Hamma Yacouba’s research while affiliated with Institut International d'ingénierie de l'eau et de l'environnement and other places

The basement aquifers in Burkina Faso are increasingly exposed to groundwater pollution, largely due to socio-economic activities and climatic fluctuations, particularly the reduction in rainfall. This pollution makes the management and understanding of these aquifers particularly complex. To elucidate the processes controlling this contamination, a methodological approach combining principal component analysis (PCA) and multivariate statistical techniques was adopted. The study analyzed sixteen physicochemical parameters from 58 water samples. The primary objective of this research is to assess groundwater quality and deepen the understanding of the key factors influencing the spatial variation of their chemical composition. The results obtained will contribute to better planning of preservation and sustainable management measures for water resources in Burkina Faso. The results show that three principal components explain 72% of the variance, identifying anthropogenic inputs, with two components affected by mineralization and one by pollution. The study reveals that the groundwater is aggressive and highly corrosive, with calcite saturation. Water-rock interactions appear to be the main mechanisms controlling the hydrochemistry of groundwater, with increasing concentrations of cations and anions as the water travels through percolation pathways. PCA also revealed that the residence time of the water and leaching due to human activities significantly influence water quality, primarily through mineralization processes. These results suggest that rock weathering, coupled with reduced rainfall, constitutes a major vulnerability for aquifer recharge.

This study evaluates the impact of sub-daily bias correction of gridded rainfall products (RPs) on the estimation rainfall erosivity in Burkina Faso (West African Sahel). Selected RPs, offering half-hourly to hourly rainfall, are assessed against 10 synoptic stations over the period 2001–2020 to appraise their accuracy. The optimal product (the integrated multi-satellite retrievals for GPM, IMERG) is further used as a reference for bias correction, to adjust the rainfall distribution in the remaining RPs. RPs-derived rainfall erosivity is compared to the global rainfall erosivity database (GloREDa) estimates. The findings indicate that bias correction improves the rainfall accuracy estimation for all RPs, in terms of quantitative, categorial metrics and spatial patterns. It also improved the distributions of rainfall event intensities and duration across all products, which further significantly improved the annual rainfall erosivity estimates at various timescales along with spatial patterns across the country, as compared to raw RPs. The study also highlights that bias correction is effective at aligning annual trends in rainfall with those in rainfall erosivity derived from RPs. The study therefore underscores the added value of bias correction as a practice for improving the rainfall representation in high-resolution RPs before long-term rainfall erosivity assessment, particularly in data-scarce regions vulnerable to land degradation.

Runoff simulation in highly anthropized catchments is complex, but essential for water management, especially in poorly gauged and data-scarce hydrosystems of the West African Sahel. This study aims to evaluate the effect of different calibration schemes on runoff simulation. The physically-based and semi-distributed hydrological SWAT (Soil and Water Assessment Tool) model is used to simulate daily runoff in the Nakanbé catchment at Wayen station in Burkina Faso (in the West African Sahel) over the period 2006-2012. Four (4) hydrometric stations (Dombré, Rambo, Ramsa and Wayen) gauging 4 nested catchments (ranging from 1060 to 21 178 km 2 in size) are considered. The added value of the consideration of nested catchments is assessed through the following 3 calibration schemes: one-site (OS) at the entire catchment outlet (Wayen); multi-sites with nested sub-catchments (MS1); and multi-sites without considering nested sub-catchments (MS2). The results indicate that OS and MS2 schemes perform well (KGE > 0.7, |PBIAS| < 3 %), with MS2 scheme being superior (KGE, PBIAS). However, the MS1 scheme (KGE = 0.68; PBIAS = −22.9 %) performed worse in comparison to the traditional OS scheme. The comparison of the three modelling schemes provides evidence that accounting for nested sub-catchments does not necessarily improve the quality of rainfall-runoff simulations. Yet, multi-site calibration should be favoured when catchments are not nested.

