Effect of single and multi-site calibration techniques on hydrological model performance, parameter estimation and predictive uncertainty: a case study in the Logone catchment, Lake Chad basin

Understanding hydrological processes at catchment scale through the use of hydrological model parameters is essential for enhancing water resource management. Given the difficulty of using lump parameters to calibrate distributed catchment hydrological models in spatially heterogeneous catchments, a multiple calibration technique was adopted to enhance model calibration in this study. Different calibration techniques were used to calibrate the Soil and Water Assessment Tool (SWAT) model at different locations along the Logone river channel. These were: single-site calibration (SSC); sequential calibration (SC); and simultaneous multi-site calibration (SMSC). Results indicate that it is possible to reveal differences in hydrological behavior between the upstream and downstream parts of the catchment using different parameter values. Using all calibration techniques, model performance indicators were mostly above the minimum threshold of 0.60 and 0.65 for Nash Sutcliff Efficiency (NSE) and coefficient of determination (R 2 ) respectively, at both daily and monthly time-steps. Model uncertainty analysis showed that more than 60% of observed streamflow values were bracketed within the 95% prediction uncertainty (95PPU) band after calibration and validation. Furthermore, results indicated that the SC technique out-performed the other two methods (SSC and SMSC). It was also observed that although the SMSC technique uses streamflow data from all gauging stations during calibration and validation, thereby taking into account the catchment spatial variability, the choice of each calibration method will depend on the application and spatial scale of implementation of the modelling results in the catchment

Analysis of rainfall variability in the Logone catchment, Lake Chad basin

The socio-economic consequences posed by climate change in Africa are giving increasing emphasis to the need for trend analysis and detection of changes in hydro-climatic variables in data deficient areas. This study analyzes rainfall data from seventeen rain gauges unevenly distributed across the Logone catchment in the Lake Chad basin (LCB) over a fifty-year period (1951-2000). After quality control of the rainfall data using homogeneity tests, non-parametric MannKendall (MK) and Spearman rho tests were applied to detect the presence of trends. Trend magnitude was calculated using Sen’s Slope Estimator. Results of the homogeneity test showed that rainfall was homogeneous across the catchment. Trend analysis revealed the presence of negative trends for annual rainfall at all the stations. Results of long term trend analysis at a monthly time scale revealed the presence of statistically insignificant positive trends at 32% of the stations. Spatially, the analysis showed a clear distinction in rainfall magnitude between the semi-arid and Sudano zones. The slope of the trend lines for annual rainfall averaged over the respective zones was higher in the semi-arid zone (-4.37) compared to the Sudano zone (-4.02). However, the station with the greatest reduction in annual rainfall (-8.06 mm) was located in the Sudano zone

Exploring the socioeconomic determinants of water security in developing regions

The objectives of this study are two fold: first, to develop a composite water security metric to assess water security at a national scale, and second, to explore the determinants of water security at the same scale in three developing regions – Africa, Asia-Pacific and Latin America and the Caribbean (LAC). The water security index (WSI) was developed using three biophysical (water availability, climate risk and ecosystem vitality) and two socioeconomic (water accessibility and integrated water resources management) variables. Five independent variables (governance, gross domestic product (GDP) per capita, percentage of urban population, official development assistance for water and sanitation services (ODA-WSS) and female primary school completion rate) were used to explore the determinants of water security. Results show that >90% of countries in Africa and the Asia-Pacific regions are water-insecure, whereas most countries in LAC are water-secure except Haiti, Guatemala and Nicaragua. Statistical analyses show that GDP per capita, female primary school completion rate and governance are the key determinants of water security. This study provides empirical evidence on the link between female primary school completion rate and water security. Results further show a strong correlation between water security and ODA-WSS in the region with a higher ODA-WSS per capita than in regions with a low ODA-WSS per capita. This suggests that increasing ODA-WSS per capita may enhance water security in developing regions

Evaluating global reanalysis datasets as input for hydrological modelling in the Sudano-Sahel region

