Abstract
This paper examines the spatial and temporal characteristics of droughts during the rainy season (May-October) for 1965-2010 over northern Nigeria using monthly rainfall data from station rain gauges. The spatial distribution of rainfall is identified by Standardized Precipitation Index (SPI), which also characterizes specific temporal drought events. Mann-Kendall trend test is applied to analyze the changes in the drought trend and also to confirm the significance of the observed trends. The results of the analysis show major changes in the drought characteristics in northern Nigeria during the major dry episodes (1973-1983) and major wet episodes (1996-2010). For the period 1965-1985, all the stations showed a decreasing trend both in 3 and 6 months time scales. In contrast, 87.5% of the stations showed an increasing trend for the period 1985-2010, with Maiduguri, Nguru, Kano, Katsina and Yelwa showing significant increases, the prolonged dry spell in the 1970’s and 1980’s was shown clearly in some of the analyses. A large number of further observations would be required to put some of these findings on a finer basis for the Sahelian drought characterization. It is recommended that agricultural organizations and disaster management parastatals should be pro-active in drought adaptation and mitigation planning. Keywords : Standardized Precipitation Index, Spatial, Temporal, drought, Mann-Kendall, trend.
Highlights
Drought is very common in most countries of the world, those located in the arid and semiarid areas (Shahid and Hazarika, 2010; Wang et al, 2012a)
The results of the analysis show many years of drought as categorized into near normal (NN)with Standardized Precipitation Index (SPI) between 0.99 and -0.99, moderate drought (MD)with SPI between -1 and -1.49, severedrought (SD) with SPI between -1.5 and -1.99, extreme drought (ED)with SPI from -2 and below, below average rainfall with SPI index between 0 and below, and above normal drought (AN) with SPI index below -0.99.The 3 month SPI analysis indicate short and medium term moisture condition while the 6-month SPI could be associated with unusual stream-flows and reservoir levels which depends on the region and time of year (WMO 2012)
From the consideration of Mann-Kendall trend test we arrive at the conclusion that significant changes in rainfall patterns with predominantly drought in MayOctober
Summary
Drought is very common in most countries of the world, those located in the arid and semiarid areas (Shahid and Hazarika, 2010; Wang et al, 2012a). Drought is defined as a “period of insufficient rainfall either in time or in space”. It is caused by low rainfall, often associated with increased evaporation rates. This results in crop failure, enough to cause a severe shortage of food in a rural population (Betterton and Gadzama, 1987, Abdullahi, et al, 2006). Each year large areas and populations of the Sahel region of Nigeria have suffered from the impacts of drought (Oladipo, 1993; Adefolalu, 1986).Climate change projections show a likely associated increase in dry spell length and frequency of drought occurrence gradually spread southward especially to the Guinea Coast of Nigeria (Aremu and Olatunde, 2013). Drought can lead to an economic crisis, as rainfall is the main source of water for agricultural production, which is the main source of export in the area
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