Monitoring drought and effects on vegetation in Sokoto state, Nigeria using statistical and geospatial techniques

Abstract

This paper aimed at assessing drought occurrences and its effects on vegetation cover in Sokoto State, Nigeria using geospatial and statistical techniques. Monthly precipitation data which span through a period of 40 years (1980-2010) and 30 years (1982-2011) respectively were used for generating Standardized Precipitation Index (SPI) graphs and maps. LandSat   imageries of bands 3 and 4 acquired by Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) Sensor were used for generating Normalized Difference Vegetation Index (NDVI). SPI and NDVI were generated for the study area based on inter-annual and decadal timescale. Findings showed that SPI values varied from extremely dry condition to extreme wet condition although near normal condition ranked highest while extremely wet condition ranked least.  It also revealed that most of the Local Government Areas experienced near normal conditions but  Isa, Sabon Birni and little part of the boundary between Goronyo and Wurno experienced moderately wet conditions between 1982 and 1991. It was further observed that the whole region was dominated with near normal condition except Sabon Birni and Isa LGAs that experienced extremely, severely and moderately wet condition between 1992 and 2001. In contrast, the SPI values for over 90% of the state  between 2002 and 2011 fall within the severely dry conditions. Findings further showed that change scenarios observed from the derived NDVI and SPI maps indicated that the climatic variability currently being experienced is likely to increase and intensify in future. It is obvious that urgent attention on drought management over this region is needed.

Keywords: Drought, SPI, NDVI, Vegetation Cover, Landsat Imageries, Northern Nigeria