VEGETATION RESPONSE TO DROUGHT IN SUDANO-SAHELIAN PART OF NORTHERN NIGERIA

Abstract

This study evaluated the vegetation response to drought over the Sudano-Sahelian zone part of Nigeria and the specific objectives are to assess drought occurrence, map the vegetation response to this occurrence, investigate the spatio-temporal land cover change and develop drought spatial pattern maps for the study area. Monthly mean Rainfall data for the period of 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 obtained from United States Geological Surveys Archive 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 (DSPM) for each selected modeled years. The vegetation response indicators used are land cover maps and Greenness Index (GI) maps. The results of SPI analysis revealed that many years of drought episode was recorded over the study area in the 1970s and 1980s but later reversed in the 90s towards the 21st century as the result show there was drastic reduction in the occurrence which indicate improvement in rainfall. On the other hand, the vegetation response analysis also depicted that the year 1986 was a dry year over the study area as the spatial extent cover by the vegetation was much less compared to the bare surface. But in the 1990s, greenness has returned to the areas that were previously bare soil, an indication of improvement in rainfall amount over the area. The study therefore concluded that there exists a kind of inverse relationship between drought intensity and vegetation growth and time lag in their response to dry or wet condition.