Future climate projections for Southern Africa indicate an increase in the severity of droughts. Drought preparedness and management are important in such regions to minimise impacts on people and the environment. The aim of this study was to explore the responses of different institutions and actors to the 2015/2016 drought in the Komati catchment, and, consequently, what these experiences imply for drought management in the future. This was done through in-depth interviews with 30 key actors in the study area, including farmers, engineers, water managers and weather services personnel. Additionally, we examined data on precipitation, streamflows, reservoir levels, publications and communications in media, and minutes of the Komati Joint Operation Forum (KJOF) meetings. The results indicate that, whereas scientific tools for water resources management and drought forecasting exist in the catchment, the information generated using the tools was not sufficiently utilised in water (re) allocation decision making. This can be explained by the indifference of many stakeholders to early warning information, and by the preference of stakeholders to secure farm water supplies to minimize socio-economic losses in the short term. This resulted in late implementation of drought measures, when the drought had already started. Most of the measures implemented (i.e. water rationing and intensified monitoring) only helped partially in the crisis situation and did not tackle the root causes of vulnerability of the water users, especially for farmers. From the 2015/2016 drought we learnt that pro-active drought management could be supported through developing a drought management plan that is endorsed by all actors. More efforts are needed to improve how weather forecast information is packaged, communicated, deliberated and used by institutions (e.g. KJOF) and end-users (e.g. farmers). Moreover, this case study demonstrates that learning from past drought events is useful for improving evidence-based tools, policies and practices for drought management.@en

This paper presents a comprehensive and critical comparison of 10 disinfection methods of swimming pool water: chlorination, electrochemically generated mixed oxidants (EGMO), ultraviolet (UV) irradiation, UV/chlorine, UV/hydrogen peroxide (H2O2), UV/H2O2/chlorine, ozone (O3)/chlorine, O3/H2O2/chlorine, O3/UV and O3/UV/chlorine for the formation, control and elimination of potentially toxic disinfection byproducts (DBPs): trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), trihaloacetaldehydes (THAs) and chloramines (CAMs). The statistical comparison is carried out using data on 32 swimming pools accumulated from the reviewed studies. The results indicate that O3/UV and O3/UV/chlorine are the most promising methods, as the concentration of the studied DBPs (THMs and HANs) with these methods was reduced considerably compared with chlorination, EGMO, UV irradiation, UV/chlorine and O3/chlorine. However, the concentration of the studied DBPs including HAAs and CAMs remained much higher with O3/chlorine compared with the limits set by the WHO for drinking water quality. Moreover, the enhancement in the formation of THMs, HANs and CH with UV/chlorine compared with UV irradiation and the increase in the level of HANs with O3/UV/chlorine compared with O3/UV indicate the complexity of the combined processes, which should be optimized to control the toxicity and improve the quality of swimming pool water.@en

The limitation in quantity and quality of climate data, in particular rainfall measurements, directly affects the reliability of hydrological models, which negatively impacts on the quality of water resources planning and management. This is obviously true in poorly-gauged or in transboundary river catchments with limited practice of data sharing among the riparian states. Satellite-based and reanalysis rainfall products are increasingly recognised as a promising information source to supplement ground observations. This research aims to study the feasibility of using satellite-based and reanalysis rainfall data for rainfall-runoff modelling in the Sre Pok catchment-a poorly gauged catchment located in Vietnam and Cambodia. First, three selected rainfall products (Tropical Rainfall Measuring Mission-TRMM, CPC MORPHing Technique-CMORPH, and European Reanalysis-ERA-Interim) were compared against ground rainfall data of 13 rain-gauges, located inside and in the vicinity of the study catchment. The validation results show that the studied global datasets have a reasonably good correlation with ground observation at monthly time scale (NSE = 0.3 to 0.8, R2 = 0.4 to 0.8), but relatively poor correlation at daily scale (NSE = −0.4 to 0.3, R2 = 0.1 to 0.4). Next, a semi-distributed rainfall-runoff model based on HBV-Light was developed to validate these datasets in the Krong Ana sub-catchment of the Sre Pok. The results illustrate satisfactory to very good model performances at monthly time scale for the satellite-based and reanalysis rainfall inputs (NSE = 0.58 to 0.77, R2 = 0.59 to 0.78 for the calibration period from 2004 to 2007, while NSE = 0.59 to 0.80, R2 = 0.64 to 0.84 for the validation period from 2008 to 2010). However, only TRMM and ERA-Interim give acceptable results at daily scale with NSE = 0.52 to 0.67, R2 = 0.53 to 0.67 for the calibration period, and NSE = 0.41 to 0.61, R2 = 0.45 to 0.65 for the validation period. The study concludes that the tested satellite-based and reanalysis rainfall products, especially TRMM and ERA-Interim, could mimic reasonably well the monthly rainfall pattern in the study region. It also demonstrates a great opportunity to use satellite-based and reanalysis rainfall for runoff modelling at monthly time scale in the Sre Pok catchment and other poorly-gauged (transboundary) catchments in the region, for example in the Mekong and Red River Basins.@en

