Detection of Hydrologic Trends and Variability in Transboundary Cavally Basin (West Africa)

Abstract

In a context of climate change and decreasing water resources, knowledge of recent flow evolution is essential. The present study focuses on the analysis of trends and spatio-temporal evolution of the Cavally River flow. In this study, 8 hydrometric stations, including 6 on the main river (Flampleu, Ity, Toulepleu, Tai, Fete and Tate) and two tributaries (N'Ce and Niebe) of the Cavally River were selected based on the availability and quality of long-term data. Annual and monthly data from these stations cover the period from 1980 to 2016. Statistical methods and the Hanning low-pass filter are used to highlight the evolution of the annual mean discharge and the spatial distribution of the different hydrometric seasons over the period 1980-2016. Hanning low-pass filter, Mann-Kendall tests (Classic, Modified and Seasonal) and SNHT were applied to detect and analyze the significance of change over time. The results of the statistical tests and Hanning's low-pass filter show the seasonal and annual change in flows. Stations in the northern part of the basin generally had a long dry period from 1980 to 2010 and a wet period from 2011 to 2016 and those in the central part had a wet period from 1980 to 2005 and dry period from 2006 to 2016. Stations in the central part have alternating normal periods. The significant increase in runoff during the dry season and some months of the rainy season was the main reason for the increase in annual runoff due to the considerable contributions of these seasons to the total runoff volume in the Cavally basin. Based on the results of the SNHT test for detecting abrupt changes in the series, about 62% of the series show a significant break, of which 60% are ascending at the 5% to 1% significance level. All observed breaks are generally located between 2000 and 2013.