Spatial and temporal analysis of recent drought using vegetation temperature condition index: case of Somali regional state of Ethiopia

Dissertation submitted in partial fulfillment of the requirements for the Degree of Master of Science in Geospatial Technologies.

The semiarid and arid areas of the eastern part of Ethiopia have suffered a series of droughts and famines in the years 1999/2000, 2003/2004, 2007 and 2011. Absence/decline of rainfall in two of the rainy seasons locally called Dihra and Gu as being the major fact behind drought. Besides, lack of appropriate monitoring techniques aggravate the situation of drought in the study area. In a region where the numbers of meteorological stations are not sufficient enough to monitor the onset and extent of drought, remotely sensed data presents fast and economical way of information as the ground condition reflects the overall condition of rainfall and soil moisture. In this study, the drought monitoring approach is developed using Terra-MODIS Normalized Difference Vegetation index (NDVI) and Land surface Temperature (LST) level-3 products. The approach integrates the land surface reflectance and thermal properties as well as the NDVI changes to identify the extent and pattern of the past drought years. From the NDVI versus LST scatter plot, we extract Vegetation Temperature condition index (VTCI) to map the variability and trend of the drought years. The year 2003 was found to be the driest year (more than 90% of the region affected by drought) and the season that showed increasing intensity of drought being Dihra. The correlation (r > 0.7) between rainfall and VTCI across the major meteorological stations suggested that the index could be used as good indicator of drought as rainfall does. The overall trend of drought condition for selected drought years suggested that eastern and southern regions will experience more severe drought in the coming year. Moreover, VTCI value for October from 2000-2011 showed similar increase intensity of drought condition. In addition, it was observed that sparse vegetation and shrub land are highly variable and bare soil region is consistently dry. Wetter regions were found in the area where the elevation is above 1500m above sea level.