This paper investigates disinfection by-products (DBPs) formation and their relationship with governing factors in chlorinated swimming pools. The study compares concentrations of DBPs with WHO guidelines for drinking water quality recommended to screen swimming pool water quality. The statistical analysis is based on a global database of 188 swimming pools accumulated from 42 peer-reviewed journal publications from 16 countries. The mean and standard deviation of dichloroacetic acid and trichloroacetic acid were estimated as 282±437 and 326±517 μg L 1, respectively, which most often surpassed the WHO guidelines. Similarly, more than half of the examined pools had higher values of chloral hydrate (102±128 μg L 1). The concentration of total chloramines (650±490 μg L 1) was well above the WHO guidelines in all reported cases. Nevertheless, the reported values remained below the guidelines for most of the studied pools in the case of total trihalomethanes (134±160 μg L 1), dichloroacetonitrile (12±12 μg L 1) and dibromoacetonitrile (8 ±11 μg L 1). Total organic carbon, free residual chlorine, temperature, pH, total nitrogen and bromide ions play a pivotal role in DBPs formation processes. Therefore, proper management of these governing factors could significantly reduce DBPs formation, thereby, contributing towards a healthy swimming pool environment. @en

The variability of rainfall and climate, combined with land use and land cover changes, and variation in geology and soils makes it a difficult task to accurately describe the key hydrological processes in a catchment. With the aim to better understand the key hydrological processes and runoff generation mechanisms in the semi-arid meso-scale Kaap catchment in South Africa, a hydrological model was developed using the open source STREAM model. Dominant runoff processes were mapped using a simplified Height Above the Nearest Drainage approach combined with geology. The Prediction in Ungauged Basins (PUB) framework of runoff signatures was used to analyse the model results. Results show that in the headwater sub-catchments of Noordkaap and Suidkaap, plateaus dominate, associated with slow flow processes. Therefore, these catchments have high baseflow components and are likely the main recharge zone for regional groundwater in the Kaap. In the Queens sub-catchment, hillslopes associated with intermediate and fast flow processes dominate. However, this catchment still has a strong baseflow component, but it seems to be more impacted by evaporation depletion, due to different soils and geology, especially in drier years. At the Kaap outlet, the model indicates that hillslopes are important, with intermediate and fast flow processes dominating and most runoff being generated through direct runoff and shallow groundwater components, particularly in wetter months and years. There is a high impact of water abstractions and evaporation during the dry season, affecting low flows in the catchment. Results also indicate that the root zone storage and the parameters of effective rainfall separation (between unsaturated and saturated zone), quickflow coefficient and capillary rise, were very sensitive in the model. The inclusion of capillary rise (feedback from the saturated to unsaturated zone) greatly improved the simulation results.@en

