AN ASSESSMENT OF DROUGHT IN THE SUDANO - SAHELIAN ECOLOGICAL ZONE OF NIGERIA

Abstract

Drought is a natural hazard characterized by lower than normal precipitation which is insufficient to meet demands of human activities and the environment. It occurs in both high and low rainfall areas and virtually all climatic regions, although in the past, drought was only associated with arid, semi-arid and desert fringes when definition was based only on absolute rainfall amounts. With drought spells now being associated with onset and cessation dates of rains and length of the rainy season, it is better defined as ineffectiveness of precipitation. A quantitative assessment of drought characteristics and their associated variability in the Sudano-Sahelian Ecological Zone (SSEZ) of Nigeria was carried out. Monthly Rainfall data for seven selected station which are Kano, Nguru, Sokoto, Yelwa, Katsina, Dutse and Maiduguri which spans a period of 50years (1961-2010) collected from the Nigeria Meteorological Agency were used. The long term rainfall records were analyzed for drought using standardized precipitation index (SPI), Palmer Drought Severity Index (PDSI) and the Specific Water Consumption (SWC).The results of the SPI, PDSI and SWC analysis have shown that there are two distinct trends: below normal rainfall and above normal rainfall in the entire stations. The results of SPI and PDSI analysis revealed that there were several drought years in the study area within the study period. These were classified into mild, moderate, severe and extreme drought conditions. 20years of total drought occurrences was noted within 1961-2010 in the study area. The prominent extreme drought years across the region were 1973, 1983 and 1987 in which the drought of 1980s proved to be more devastating due to its duration and severity. SPI analysis for 3, 6, and12 month was carried out. According the Nigeria Meteorological Agency classification that 3months represent meteorological and agricultural drought, 6months represent hydrological drought and 12months represent socio-economic drought. The analysis revealed distinct period of negative and positive values of SPI index in which the negative values indicate occurrence of drought and the positive values implies no drought or wet conditions. The SWC values obtained shows that the Sudano-Sahelian Ecological Zone is a dry area where high irrigation is needed. The SWC index of drought is the best quantitative measure of precipitation ineffectiveness that makes use of rainfall amount, onset, cessation and length of rainy season characteristics and evaporation. The study has provided a useful information and pro- active intervention to reduce the impact of drought in this zone which will be helpful to effectively plan for rain-fed agriculture within the Sudano-Sahelian Ecological Zone of Nigeria.