Rainfall erosivity is acknowledged as the most pivotal factor determining soil erosion and land degradagtion, especially in soil degradation prone environment such as sahelian landscapes. Yet, the long-term and accurate assessment of this factor is rarely carried out because of the prevalent of poor gauging networks and data scarcity on raifall observations in these contexts. This study therefore examines the potential use of seven (07) high-resolution gridded rainfall products (RPs) for the assessment of long-term annual rainfall erosivity in Burkina Faso in the West African Sahel. These RPs, providing half-hourly to hourly rainfall data, were evaluated against observations from synoptic stations over the period 2001-2020 to gauge their accuracy in daily, monthly, and yearly rainfall patterns. The best performing product (IMERG) was then utilized for bias correction of rainfall intensities and durations in the remaining RPs. The rainfall erosivity derived from the RPs was compared to the Global Rainfall Erosivity Database (GloREDa) estimates. The results suggest that IMERG most accurately represents rainfall patterns in Burkina Faso and consistently provides precise rainfall erosivity estimates. Furthermore, the bias correction effectively improves the RPs-derived rainfall erosivity. Finally, a trends analysis over the period 2001-2020 reveals stationary patterns in annual rainfall erosivity in most locations, except Ouagadougou (central region), where increasing trends in both annual rainfall and rainfall erosivity are observed. The study emphasizes the potential of high-resolution RPs for long-term rainfall erosivity assessment, and offers insights into the development of effective strategies for sustainable land management.

In Burkina Faso, human activities around water points in rural areas affect groundwater resources, which become unfit for consumption. Nearly 33.5% of boreholes are subject to point source pollution. The assessment of the evolution of such pollution should be monitored to assess groundwater quality. In addition, withdrawals for irrigation alone are estimated at 85%, i.e. 46% of the water demand, heightening the deterioration in quality while creating depression zones further leading to an increase in recharge. It is therefore critical to understand the evolution and fate of the transfer of pollutants in such environments. In this study, we aimed to model the transfer of pollutant and predict the future state of pollution using the MT3D-USGS Groundwater Solute Transport Simulator code through the Groundwater Modelling Software (GMS) over the period 2012-2062 (50 years). A mathematical model is further developed through inferential statistics and used as a surrogate model for comparison. The results showed that deterioration in water quality was more attributable to withdrawals, especially for Cyanide (Cn) and Arsenic (As). A rather slow degradation is reported for Lead (Pb), which extends over 22 km, and Fluoride (F), which extends from 4 to 10 km due to localized recharge. A faster degradation for Cn over a distance of 2 to 16 km and as from 3 to 11 km is also observed because of the geological setting of the subsoil. These results might assist decision-makers for the quantitative and qualitative management of groundwater resources, and the management of the basement aquifer in the area through the establishment of protection zones.

Drought is considered as a complex natural phenomenon that can have significant impacts on societies and economic sectors. Analysis of droughts helps in achieving optimal control of their effects and developing informed mitigation strategies. This study aims to investigate the relationships between meteorological and hydrological droughts in the Nakanbe River basin upstream Wayen hydrometric station (NRUW) in Burkina Faso. Based on monthly precipitation, potential evapotranspiration and streamflow records from 1971 to 2014, two meteorological drought indices, including the Standardized Precipitation Index and the Standardized Precipitation Evapotranspiration Index and one hydrological drought index, the Standardized Streamflow Index are evaluated at various time scales. Drought episodes are further characterized using the Run Theory. In addition, the propagation from meteorological drought to hydrological drought is investigated using cross-correlation and wavelet analyses, and the relationships between the two types of droughts are assessed through nonlinear models. The drought indices indicate distinct categories of droughts occurring in the NRUW with high frequency for the mild (31–40%) and moderate (7–12%) droughts. A significant downward drought trend is observed over the period 1971–2014 in the study area, while the highest correlations between meteorological and hydrological droughts are reported at 12-month time scale. Results highlighted the importance of the combined use of different meteorological drought indices for improve hydrological drought prediction. The relationships provided between the two types of droughts could further help in effective monitoring and prediction of hydrological drought events, especially in the context of scarcity of streamflow data and worsening climate.