Land use and land cover (LULC) changes are continuous phenomena, often driven by natural and anthropogenic factors. In Ethiopia, a conversion of forest and grass lands into cultivated and urbanized lands has been reported. While such changes are known to have multidirectional impacts on river flows, erosion and sedimentation, and the socio-economic situation within a catchment, there is a lack of assessment on the scale and rate of these changes, and consequent impacts. This study quantifies the rate of LULC in the Gumara catchment (1413 km2), an important tributary to Lake Tana in northwest Ethiopia. Landsat images of three years (1986, 2001 and 2015) were processed using the supervised classification method. An extensive field survey generated over 150 ground truth points, which were used in the classification and accuracy assessment process. Then, a conceptual rainfall-runoff model (HBV) was calibrated and validated to assess the impacts of LULC changes on water balance components - evapotranspiration, soil moisture, groundwater recharge and runoff. Additionally, the decadal means and trends of precipitation and discharge were analysed to further examine and quantify the observed changes (if any). A reasonably reliable LULC classification was achieved, with an overall accuracy of 90%. The results indicated that the catchment area under forest and grass land was about 11 and 18%, respectively, in 1986, which reduced to 5 and 10%, respectively, in 2015. In contrast, cultivated land increased from 70% in 1986 to 82% in 2015. Contrary to the expected impact of these LULC changes on hydrology, the HBV model, indicated only a slight change in the water balance components (±5%). Runoff and all other water balance components remained more or less stable despite considerable LULC changes. However, the uncertainties encountered in the modelling process (e.g. model structure, LULC representation) could have masked the LULC impacts on hydrology. This was supported by the significant increase in the observed discharge indicated by the statistical analysis, even in view of no substantial changes in precipitation. Therefore, LULC could cause considerable increase in discharge, which needs further testing (e.g. through physically based modelling with detailed inclusion of LULC processes).@en

Chemical hydrograph separation using electrical conductivity and digital filters is applied to quantify runoff components in the 1,640 km2 semi-arid Kaap River catchment and its subcatchments in South Africa. A rich data set of weekly to monthly water quality data ranging from 1978 to 2012 (450 to 940 samples per site) was analysed at 4 sampling locations in the catchment. The data were routinely collected by South Africa's national Department of Water and Sanitation, using standard sampling procedures. Chemical hydrograph separation using electrical conductivity (EC) as a tracer was used as reference and a recursive digital filter was then calibrated for the catchment. Results of the two-component hydrograph separation indicate the dominance of baseflow in the low flow regime, with a contribution of about 90% of total flow; however, during the wet season, baseflow accounts for 50% of total flow. The digital filter parameters were very sensitive and required calibration, using chemical hydrograph separation as a reference. Calibrated baseflow estimates ranged from 40% of total flow at the catchment outlet to 70% in the tributaries. The study demonstrates that routinely monitored water quality data, especially EC, can be used as a meaningful tracer, which could also aid in the calibration of a digital filter method and reduce uncertainty of estimated flow components. This information enhances our understanding of how baseflow is generated and contributed to streamflow throughout the year, which can aid in quantification of environmental flows, as well as to better parameterize hydrological models used for water resources planning and management. Baseflow estimates can also be useful for groundwater and water quality management.@en

Chemical hydrograph separation using electrical conductivity and digital filters is applied to quantify runoff components in the 1,640 km2 semi-arid Kaap River catchment and its subcatchments in South Africa. A rich data set of weekly to monthly water quality data ranging from 1978 to 2012 (450 to 940 samples per site) was analysed at 4 sampling locations in the catchment. The data were routinely collected by South Africa's national Department of Water and Sanitation, using standard sampling procedures. Chemical hydrograph separation using electrical conductivity (EC) as a tracer was used as reference and a recursive digital filter was then calibrated for the catchment. Results of the two-component hydrograph separation indicate the dominance of baseflow in the low flow regime, with a contribution of about 90% of total flow; however, during the wet season, baseflow accounts for 50% of total flow. The digital filter parameters were very sensitive and required calibration, using chemical hydrograph separation as a reference. Calibrated baseflow estimates ranged from 40% of total flow at the catchment outlet to 70% in the tributaries. The study demonstrates that routinely monitored water quality data, especially EC, can be used as a meaningful tracer, which could also aid in the calibration of a digital filter method and reduce uncertainty of estimated flow components. This information enhances our understanding of how baseflow is generated and contributed to streamflow throughout the year, which can aid in quantification of environmental flows, as well as to better parameterize hydrological models used for water resources planning and management. Baseflow estimates can also be useful for groundwater and water quality management.@en

In previous studies we have ascertained that inflows and seawater intrusion in the Shatt al-Arab River (SAR) are two key physical factors behind fluctuating and sharply escalating salinities observed in recent years. Such levels require a series of countermeasures and investigative studies to translate physical factors into a salinity dynamics model to understand the problem and its impact as these factors vary in location, time and quantity. A one-dimensional hydrodynamic and salt intrusion numerical model was applied to simulate the complex salinity regime in the SAR based on hourly time-series data for the year 2014. The model was used to analyse the impact of different management scenarios on salinity under different conditions. The results show a high correlation between seawater intrusion and river discharge. Increased use of water upstream and local water withdrawals along the SAR will increase seawater intrusion and salinity concentrations. Improving the quantity and quality of the upstream freshwater sources could reduce salinity levels. Discharging the drainage water into the river could be used to counteract the salt intrusion, considering that its location affects both the salinity distribution and extent. A scenario analysis based on a numerical model constructed for the longitudinal salinity variation associated with different sources in a tidal regime, can efficiently screen alternative water management strategies.@en

