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

Abstract

The population of northern Côte 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 Côte 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.

Assessment of Meteorological Drought in Climate Variability Context within the Comoe River Transboundary Watershed

“…Although SPI can monitor wet periods, it is typically used to assess the length and magnitude of drought events. Reference [18] found the gamma distribution to fit well to the climatological precipitation time series. The gamma distribution is defined by its frequency or probability density function (Equation ( 1)).…”

“…The SPI calculation for any location is based on the long-term precipitation record for the desired period. This long-term record is fitted to a probability distribution, which is then transformed into a normal distribution so that the mean SPI for the location and desired period is zero [18]. Positive SPI values indicate greater than median precipitation, and negative values indicate less than median precipitation.…”

“…The most effective non-parametric tests for breaks in series are the Mann-Whitney test [22], the Free-CUSUM test and the parametric t-Student test. As for trend assessment, the non-parametric Mann- 2, and the related statistics are in [18]. Hydrological series are rarely symmetrical and the normality condition is not always verified for the application of parametric tests.…”

Characterization of Meteorological Droughts Occurrences in Côte d’Ivoire: Case of the Sassandra Watershed

“…Work on climate fluctuations in this part of the world has made it possible to identify periods of drought since the 1970s. In Côte d'Ivoire, this deficit situation has resulted in major climatic disruptions, including a significant drop in rainfall [6][7][8][9][10]. There has also been an abnormal extension of the dry season [11], irregular and uneven rainfall distribution and a significant decline in hydroelectric production [12].…”

Variabilités et Tendances des Paramètres Hydroclimatiques dans le Bassin Versant de la Rivière Banco au Sud de la Côte d’Ivoire

“…Le test de Mann-Kendall est une méthode robuste largement utilisée pour analyser les tendances dans les séries temporelles (Mann, 1945;Kendall, 1955). Plusieurs chercheurs ont utilisé cette approche pour différents paramètres hydrométéorologiques (Fossou et al,2015;Faye, 2016;Yao et al, 2018). Dans ce bassin, caractéristique de l'écosystème forestier tropical humide, la récession pluviométrique des dernières décennies fait peser une menace sur les ressources en eau.…”