A New Statistical Approach to Assess Climate Variability in the White Bandama Watershed,Northern Cote d’Ivoire

The population of northern C&#244te d’Ivoire, especially in the white Bandama watershed, lives for majority in rural areas and depends on farming, which is mainly linked to climate variability. This study evaluates the trends within watershed’s hydro-climatic variables and their level of significance over the period 1950-2000. The methodological approach consists in applying successively standardized indexes to detect trends and breaks in hydro-climatic long-term data. The Mann-Kendall statistical test lets us know the trends significance and the Kendall-Theil Robust Line test reveals their magnitude. The Student’s t test underlines break years. Results show that although rainfall has decreased, this decline is not statistically significant. However, temperature and potential evapotranspiration have strongly rised and discharge was submitted to high decline. These changes in hydrometeorological variables appeared from 1970 to 1980. This study is different from others conducted on climate variability in the northern C&#244te d’Ivoire by the methodological statistical framework implemented and the understanding of significance level of climate trends. Until now, authors used the standardized index to detect trends in hydro-climatic parameters. For this work, we added the Mann-Kendall statistical test to assess the significance level of these trends at α = 5% and 10%. Then, the Kendall-Theil statistical test was used to highlight the trends magnitude and the student’s t test to know the break years.

Hydrogeochemical and Groundwater Quality Studies in the High Bandama Watershed at Tortiya (Northern of Côte d’Ivoire)

Hydrochemical and groundwater quality of High Bandama watershed were investigated through thirty-five (35) samples composed of boreholes, hand pump wells and traditional wells. The analysis of physico-chemical parameters shows that groundwater is acidic with pH ranges from 3.2 to 6.9 and mean of 5.4. Electrical conductivity (EC) values were generally low and minimum and maximum were respectively 77 μS/cm and 553 μS/cm with an average of 250.3 μS/cm. Major cations (Ca2+, Mg2+, Na+ and K+) were also generally low. Ca2+ and Mg2+ are being the most dominants cations with concentration values ranges from 4 - 56 mg/l and 0 - 55 mg/l respectively with mean value of 18.11 and 15.31 mg/l. HCO3? is the most dominant anion with minimum and maximum values ranging from 5 to 215 mg/l. According to WHO guidelines, groundwater quality is good for drinking. Piper diagram classified the hydrogeochemical facies into Ca-HCO3 (48.57%), Ca-Mg-HCO3 (31.43%), Ca-Mg-Cl (17.14%) and Na-Cl (2.86%) water type with one sample for Na-Cl. Compositional relation with plot of Ca + Mg versus HCO3 + SO4 and Chloro Alkaline Indice (CAI) confirms that the majority of groundwater samples (66.67%) exchange their ions Ca and Mg with Na and K from aquifer materials. Gibbs diagram showed that the rock-water interaction or weathering is the dominant process responsible of water chemistry.

Validation of Three Satellite Precipitation Products in Two South-Western African Watersheds: Bandama (Ivory Coast) and Mono (Togo)

Satellite precipitation products are widely used in different domain, in area where there is a lack in observation. These have different spatio-temporal resolutions consequently resulting in different precipitation amounts depending on the product. The present study validates three satellite products, namely the Climate Hazard group Infrared Precipitation with Stations (CHIRPS), the Climate Research Unit (CRU) and the Global Precipitation Climatology Project (GPCP) over Bandama and Mono river basins for 1981-2005 and 1981-2016 respectively by comparing them to the observation precipitation of the basin. The available studies are focused on the regional scale but not on a watershed scale for hydrological studies. The analysis reveals that all the products are strongly correlated to each other as well as to the observed data at basin level. The Lamb coefficient test shows that most all the chosen basin namely Bandama and Mono presents the same climatic indices. All the products present the same variability and trend as the observation at basins scale. By comparing those products to observation, CHIRPS product following by GPCP give the lowest mean absolute error (MAE) at annual and seasonal time scales while CHIRPS is followed by CRU at monthly scale. Overall, all products overestimate the precipitation at Bandama basin while they underestimate it over Mono river basin. The comparison over 1981-2017 period of the total annual precipitation increasing southern ward (from Sahel to the coastal zone) for all the three studied products which varies from 300 mm to 2400 mm/year. All the three products are not significantly different from one another and they all highlight the same areas of hotspot rainfall in the region. The same conclusion is made at monthly and seasonal scales. Therefore, any of these products especially CHIRPS can be used for study in this region due to its lowest bias and MAE.