In previous studies we have ascertained that inflows and seawater intrusion in the Shatt al-Arab River (SAR) are two key physical factors behind fluctuating and sharply escalating salinities observed in recent years. Such levels require a series of countermeasures and investigative studies to translate physical factors into a salinity dynamics model to understand the problem and its impact as these factors vary in location, time and quantity. A one-dimensional hydrodynamic and salt intrusion numerical model was applied to simulate the complex salinity regime in the SAR based on hourly time-series data for the year 2014. The model was used to analyse the impact of different management scenarios on salinity under different conditions. The results show a high correlation between seawater intrusion and river discharge. Increased use of water upstream and local water withdrawals along the SAR will increase seawater intrusion and salinity concentrations. Improving the quantity and quality of the upstream freshwater sources could reduce salinity levels. Discharging the drainage water into the river could be used to counteract the salt intrusion, considering that its location affects both the salinity distribution and extent. A scenario analysis based on a numerical model constructed for the longitudinal salinity variation associated with different sources in a tidal regime, can efficiently screen alternative water management strategies.@en

ABSTRACT: Understanding the salinity variation caused by a combination of anthropogenic and marine sources is important for water resource management in heavily used rivers impacted by tidal influence. A quantitative analysis of intra-annual variability of salinity levels was conducted in the Shatt al-Arab River. Based on hourly records during 2014, the results showed high spatiotemporal variability in the range of 0.2–40.0 ppt. Similarities in salinity dynamics were used to divide the river course into four distinct spatial units to guide respective management actions. Salinity dynamics are influenced by different sources of saline water inflows and withdrawals associated with irrigation, industrial and municipal waste, marshes and by seawater intrusion. Adapting a simple interpolation approach, the measured distance of seawater intrusion was 80 km upstream the river mouth. Continuous monitoring of water quality can localize and assess the relative impact of the various salinity sources at different times. Managing seawater intrusion and any local effects should take into account variations in quantity and quality of irrigation return flows and wastewater discharges.@en

ABSTRACT: Understanding the salinity variation caused by a combination of anthropogenic and marine sources is important for water resource management in heavily used rivers impacted by tidal influence. A quantitative analysis of intra-annual variability of salinity levels was conducted in the Shatt al-Arab River. Based on hourly records during 2014, the results showed high spatiotemporal variability in the range of 0.2–40.0 ppt. Similarities in salinity dynamics were used to divide the river course into four distinct spatial units to guide respective management actions. Salinity dynamics are influenced by different sources of saline water inflows and withdrawals associated with irrigation, industrial and municipal waste, marshes and by seawater intrusion. Adapting a simple interpolation approach, the measured distance of seawater intrusion was 80 km upstream the river mouth. Continuous monitoring of water quality can localize and assess the relative impact of the various salinity sources at different times. Managing seawater intrusion and any local effects should take into account variations in quantity and quality of irrigation return flows and wastewater discharges.@en

This study provides a hydrology based assessment of (surface) water resources and its continuum of variability and change at different spatio-temporal scales in the semi-arid Karkheh Basin, Iran, where water is scarce, competition among users is high and massive water resources development is under way. The study reveals that the ongoing allocation planning is not sustainable and essentially requires reformulation, with consideration of spatio-temporal variability and observed trends in the streamflows regarding flood intensification and decline in low flows. The development of innovative methods for quantification of the hydrological fluxes (i.e., regionalization of model parameters based on similarity of the flow duration curve and the use of areal precipitation input in the hydrological modeling) helped better understanding and modeling the basin hydrology. The investigation of scenarios for upgrading rain-fed areas to irrigated agriculture, using SWAT, recommends the promotion of in-situ soil and water conservation techniques. Conversion of rain-fed areas to irrigation causes significant reduction in the downstream flows, and requires additional considerations such as less development in the upper catchments, practicing supplementary irrigation and developing water storage. The knowledge generated is instructive for hydrological assessment and its use in water resources planning and management in the river basin context.@en