Modeling climate and land use change impacts on water resources in the dano catchment (Burkina Faso, West africa)

This study investigated the impacts of climate and land use changes on water resources in the Dano catchment combining hydrological processes understanding, hydrological simulations and climate and land use scenarios application. The catchment covers about 195 km2 and is located in the Southwest of Burkina Faso in West Africa. The study area is characterized by an annual population growth of about 3% over the past decades. Based on intensive field investigations on soil hydraulic properties, instrumentation and monitoring of hydro-meteorological variables such as discharge, soil moisture, groundwater level, precipitation, temperature etc. the distributed and physically based hydrological simulation model WaSiM was successfully calibrated and validated for the catchment. Achieved model statistical quality measures (R2, NSE and KGE) ranged between 0.6 and 0.9 for total discharge, soil moisture, and groundwater level, indicating a good agreement between observed and simulated variables. Land use change assessment in the catchment over the period of 1990-2013 exhibited a decrease of natural and semi-natural vegetation at an annual rate of about 2%. Conversely, cropland, and to a lesser extend urban areas, have increased. Land conversion was attributed to population growth, changing in farming practices and environmental conditions. Four land use maps were used to build land use scenarios corresponding to different levels of land use change in the catchment. Application of the land use scenarios to the calibrated and validated hydrological model indicated that, compared to the land use status in 1990, the current situation leads to an increase in total discharge of about 17% and a decrease of actual evapotranspiration of about 5%. The results of simulations further showed that the increase in total discharge is related to high peak flow, suggesting an alteration of flood risk. Following field measurements that showed infiltration rates 1.2 times higher under semi-natural vegetation compared to cropland, land use change related effects on soil infiltration rate was integrated in the modeling of LULC change impact assessment. Model results with a refined soil (integrating this additional information) and a classic soil indicated similar trends in water balance components as a result of land use change. However slight differences of 0.5 to 20 mm/year in the water balance component were noticed between the two soil parameterization approaches. The integration of land use related effects on soil properties was suggested to render LULC change scenarios more plausible. The projected climate change signal in the catchment was analyzed using the representative concentration pathways 4.5 and 8.5 of six datasets of the COordinated Regional climate Downscaling Experiment-project. Compared to the reference period of 1971-2000, the climate models ensemble consistently projects an increased temperature of 0.1 to 2.6°C over the period 2021-2050. However, an agreement was not found among climate models with regards to precipitation change signal as projections for annual rainfall ranged between -13 and +18%. The application of the climate models ensemble in WaSiM showed future discharge change signals very similar to the projected precipitation change. Individual climate models showed opposite annual discharge change signals ranging from -40 to +50 %. On average, the climate models ensemble suggested a 7 % increase in annual discharge under RCP4.5 and a 2 % decrease under RCP8.5. The analysis of the catchment sensitivity to precipitation and temperature change indicated that discharge is more related to precipitation than to temperature as the environmental system of the catchment is water limited and not energy limited

Agricultural Expansion-Induced Infiltration Rate Change in a West African Tropical Catchment

Land use and land cover in the Dano catchment is characterized by a rapid conversion from seminatural vegetation (fallow) to agriculture (cropland). The study compares both the saturated (Ks) and the unsaturated (Kh) hydraulic conductivities under cropland and fallow in the catchment to gain insights into the effect of the current land use on soil water dynamics. Hydraulic conductivity was measured under forty-two (42) pairs of adjacent cropland-fallow plots using a Hood infiltrometer. Ks, Kh, bulk density, and soil texture were further compared using a paired two-tailed Student’s t-test (p=0.05). The results showed that both Ks and Kh are highly variable irrespective of the land use type (coefficient of variation > 100%). The results also showed that Ks was significantly higher (1.16-fold on average) under fallow compared to cropland. As for Kh, the results showed that, from −2 cm to zero tension heads (h), Kh under cropland and fallow is not significantly different; however, as the supplied tension decreases up to the saturation state, Kh under fallow becomes statistically higher compared to cropland. No significant difference was found between soil textures and bulk density under cropland and fallow meaning that the observed differences of Ks and Kh under cropland and fallow were caused by land use and not preexisting difference in texture. These results suggest an increasing risk of erosion, soil fertility reduction, and flood in the catchment because of agricultural land expansion

