Abstract
This study was carried out to evaluate the drought occurrence and its implication on vegetation cover over the Sudano-Sahelian zone of the Northern part of Nigeria. Monthly mean Rainfall data for the period 40 years (1971-2010) were obtained from Nigeria Meteorological Agency (NIMET) for each of the meteorological stations present and functioning in this region for climatic analysis. Standardized Precipitation Index (SPI) was used to analyze drought occurrence on a time scale of five (5) months that cover the period of raining season over the study area. Also Satellite data over the selected part of the study area for three different epochs, 1986, 2000 and 2005 were used for vegetation response analysis. The SPI values were interpolated using Inverse Distance Weighted (IDW) interpolation technique in ArcGIS 9.3 to generate Drought Spatial Pattern Map for each selected modeled years. The vegetation response indicators used are land cover maps and Greenness Index (GI) maps. Land cover categories were classified into five levels: Dense Vegetation, less dense Vegetation, Settlement/built up, Bare Surface and Water body. The results based on the ground truth (rainfall) data show that many years of drought episode were experienced over the study area. On the other hand, the prime indicators (Land cover and GI maps) used in this study also depicts the changes that took place over the study area in response to this climatic anomaly (drought) and it could be noted that there was dramatic reduction in the occurrence towards the end of the last two decade, 1990-1999, which simply indicated improvement in rainfall even in 2000 and the later years.
Highlights
Most studies have revealed that several drought episodes hit the northern part Nigeria and left the region in a pitiable socio-economic condition
The circulation patterns in the tropics are strongly affected by heat inputs from such sources as warm ocean surfaces through the latent heat released in deep cumulus convection [4], which could be attributed to the substantial production of latent heat and moisture from the adjacent ocean
One consequence of these circulation patterns is that rainfall patterns in West Africa, where northern Nigeria is situated, show annual variation, and this fluctuation persists over a long period
Summary
Most studies have revealed that several drought episodes hit the northern part Nigeria and left the region in a pitiable socio-economic condition. The geographical environment of the tropics is endowed with some important features like high plateaus and equatorial rainforests which contribute their own quarter of heat that influenced the tropical circulation [5]. These produced heats vary with latitude and longitude and on both annual and, in oceans’ case, non-annual scales. One consequence of these circulation patterns is that rainfall patterns in West Africa, where northern Nigeria is situated, show annual variation, and this fluctuation persists over a long period. Studies have revealed that variations in West African rainfall patterns are tele-connected with distant locations phenomenon like El-Nino [6] [7]
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