact on flood. A combination of lot areas treated by rooftop disconnection and roads treated by vegetative swales achieved the lowest cost and one of the highest effectiveness in runoff reduction. Despite the growth of impervious area by almost 100% from urban expansion, the GBI scenario would bring the hydrological conditions and total flooded area downstream closer to the current scenario ones.

Hydrological response of a peri-urban catchment exploiting conventional and unconventional rainfall observations: the case study of Lambro Catchment

Abstract. Commercial microwave links (CMLs) can be used as opportunistic and unconventional rainfall sensors by converting the received signal level into path-averaged rainfall intensity. As the reliable reconstruction of the spatial distribution of rainfall is still a challenging issue in meteorology and hydrology, there is a widespread interest in integrating the precipitation estimates gathered by the ubiquitous CMLs with the conventional rainfall sensors, i.e. rain gauges (RGs) and weather radars. Here, we investigate the potential of a dense CML network for the estimation of river discharges via a semi-distributed hydrological model. The analysis is conducted in a peri-urban catchment, Lambro, located in northern Italy and covered by 50 links. A two-level comparison is made between CML- and RG-based outcomes, relying on 12 storm/flood events. First, rainfall data are spatially interpolated and assessed in a set of significant points of the catchment area. Rainfall depth values obtained from CMLs are definitively comparable with direct RG measurements, except for the spells of persistent light rain, probably due to the limited sensitivity of CMLs caused by the coarse quantization step of raw power data. Moreover, it is shown that, when changing the type of rainfall input, a new calibration of model parameters is required. In fact, after the recalibration of model parameters, CML-driven model performance is comparable with RG-driven performance, confirming that the exploitation of a CML network may be a great support to hydrological modelling in areas lacking a well-designed and dense traditional monitoring system.

Investing in Urban Blue–Green Infrastructure—Assessing the Costs and Benefits of Stormwater Management in a Peri-Urban Catchment in Oslo, Norway

Cities are challenged by climate change impacts, such as extreme rainfall events that affect conventional urban water management systems via increased sewage water overflows resulting in water quality deterioration and urban floods causing infrastructure damage. Investments in blue–green infrastructure (BGI) are increasingly considered to address these issues. However, these should be cost-effective. In this study, the effectiveness of five different BGI strategies and one grey strategy are assessed for a peri-urban catchment area in Oslo (Grefsen) using a cost–benefit analysis. The strategies include (i) wadis; (ii) green roofs; (iii) raingardens, rain barrels and wadis; (iv) infiltration crates; (v) water squares, and (vi) a separate sewage system. Besides economic effectiveness, the study also aims to identify the proper protection level by comparing cost–benefit ratios and net benefits for 60-min rainfall events occurring once every 5, 20, and 100 years (M5, M20, and M100), concerning both the current situation and under future climate change (using the Representative Concentration Pathway 8.5). The analyses revealed the highest BC ratios for wadis (12.0–17.3), separate sewage systems (7.7–15.1), and a combination of raingardens, rain barrels, and wadis (1.6–2.3). Strategies dimensioned for less frequent but more intensive rainfall events yielded higher BC ratios. Results for infiltration crates were difficult to interpret and were found to be very sensitive to input parameters. The other strategies implied a negative BC ratio. The study concludes that investments in BGI in Grefsen, Oslo, can be positively judged from a social–economic perspective and provide suitable information for water-related decision makers to decide upon the strategy selection and the appropriate flood protection level.

Effect of Low-Impact Development Scenarios on Pluvial Flood Susceptibility in a Scantily Gauged Urban–Peri-Urban Catchment

AbstractDue to frequent pluvial flooding in different urban and peri-urban catchments worldwide, understanding the flooding situation is necessary for effective flood management. However, limited h...

Stormwater Detention Ponds in Urban Catchments—Analysis and Validation of Performance of Ponds in the Ouseburn Catchment, Newcastle upon Tyne, UK

The impact of stormwater drainage and detention ponds on flooding is assessed using statistical analysis and physically based computer simulation of a 45-year case study for a peri-urban catchment. In 1978, the 54 km2 Ouseburn catchment in Newcastle upon Tyne was impacted by the connection of a new 2.1 km2 residential development, directly to the Ouseburn River, via a stormwater drain, which reduced the time to peak and increased flood risk. Further residential developments of 1.6 km2 have been built since 2004, again with separated sewer systems, but this time linked to stormwater detention ponds before draining into the Ouseburn River. Detailed analysis of the data, confirmed with computer simulation, shows that in contrast with the 1978 intervention, these new developments had only a minimal effect on the flows in the Ouseburn River, in fact achieving a small reduction in peak flows for large events. This study assesses the post-construction efficiency of such systems, and we show that the stormwater detention ponds are working as designed.