Non-Stationary Flood Discharge Frequency Analysis in West Africa

With climate change and intensification of the hydrological cycle, the stationarity of hydrological variables is becoming questionable, requiring appropriate flood assessment models. Frequency analysis is widely used for flood forecasting. This study aims to determine the most suitable models (stationary and non-stationary) for estimating the maximum flows observed at some stations spread across West Africa. A statistical analysis of the annual maximum flows in terms of homogeneity, stationarity, and independence was carried out through the Pettitt, modified Mann–Kendall, and Wald–Wolfowitz tests, respectively, to identify the stations whose flows are non-stationary. After that, the best-correlated climate covariates with the annual maximum flows of the non-stationary stations were determined. The covariates explored are the climatic indices of sea surface temperatures (SST). Finally, different non-stationary GEV models were derived by varying the scale and position parameters of the best-correlated index for each station. The results indicate that 56% of the annual maximum flow series are non-stationary. As per the Bayes information criterion (BIC) values, the performance of the non-stationary models (GEV, generalized extreme values) is largely greater than that of the stationary models. These good performances of non-stationary models using climatic indices open perspectives for the prediction of extreme flows in the study area

Testing the Robustness of a Physically-Based Hydrological Model in Two Data Limited Inland Valley Catchments in Dano, Burkina Faso

This study investigates the robustness of the physically-based hydrological model WaSiM (water balance and flow simulation model) for simulating hydrological processes in two data sparse small-scale inland valley catchments (Bankandi-Loffing and Mebar) in Burkina Faso. An intensive instrumentation with two weather stations, three rain recorders, 43 piezometers, and one soil moisture station was part of the general effort to reduce the scarcity of hydrological data in West Africa. The data allowed us to successfully parameterize, calibrate (2014–2015), and validate (2016) WaSiM for the Bankandi-Loffing catchment. Good model performance concerning discharge in the calibration period (R2 = 0.91, NSE = 0.88, and KGE = 0.82) and validation period (R2 = 0.82, NSE = 0.77, and KGE = 0.57) was obtained. The soil moisture (R2 = 0.7, NSE = 0.7, and KGE = 0.8) and the groundwater table (R2 = 0.3, NSE = 0.2, and KGE = 0.5) were well simulated, although not explicitly calibrated. The spatial transposability of the model parameters from the Bankandi-Loffing model was investigated by applying the best parameter-set to the Mebar catchment without any recalibration. This resulted in good model performance in 2014–2015 (R2 = 0.93, NSE = 0.92, and KGE = 0.84) and in 2016 (R2 = 0.65, NSE = 0.64, and KGE = 0.59). This suggests that the parameter-set achieved in this study can be useful for modeling ungauged inland valley catchments in the region. The water balance shows that evaporation is more important than transpiration (76% and 24%, respectively, of evapotranspiration losses) and the surface flow is very sensitive to the observed high interannual variability of rainfall. Interflow dominates the uplands, but base flow is the major component of stream flow in inland valleys. This study provides useful information for the better management of soil and scarce water resources for smallholder farming in the are

Chapitre 15. Fonctionnement hydrologique et hydraulique du bas-fond réaménagé de Bankandi

Contexte de l’étude Le projet Generia intervient au Burkina Faso dans la province du Ioba, région du Sud-Ouest, où une diversité de modèles d’aménagements de bas-fonds a été mise en œuvre pour une maîtrise partielle de l’eau. Le modèle le plus courant est celui des « diguettes en courbes de niveau » (DCN), généralement renforcées par empierrement avec possibilité de réguler l’eau par des pertuis. Conçu dans les années 1970 et 1980 pour faire face aux sécheresses survenues à cette période, ce ..

A multi-model approach for analysing water balance and water-related ecosystem services in the Ouriyori catchment (Benin)

Freshwater supply remains limited in West Africa due to lack of operational governance frameworks. In this study, the Water flow and balance Simulation Model (WaSiM) and the Soil and Water Assessment Tool (SWAT) were applied in the Ouriyori catchment (14.5 km2, Benin) to assess hydrological ecosystem services (HES) in terms of service flow and service capacity using the ecosystem accounting framework. The modelling exercises indicated satisfactory goodness-of-fit coefficients greater than 75% with an absolute bias of less than 25%. The HES capacity was in general higher than the HES flow for crop and household (surface/groundwater) water supplies, indicating that the catchment can potentially supply more water under optimal storage and management conditions. Positive and negative shifts in service capacities of crop water and household supplies were observed over the simulation period. These significant results can support sustainable interventions in securing water and food productions through increasing HES flow and capacity.</p