Significance of soil moisture on vegetation greenness in the African Sahel from 1982 to 2008

Abstract: Popular science The Sahel is a semi-arid eco-climatic transition zone in northern Africa separating the Sahara desert from the Africa’s tropical forest. The Sahel word in Arabic language means “shore” which is linguistically describes the appearances of vegetation as a shoreline defining the boundary of the Sahara desert. Soil moisture (rainwater accumulated over a period of time in soil) is considered one of the most important factors on vegetation growth in Sahel as the agriculture droughts occurs due to soil moisture deficiency. The projected number of Africans in semi-arid locations will suffer from increasing water stress by 2020s is between 75-250 million and this number is projected to increase to be between 350-600 million by 2050s. This study aims to evaluate the relationship between soil moisture and vegetation growth in Sahel region during 1982-2008 at different time lags. Land cover and soil texture data were used to investigate whether the relationship between soil moisture and vegetation growth are related to land cover and soil type or not. Satellite remote sensing data (vegetation index), modelled soil moisture data land cover map and soil type map were mainly used to achieve the purpose of this study. The most important findings of this study is the best correlations between vegetation greenness and soil moisture occurred at lag0 (no time lag differences), lag1 (one month time lag) and lag2 (two months’ time lags). The correlation relationship varied between low and moderate values in Sahel region indicating that soil moisture variable is not only the main driver for vegetation dynamics in the study area and maybe other factors such as human impacts could have a great contribution on vegetation changes in Sahel. Croplands and Grasslands are the main land cover types that increasing the correlation relationship between soil moisture and vegetation growth, whereas Entisols (occur in flood plains and steep slopes) and Alfisols (occur under forest and mixed vegetation cover) are the main soil types showing a positive effect on the correlation relationship between soil moisture and vegetation dynamics. Finally, good understanding the temporal relationship between water availability and vegetation dynamics can help us to know water affects plant growth and to predict the future relationship within a season between vegetation growth and soil moisture which can be used for detecting famine possibilities.