Spatiotemporal drought assessment using vegetation health index and standardized precipitation index over Sudano-Sahelian region of Nigeria

Drought events were assessed using remote sensing index (Vegetation Health Index, VHI) and meteorological index (12-month Standardized Precipitation Index, SPI-12) over the Sudano-Sahelian Region of Nigeria (SSRN) between 2000 and 2010. Rainfall data of the SSRN were acquired from nine stations of the Nigerian Meteorological Agency (NIMET). Monthly Vegetation Index (MOD13A3) and 8-day Land Surface Temperature (MOD11A2) of the Moderate-Resolution Imaging Spectroradiometer (MODIS) were retrieved from the NASA's Land Data Product and Services Center (LPDAAC) website. The result from VHI evaluation revealed that about 121.926 km(2) and 36.063 km(2) of the region experienced extreme drought in the years 2003 and 2010, respectively, while SPI-12 detected no extreme drought condition during the same period. Both indices detected severe, moderate, and mild droughts (mild drought dominated the SPI-12 results) occurrences. The total area of the region under the influence of drought events from lowest to highest spanned from 233,259.276 km(2) (in 2007) to 279,189.364 km(2) (in 2002) and 2704.82 km(2) (in 2010) to 236,082.70 km(2) (in 2008) for VHI and SPI, respectively. Results from this study revealed that the VHI gave a better representation of drought severity with continuous/consistent spatial values compared to the SPI.