STUDY OF THE RELATIONSHIP BETWEEN THE TEMPERATURE OF THE ATLANTIC OCEAN AND HYDROLOGICAL VARIABILITY IN THE N'ZI WATERSHED (Central-North Côte d'Ivoire)

Summary: The decline in rainfall experienced by the West African band in the decades 70 and 80 strongly affected the flow in the various sub-catchments. In order to better identify the different modes of variability, this work is dedicated to studying the relationship between the temperature of the Atlantic Ocean and changes in flow in the N'zi watershed. Continuous wavelet analysis was used for signal search signal in the Fêtêkro (1960-1997) and N'zianouan (1960-2010) hydrometric series. As for the consistency in wavelet, it made it possible to verify the link between the flow and Atlantic Ocean temperature indices (North Atlantic Temperature: TNA and South Atlantic Temperature: TSA). Continuous wavelet analysis shows a fairly marked variability overall in high frequencies (6 months to 1 year) and interannual (> 1 year). Thus, at the Fêtêkro station north of the basin, the annual scale (1 year) records half of the variability ready with an estimated signal at 46.09%.  For the N'zianouan station, 37.18% explains the variability of the signal. At this stage, the Fêtêkro station has a rather pronounced variability to the detriment of that of N'zianouan. At the level of low frequency variability, the N'zianouan station has a fairly pronounced variability from 1 to 7 years.  Periodicity (1 – 2; 2 – 4 years) marks the highest signal (19.78%). The station of Fêtêkro shows a signal in the decade 60 estimated at 9.46% at 2-year frequency. As for wavelet consistency, it indicates a strong influence of the TSA.  index. In Fêtêkro, a consistency in phase is perceptible from 2 years in the decades 60 and 70.  At the frequency (4-8 years), this logic is observed over the entire time series. At the station of N'zianouan, we observe this reality in the decades 60 and 80 at periodicity (2-6 years), and (7-9 years) from 1990. Therefore, the results of the coherence show that the TSA index strongly impacts the flow in the N'zi watershed.

Keywords: TSA, TNA, frequency, variability, N'zi watershed