Teleconnection of spatial variations of effective onset of rainfall and ENSO\IOD over savanna zones of Nigeria

Abstract

This study characterised the spatio-temporal patterns of effective rainfall onset dates, their variability and their relationship with ENSO/IOD over Savanna zones of Nigeria. Daily rainfall and ENSO/IOD data for the period 1971–2015 were used. The IntraSeasonal Rainfall Monitoring Index (IRMI) was applied to identify and classify effective rainfall onset dates. The classified effective rainfall onset dates were subjected to the Mann-Kendall trend test. The coefficient of variation (CV) was employed for the variability test, while Pearson’s product-moment correlation was employed to establish an association between variables. The results indicate a variation in the effective start of rainfall of 15 days, and 30–60 days, in the Guinea Savanna and SudanoSahelian Savanna zones, respectively, between the western and eastern axes. The onset date trend test revealed that stations in the guinea savanna zone tended to have later effective onset dates while stations in the Sudano-Sahelian savanna zone tended to have earlier onset dates of rainfall. The correlation test showed a significant and insignificant positive relationship between effective rainfall onset dates and the ENSO/IOD phase, particularly in the stations across the guinea savanna zones of the study area. It is expected that this information on the variability of effective rainfall onset dates, when provided in aid of rain-fed agriculture, could support decision-making on crop types to be cultivated and on the planning of sowing dates across the study area. These findings are of high importance to the entire West African sub-region, including other parts of the world that share similar monsoon rainfall and physical characteristics of these savanna zones.