This paper investigates the potential of using global reanalysis datasets as input for hydrological modelling in the data-scarce Sudano-Sahel region. To achieve this, we used two global atmospheric reanalyses (Climate Forecasting System Reanalysis and European Center for Medium-Range Weather Forecasts (ECMWF) ERA-Interim) datasets and one global meteorological forcing dataset WATCH Forcing Data methodology applied to ERA-Interim (WFDEI). These datasets were used to drive the Soil and Water Assessment Tool (SWAT) in the Logone catchment in the Lake Chad basin. Model performance indicators after calibration showed that, at daily and monthly time steps, only WFDEI produced Nash Sutcliff Efficiency (NSE) and Coefficient of Determination (R2) values above 0.50. Despite a general underperformance compared to WFDEI, CFSR performed better than the ERA-Interim. Model uncertainty analysis after calibration showed that more than 60% of all daily and monthly observed streamflow values at all hydrometric stations were bracketed within the 95 percent prediction uncertainty (95PPU) range for all datasets. Results from this study also show significant differences in simulated actual evapotranspiration estimates from the datasets. Overall results showed that biased corrected WFDEI outperformed the two reanalysis datasets; meanwhile CFSR performed better than the ERA-Interim. We conclude that, in the absence of gauged hydro-meteorological data, WFDEI and CFSR could be used for hydrological modelling in data-scarce areas such as the Sudano-Sahel region

Evaluating global reanalysis precipitation datasets with rain gauge measurements in the Sudano-Sahel region: case study of the Logone catchment, Lake Chad Basin

Africa has a paucity of long(term reliable meteorological ground station data and reanalysis products are used to provide the climate estimations that are important for climate change projections. This paper uses monthly observed precipitation records in the Logone catchment of the Lake Chad Basin (LCB) to evaluate the performance of two global reanalysis products: the Climate Forecasting System Reanalysis (CFSR) and ERA Interim datasets. The two reanalysis products reproduced the monthly, annual and decadal cycle of precipitation and variability relatively accurately albeit with some discrepancies. The catchment rainfall gradient was also well captured by the two products. There are good correlations between the reanalysis and rain gauge datasets though significant deviations exist, especially for CFSR. Both reanalysis products overestimated rainfall in 68% of the rain gauge stations. ERA Interim produced the lowest bias and mean absolute error (MAE) with average values of 2% and 6.5mm/month respectively compared to 15% and 34mm/month for the CFSR. However, both reanalysis products systematically underestimated annual rainfall in the catchment during the period 1997(2002 for ERA(Interim and 1998(2000 for CFSR. This research demonstrates that evaluating reanalysis products in remote areas like the Logone catchment enables users to identify artefacts inherent in reanalysis datasets. This will facilitate improvements in certain aspects of the reanalysis forecast model physics and parametrisation to improve reanalysis dataset quality. Our study concludes that the application of each reanalysis product in the catchment will depend on the purpose for which it is to be used and the spatial scale required

Use of continuous simulation model (COSIMAT) as a complementary tool to model sewer systems: a case study on the Paruck collector, Brussels, Belgium

Episodic Combined Sewer Overflow (CSO) discharges effectively control the ecological status of receiving water bodies. Hydrodynamic models like the Storm Water Management Model (SWMM) are often used to model the CSO events. However, such detailed models are computationally demanding especially when a long‐term simulation of a complex system is required. Considering this, we developed an alternative simple continuous simulation model (COSIMAT) using the SIMULINK™ module in MATLAB™ as a means of solving the issue of computational time associated with the detailed models. The COSIMAT model was tested against a detailed model set up on the SWMM. The Paruck collector – one of the major Collector of the Brussels’ sewer system was used as an example case. Results showed that the accuracy of the simplified COSIMAT model was comparable to that of the detailed hydrodynamic model (SWMM) with a significant reduction of computational time by a factor of 8. We believe such alternative approaches would be useful to replace a computationally demanding model component of an integrated modelling system of a complex sewer system

Changes in climate, vegetation cover and vegetation composition affect runoff generation in the Gulf of Guinea Basin

Although considerable effort has been deployed to understand the impact of climate variability and vegetation change on runoff in major basins across Africa, such studies are scarce in the Gulf of Guinea Basin (GGB). This study combines the Budyko framework and elasticity concept along with geospatial data to fill this research gap in 44 nested sub-basins in the GGB. Annual rainfall from 1982 to 2021 show significant decreasing and increasing trends in the northern and southern parts of the GGB, respectively. Annual potential evapotranspiration (PET) also shows significant increasing trends with higher magnitudes observed in the northern parts of the GGB. Changing trends in climate variables corroborates with shift to arid and wetter conditions in the north and south, respectively. From 2000 to 2020 vegetation cover estimated using enhanced vegetation index (EVI) shows significant increasing trends in all sub-basins including those experiencing a decline in annual rainfall. Vegetation composition measured using vegetation continuous fields (VCFs) from 2000 to 2020 show an increase in tree canopy cover (TC), a decline in short vegetation cover and marginal changes in bare ground cover (BG). Elasticity coefficients show that a 10% increase in annual rainfall and PET may lead to a 33% increase and 24% decline in runoff, respectively. On the other hand, a 10% increase in EVI may lead to a 4% decline in runoff while a 10% increase in TC, SV and BG may reduce runoff by 4% and increase runoff by 3% and 2%, respectively. Even though changes are marginal, decomposing vegetation into different parameters using EVI and VCFs may lead to different hydrological effects on runoff which is one of the novelties of this study that may be used for implementing nature-based solutions. The study also demonstrates that freely available geospatial data together with analytical methods are a promising approach for understanding the impact of climate variability and vegetation change on hydrology in data-scarce regions