This paper addresses the energy consumption in conventional shea butter production processes and its impact on sustainability. The socio-cultural significance of shea butter extraction and the environmental challenges posed by the demand for firewood in the Shea belt are considered. The aim of this study is to review the existing research on energy consumption in conventional shea butter production processes and provide insights into reducing energy consumption while improving sustainability. The specific objectives are to analyse critical operations in the process and quantify their electricity, water, and heat demand. The study identifies grinding shea kernels into a paste, fat recovery, and oil clarification as the key operations regarding electricity, water, and heat demand, respectively. The conventional production process heavily relies on firewood as an energy source, consuming approximately 8–10 kWh of heat per kg of produced crude shea butter when improved cookstoves/roasters are used. However, the use of three-stone cookstoves can double or even quadruple the heat demand. Valorisation of shea butter process residues, such as kneading sludges, has the potential to cover 50% of the required heat and replace significant amounts of firewood. However, this approach necessitates careful process design and potentially alternative fuels from the residues to ensure efficient combustion and reduce smoke emissions. The conventional shea industry generates a considerable amount of by-products, yet no systematic and efficient valorisation scheme is currently implemented. By implementing improved cookstoves and developing a comprehensive valorisation strategy for process residues, significant reductions in energy consumption and environmental impact can be achieved.

The precise estimation of reference evapotranspiration (ETo) is critical for water planning in agriculture. However, with the scarcity of data in developing countries, the use of the reference Penman–Monteith FAO-56 (FAO56-PM) equation to estimate ETo is difficult. Besides the quantification of this water balance component, its trends and sensitivities to climate variables are poorly assessed in such countries. In this study, an examination of ETo is carried out over the period 1988–2017 in Burkina Faso, a landlocked country in the West African Sahel. A gap-filling procedure is first used to estimate missing solar radiation data, in combination with bias-corrected climate data from MERRA-2 reanalysis. The gap-free dataset is therefore used to assess annual, seasonal trends in ETo and its dependant variables, as well as the sensitivities of ETo to its dependant variables. The results show a significant decrease (at Dori, northern region) and increase (Gaoua, southern region) in ETo. Also, solar radiation (rs) and maximum temperature (tx) have the highest effect on ETo, followed by relative humidity (rh) (with negative feedback), wind speed (ws) and minimum temperature (tn). Finally, 49 alternative methods of ETo estimation are calibrated (over 1988–2007), validated (over 2008–2017) using FAO56-PM as a reference and ranked out by performance index (PI). In general, combinatory methods (such as Kimberly–Penman equation) are the most accurate (PI = 0.38–0.61), followed by radiation methods (such as Trajkovic–Stojnic equation) which are satisfactory (PI = 0.21–0.76). Temperature methods (TMP) (such as Penman–Monteith temperature equation) and mass transfer methods (MTF) (such as Rohwer equation) perform worse in comparison (TMP: PI = 0.14–0.69/MTF: PI = − 0.49–0.40), with large underestimation by MTF methods (PBIAS = − 15.2–0.0%). Calibrated alternative equations such as Trajkovic–Stojnic, Penman–Monteith temperature and Kimberly–Penman are therefore recommended after FAO-56 PM for daily ETo estimation in Burkina Faso.

In this study, the Soil and Water Assessment Tool (SWAT) model is used to assess changes in surface runoff between the baseline (1995–2014) and future (2031–2050) periods in the Tougou watershed in Burkina Faso. The study uses a combination of land use maps (for current and future periods) and a bias-corrected ensemble of 9 CMIP6 climate models, under two warming scenarios. An increase in rainfall (13.7% to 18.8%) is projected, which is the major contributor to the increase in surface runoff (24.2% to 34.3%). The land use change narrative (i.e. conversion of bare areas to croplands) is expected to cause a decrease in surface runoff, albeit minor in comparison to the effect of future climate change. Similar findings are observed for annual maximum surface runoff. This study sheds light on the need to consider simultaneously future climate and land use in framing water management policies.