ABSTRACT
Unlike the common use of only 'rainfall amounts' in indexing the drought in a place, this study have identified, verified and validated the potentials of nine (9) other precipitation effectiveness variables (PEV) that can equally reflect the drought conditions in any place. The 10 PEVs have been effectively combined to derive a 'at-site' operational drought index called the Conjunctive Precipitation Effectiveness Index (CPEI). A historical daily rainfall record from 1916-2003 for seven (7) stations in the SSRN was used to estimate CPEI for these stations. The CPEI obtained, using the 1023 possible arrangements for the various combinations of the 10 PEVs, were respectively statistically compared with the values for the Standard Precipitation Index (SPI), Rainfall Anomaly Index (RAI), Bhalmey-Mooley Drought Index (BMDI) and Palmer Drought Severity Index (PDSI). Results obtained showed that a maximum combination of six (6) PEVs gave an average correlation (r) value above 0.8. Those arrangements with r > 0.8 were further ranked and through a descriptive analysis, it was shown that the ultimate number of PEVs that can be effectively combined to get the optimum CPEI values for indexing the drought is three (3) PEVs for Gusau and Kano, five (5) PEVs for Sokoto and Maiduguri and four (4) for the rest stations under study. The drought conditions for over 50 years, in the SSRN, were therefore examined using the derived optimum CPEI index and other four indices. The results obtained for each of the indices compared very well with notable historical drought years. These preliminary applications show that most of the indices used can be considered as operational tools for a national drought watch system in the SSRN to quantify and characterize the drought conditions ix objectively. As the significant level of occurrence observed with one of these PEVs, i.e. dry spell occurrence within the wet season and year, for each of the station under study, initiated some concerns and interests. The study therefore also attempted to further analyze the incidence and distribution of the dry spell occurrences in the SSRN as a way of making suggestion on how the incessant spell in the SSRN can be well accommodated. The analysis involves an empirical analysis of the dry spell (EADS) in the SSRN. The results from the EADS provided an ample of information that can be used as guides for various agricultural applications.