Understanding links between water scarcity and violent conflicts in the Sahel and Lake Chad Basin using the water footprint concept

Whilst there are several empirical studies linking water scarcity and violent conflicts, existing quantitative studies use mostly climate and environmental variables even though such variables have been shown to not be strong predictors of water conflicts by some studies. The aim of this study was to use the water footprint concept and the Falkenmark index to identify water scarcity hotspots at the sub-national scale and to understand the links between water scarcity and violent conflicts in the Sahel and Lake Chad Basin over a period of two decades (2000–2021). We achieve this by developing five water scarcity metrics at a monthly timescale using runoff, soil moisture, potential evapotranspiration, water consumption and demographic data. The developed metrics show high levels of water scarcity across the study area during the dry, pre-monsoon and post-monsoon seasons. Analyses further reveal high green water scarcity (GWS) (soil moisture deficit) and low Falkenmark index scores (water stress) during the dry, pre-monsoon and post-monsoon seasons, across all reported water conflict locations. This suggest that there is an indirect link between GWS, the Falkenmark index scores and water conflicts. Results from this study may be used to enhance water management, mitigate, and prevent water conflicts in the study area and likewise the methodology adopted may be used to address water scarcity and conflicts in other region

What Determines Behaviours Towards Water Resources Management in a Rural Context? Results of a Quantitative Study

Recent environmental policies introduced to safeguard the quality of water resources have focussed on encouraging pro-environmental behaviours (PEB). This has resulted in a considerable volume of research output that seeks to investigate the determinants of PEB in the context of water resources management. However, there is a paucity of literature exploring the topic within the developing country context, though evidence suggests that these regions record the highest rates of water resource pollution. This limits our understanding of the determinants of PEB and thus constrains our ability to develop and implement effective policies to encourage uptake of PEB. Following this, we apply the Theory of Planned Behaviour to explore the determinants of PEB, using structural equation modelling to analyse survey data from rural Ghana. The evidence supports the hypothesis that attitudes and perceived behavioural control affects intentions, and this translates into pro-environmental behaviour. Results further indicate that attitude and perceived behavioural control have a strong explanatory power in people’s intentions, and intentions are influential drivers of pro-environmental behaviour. An explicit recognition of the role of situational factors could offer a profound understanding of the determinants of behaviours that promote water resources management and support the development and implementation of policies aimed at safeguarding the quality of water resources

Evaluating the accuracy of gridded water resources reanalysis and evapotranspiration products for assessing water security in poorly gauged basins

Achieving water security in poorly gauged basins is critically hindered by a lack of in situ river discharge data to assess past, current, and future evolution of water resources. To overcome this challenge, there has been a shift toward the use of freely available satellite and reanalysis data products. However, due to inherent bias and uncertainty, these secondary sources require careful evaluation to ascertain their performance before being applied in poorly gauged basins. The objectives of this study were to evaluate river discharge and evapotranspiration estimates from eight gridded water resources reanalysis (WRR), six satellite-based evapotranspiration (ET) products, and ET estimates derived from complimentary relationship (CR–ET) across eight river basins located in Central–West Africa. Results highlight strengths and weaknesses of the different WRR in simulating discharge dynamics and ET across the basins. Likewise, satellite-based products also show some strength and weaknesses in simulating monthly ET. Our results further revealed that the performance of the different models in simulating river discharge and evapotranspiration is strongly influenced by model structure, input data, and spatial resolution. Considering all hydrological model evaluation criteria, FLDAS-Noah, Lisflood, AWRAL, and Terra were among the best performing WRR products while for ET estimates, FLDAS-Noah, Terra, GLEAM3.5a and 3.5b, and PMLV2 outperformed the rest of the products. Given the plethora of WRR and ET products available, it is imperative to evaluate their performance in representative gauged basins to identify products that can be applied in each region. However, the choice of a particular product will depend on the application and user requirements. Taking this together, results from this study suggest that gridded WRR and ET products are a useful source of data for assessing water security in poorly gauged basins