Spatio-temporal variations in stable isotopes in peri-urban catchments: A preliminary assessment of potential and challenges in assessing streamflow sources

In peri-urban catchments where treated wastewater effluents are released into surface waters, knowledge of water sources and partitioning is important for mitigating water quality impacts, particularly during warm and dry periods with low discharge rates. Useful tools for the identification of water sources and flow paths under different wetness conditions are isotope tracers. However, very few studies have been carried out so far in urbanized catchments with complex land use distributions where natural headwaters interact with engineered components, e.g. effluent discharge. We undertook spatio-temporal sampling of isotopes, combined with water quality measurements, to complement climatic and hydrometric data across the 220 km2 peri-urban Erpe catchment near Berlin and assess seasonal changes in water sources during two exceptionally warm and dry years (2018 and 2019). The study showed a deterioration of water quality downstream of two municipal wastewater treatment plants; and the depletion of groundwater storage, along with isotopic enrichment of the stream, in summer 2019 (the second consecutive year with above-average temperatures and marked precipitation deficits). Streamflow in the upper reaches of the catchment was dominated by groundwater-fed tributaries in winter, but became increasingly dominated by wastewater in summer. In the lower catchment, flows were dominated by effluent from a large wastewater treatment plant, especially in summer. Young water from precipitation and urban storm runoff accounted for < 10 % of streamflow, despite the catchment being ~ 20 % urban. Similarities in the composition of wastewater and other runoff sources resulted in high uncertainties in end member separation and highlight the need for monitoring of other tracers to better characterize water impacts. Given climate change projections for the region are for drier, warmer summers, wastewater is likely to become a more dominant component of streams, which may have implications for environmental quality and ecosystem services.

Applications of a UV optical nitrate sensor in a surface water/groundwater quality field study.

Examples of the utility of UV optical nitrate sensors are provided for two field applications, investigating nitrate pollution in a lowland, peri-urban catchment. In one application, rapid, in-stream longitudinal nitrate surveys were made in summer and winter, by fixing an optical nitrate sensor operating in continuous measurement mode to a kayak that was paddled along 10km of the mainstem of the low-order stream in under 4h. Nitrate concentrations ranged between 3.45 and 6.39mg NO3-N/L. Nitrate hot-spots and cool-spots were mapped and found to relate to point discharges from spring-fed tributaries and land drains. Effective nitrate removal (dN/dx = - 0.08mgN/L/km), inferred to be from assimilation reactions, was evident in the summer dataset, but not the winter nitrate dataset. In a second application, the optical sensor was configured with appropriate technology to establish an autonomous and fully automated nitrate monitoring station. The station makes daily nitrate measurements of surface water, and groundwater, sampled from a cluster of four multi-level wells. Quarterly maintenance of the nitrate sensor has proven sufficient to keep measurement errors under 5%. Most nitrate variation has been recorded at or near the water table where concentrations have ranged between 3.47 and 5.88mg NO3-N/L, and annual maxima have occurred in late winter/spring, which coincides with when most nitrate leaching occurs from agricultural land. Seasonal nitrate patterns are not evident in groundwater sampled from 8-m depth, or deeper. High-frequency monitoring has revealed that some infra-season, short-term variability also occurs in shallow groundwater nitrate, driven by storm events, and which on occasion results in a temporary inversion of the groundwater nitrate-depth profile.

