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

Water Resources Management and Modeling

Hydrology is the science that deals with the processes governing the depletion and replenishment of water resources of the earth's land areas. The purpose of this book is to put together recent developments on hydrology and water resources engineering. First section covers surface water modeling and second section deals with groundwater modeling. The aim of this book is to focus attention on the management of surface water and groundwater resources. Meeting the challenges and the impact of climate change on water resources is also discussed in the book. Most chapters give insights into the interpretation of field information, development of models, the use of computational models based on analytical and numerical techniques, assessment of model performance and the use of these models for predictive purposes. It is written for the practicing professionals and students, mathematical modelers, hydrogeologists and water resources specialists

Modeling climate and land use change impacts on water resources and soil erosion in the Dano catchment (Burkina Faso, West Africa)

The study assesses the effect of climate and land use change on water resources and soil ero-sion in the Dano catchment, Burkina Faso. Field measurements and derived process under-standing are complemented by a physically based modeling approach that is also used to simu-late the impact of land use and climate change. Extensive hydro-meteorological (e. g. precipitation, discharge), pedological (e. g. texture, bulk density) and soil erosion measurements (e. g. suspended sediment load) are investigated to gain knowledge on governing hydrological and soil erosion processes. Data from erosion plot measurements suggest statistically significant differences of runoff and soil erosion between differently used plots. The data and the retrieved understanding are used to setup and drive the physically based spa-tially distributed hydrological and soil erosion model SHETRAN. Statistical performance measures (R², NSE, KGE) range between 0.66 and 0.8 for the calibration and validation of dis-charge. Achieved quality measures of suspended sediment load are lower than for hydrology but comparable to other SHETRAN studies. The impact of land use and land cover (LULC) change on water resources and soil erosion is studied by applying observed and modeled land use maps to the period 1990 – 2030. The past LULC change is studied using land use maps of the years 1990, 2000, 2007 and 2013. Based on these maps future LULC scenarios were developed for the years 2019, 2025 and 2030. Ob-served and modeled climate data cover the period 1990 – 2030. The observed past and modeled future LULC maps are used to feed SHETRAN. The isolated and combined influence of LULC and climate change is investigated. The land use investigation from 1990 to 2013 suggests a decrease of savanna at annual rates of 1.15% while cropland and settlement areas have increased. The simulations that assumed a constant climate and a changing LULC show in-creasing water yield (3.9% – 77.5%) and mainly increasing specific sediment yield (-1.4% – 115.78%). The simulations that assume constant LULC and climate as changing factor indicate increases in water yield of 24.5% to 46.7% and in sediment yield of 31.1% to 54.7%. The com-bined application of LULC and climate change signals a clear increase in water yield (20.3% – 73.4%) and specific sediment yield (24.7% to 90.1%). Actual evapotranspiration is estimated to change across all simulations by -6.8% to 3.35%. The predicted climate change signal is investigated in detail by comparing the future period 2021 – 2050 with the historical period 1971 – 2000. Representative concentration pathways (RCP) 4.5 and 8.5 of six datasets of the CORDEX framework were used to study the future change in tem-perature and precipitation. Most of the used climate models predict an increase of temperature between 0.9°C and 2.0°C. Large uncertainties among the climate models exist regarding the climate change signal of future precipitation. Some climate models predict an increase (5.9% – 36.5%) others a decreased (6.4% – 10.9%) or a mixed signal. The application of the historical and future climate data to SHETRAN shows that future changes in discharge and specific sedi-ment yield follow the predicted precipitation signal. Simulated future discharge change ranges from -43% to +207%. The future change in sediment yield is in the same order

Land cover change analysis within the GLOWA Volta basin in West Africa using 30-meter Landsat data snapshots

Data on land cover and land cover change can be effectively inferred from multi-temporal satellite remote sensing data. Land cover change data is imperative for regional hydrological models and water budget estimates within large river basins or catchments. Especially in Africa, however, rigorous and standardized land cover change data is missing to parameterize hydrological models that are also used in a predictive capacity in the context of global change models or studies. Within the GLOWA Volta hydrological project in West Africa, land cover change was mapped for the Volta River basin, an area of 400.000 km2. We used 26 Landsat tiles from 1990 and from the period 2000 and 2001 correspondingly. A unique contextual fuzzy convolution filter was used to extract the linear land cover classes, whilst non-linear classes were mapped using a neural network classifier respectively for both time frames. The Landsat tiles were further augmented with daily and well corrected 250-meter MODIS timeseries observations, for the period from 2000 onwards. Data on soil texture and digital elevation model variables on streamflow and pit areas were also used. For the land cover definitions we adopted the standard Land Cover Classification System (LCCS) legend from the Food and Agricultural Organization (FAO). The change was calculated for each thematic LCCS land cover code and socio economic data from Ghana was used to verify the change vector for selected ‘hot spots of change’ areas. Mean accuracy for the change matrix and for all classes, based on the thematic accuracy of two mapped time frames respectively, was calculated at 54 percent certainty. We found that most ‘negative’ change (18 percent of the total mapped land cover) occurred from woody shrub to herbaceous vegetation and from woody shrub to herbaceous managed respectively. The second most dominant change (15 percent) was from woody closed to sparse woody. The third most dominate change (10 percent) occurred from woody closed to herbaceous. The fourth most change (6 percent) occurred from woody shrub to regularly flooded herbaceous managed (managed wetlands). An overall of 2 percent of the total land cover recorded a ‘positive’ change from managed areas in 1990, being both herbaceous and woody managed, to woody shrub (not managed) in 2000/2001. The ‘positive’ areas occurred in southern Ghana and predominately around urban areas. From the socio economic data analysis in the ‘hot spot’ areas in north eastern Ghana, most ‘negative’ change could be validated as being caused by the expansion of agricultural areas. The second most change in the hot spot area was caused by the expansion of rural clusters or urban areas, which was, area wise, directly related to the thinning of woody cover between 1990 and 2000/2001. We found the rates of deforestation and land conversion to agricultural areas to be dramatic in the GLOWA Volta basin, especially within the woody open to sparse (savanna) biome. Land cover conversion and dynamics can be effectively mapped using 30-meter Landsat data and other moderate resolution optical data feeds in conjunction with socio economic data. Especially the changes within wetland areas and along river systems as well as the thinning of woody cover densities at these measured rates influence or alter the flow dynamics of water and water availability in the GLOWA Volta basin