Recent Rainfall Trend and Abrupt Changes Over Cavally Basin (West Africa)
Blé Anouma Fhorest Yao *
Geosciences and Environment Laboratory, Training and Research Unit in Environmental Science and Management, Nangui Abrogoua University, 02 BP 801 Abidjan 02, Côte d’Ivoire.
Emile Gneneyougo Soro
Geosciences and Environment Laboratory, Training and Research Unit in Environmental Science and Management, Nangui Abrogoua University, 02 BP 801 Abidjan 02, Côte d’Ivoire.
*Author to whom correspondence should be addressed.
Abstract
Aims: Analyze the recent variations in annual and monthly precipitation at 18 pluviometry stations in the Cavally river basin.
Place and Duration of Study: Data of month and annual rainfall data of 37 years (1980-2016) collected from the National direction of Meteorology for Ivory Coast and Guinea and from https://app.climateengine.org/climateEngine for Liberia.
Methodology: Statistical methods are used to highlight the evolution of cumulative annual rainfall and the distribution of the different seasons over the period 1980-2016. Hanning’s low pass, Mann-Kendall classic test, modified Mann-Kendall test, Mann-Kendall seasonal test and Standard Normal Homogeneity Test were applied to identify the existing trend direction and significance of change over time.
Results: The periods 1980-1996 and 1997-2016 could be considered as wet and dry periods respectively (with a rainfall deficit of 18% after the break in 1996). In addition, we observe a decrease in rainy days of strong accumulation that lead to a significant drop in total annual rainfall. Finally, an abnormal increase in rainfall during the dry season months and a decrease in rainfall during the rainy season months. This indicates an intra-seasonal irregularity (shortening of the rainy season and prolongation of the dry season) of precipitation.
Conclusion: The Hanning filter, M-K test and SNHT are non-parametric tests widely used in the study of climate trends. However, the additional consideration of serial autocorrelation (MM-K test) and seasonal trends (M-K-S test) allows to extend and refine the information on climate variability.
Keywords: Autocorrelation in trend significant, Cavally basin, recent rainfall evolution, spatio-temporal seasonal trend, statistical methods.