Improved hydrological modelling of urban catchments using runoff coefficients

The expansion of built-up areas within urban and peri-urban river catchments has the potential to increase flooding. Hydrological modelling of these catchments is an important tool to analyse and manage the increasing flood hazard, but it requires an understanding of the areas contributing to runoff from the urban parts of the catchment. This is difficult as in many catchments fine resolution data is not available and the connectivity of the impervious areas, sewer networks and the drainage network are not well understood. In this research, we present a novel approach for calculating the separate and combined sewer fractions for an urban river catchment and use these fractions to improve hydrological modelling of the catchment. The fractions are calculated using monthly runoff coefficients from paired rural/urban catchments, with the procedure carried out for 20 highly urbanized catchments within the UK. The calculated fractions have been compared with the OS MasterMap high-resolution land use data set and also verified against results obtained with the standard method of using hourly rainfall-runoff data in an event-based approach. Hydrological modelling using the physically-based Shetran system demonstrates improved results using the approach developed here. For urban and peri-urban catchments without fine resolution sewer and hydrological data, it is recommended that this new method should be applied before detailed hydrological modelling of the catchments is undertaken in order to evaluate the flows to the drainage network and determine the impact of urbanisation on the water balance.

Spatial Heterogeneity of Enteric Fever in 2 Diverse Communities in Nepal.

BackgroundTyphoid fever is endemic in the urban Kathmandu Valley of Nepal; however, there have been no population-based studies of typhoid outside of this community in the past 3 decades. Whether typhoid immunization should be prioritized in periurban and rural communities has been unclear.MethodsWe performed population-based surveillance for enteric fever in 1 urban catchment (Kathmandu) and 1 periurban and rural catchment (Kavrepalanchok) as part of the Surveillance for Enteric Fever in Asia Project (SEAP). We recruited individuals presenting to outpatient and emergency departments at 2 study hospitals with suspected enteric fever and performed blood cultures. Additionally, we conducted a household survey in each catchment area to characterize care seeking for febrile illness. We evaluated spatial heterogeneity in febrile illness, care seeking, and enteric fever incidence.ResultsBetween September 2016 and September 2019, we enrolled 5736 participants with suspected enteric fever at 2 study hospitals. Among these, 304 (5.3%) were culture positive for Salmonella Typhi (249 [81.9%]) or Paratyphi A (55 [18.1%]). Adjusted typhoid incidence in Kathmandu was 484 per 100 000 person-years and in Kavrepalanchok was 615 per 100 000 person-years. While all geographic areas for which estimates could be made had incidence >200 per 100 000 person-years, we observed spatial heterogeneity with up to 10-fold variation in incidence between communities.ConclusionsIn urban, periurban, and rural communities in and around Kathmandu, we measured a high but heterogenous incidence of typhoid. These findings provide some support for the introduction of conjugate vaccines in Nepal, including outside urban areas, alongside other measures to prevent enteric fever.

Land use and episodic rainfall as drivers of nitrogen exports in subtropical rivers: Insights from δ15N-NO3−, δ18O-NO3− and 222Rn

Ongoing land-use intensification in subtropical catchments is expected to release more inorganic nitrogen to downstream coastal waters similar to historical changes in temperate ecosystems. Here, we examined spatial and temporal drivers of stream nitrogen loads across a subtropical land-use gradient using the isotopic compositions of nitrate (NO3−-N) and radon (222Rn), a natural groundwater tracer. We investigated eleven subtropical creeks/rivers over contrasting hydrological conditions in Australia. NOx-N (nitrite (NO2−-N) + nitrate (NO3−-N)) accounted for 13.1%, 34.0%, and 42.6% of total dissolved nitrogen (TDN-N) in forest, peri-urban and agricultural creeks, respectively. Following an 80 mm rain event, loads of dissolved inorganic nitrogen (DIN-N) from agriculture catchments reached 368 mg N m−2 catchment area day−1. Forest and peri-urban catchments had aquatic TDN-N loads 17.8% and 31.1% of loads from agricultural catchments. Radon observations suggest that nitrogen and phosphorus loads were driven primarily by surface runoff rather than groundwater discharge. The δ15N-NO3− and δ18O-NO3− values in the agriculture, forest and peri-urban catchments indicate fertilisers and soil nitrogen as the main sources of NO3−-N. However, one of the catchments (Double Crossing Creek) received a mixture of recirculated greywater and chemical nitrogen fertilisers. Isotopic signatures imply significant NO3−-N losses via denitrification during dry conditions. Groundwater discharge played a minor role because regional aquifers were not contaminated by nitrogen. Overall, intensive agricultural land use and episodic rainfall events were the major spatial and temporal drivers of nitrogen loads.