Assessment of trends in crop type and land cover change using GIS in Yatta sub-county, Kenya

Assessment of the distribution and dynamics of vegetation using remote sensing techniques and Geographical Information Systems (GIS) have proven to be efficient tools in monitoring agricultural activities as they provide methods for analysis of land and planning purposes. It is therefore important to determine the crop type and land cover change in the semi-arid regions hence the current study was carried out to assess the changes in crop type and land cover using multi temporal Landsat satellite imageries from 1986 - 2012 in Yatta District, Kenya. The LANDSAT TM, ETM and ETM+ satellite images for the years 1986, 2000 and 2012 in Yatta Sub-county were classified using ENVI 4.7 under supervised classification into different crop types and land cover. False colour composite using different reflective indexes (Bands 4, 3, 2) were used for the visual examination and interpretation of the images and maximum likelihood method of classification used. The percentage changes of crop types and land cover between 1986 – 2000 and 2000 – 2012 were determined using ENVI EX by comparing two images of different times. Questionnaires were administered to establish change detection from traditional (crops grown in the past but have been abandoned and underutilized) to introduced (crops grown as a result of technological advancement and economical advantage) crops in specific locations within the respondents farms. More recently, in 2012, maize and beans covered 72% while traditional crops (Sorghum, finger millet, cassava, dolichos, sweet potatoes, green grams, cowpeas, pigeon pea, pumpkins), shrub land, bare land and riverine forest covered 14, 6, 3 and 5% of the study area, respectively. There was a significant (p=0.000) decline in the area under traditional crops (10.44 and 11.93 %), and a significant (p=0.000) increase in maize (4.70 and 22.73%), beans (23.83 and 2.6%) and bare land (3.42 and 1.03%) between the years 1986 – 2000 and 2000 – 2012 respectively. However, there was a significant (p=0.006) decrease in riverine vegetation (2.7 and 3.13 %) as well significant (P=0.000) decrease in shrub land (18.81 and 11.3 %) between the years 1986 – 2000 and 2000 – 2012 respectively. From the results, it is clear that there has been a tremendous change in the crop types and land cover within the last two decades in Yatta sub – County with a clear trend established in the shift in crop types from traditional crops that are more adaptable to the regions’ local climate to introduced crops that are preferred by the farmers due to their economic significance. This study is therefore likely to be used for future generations monitoring methods especially for crop type change as a result of traditional systems and land husbandry rapidly being abandoned. It will also inform government policies that will cater for the abandoned traditional crops and encourage their re-adoption especially in the ASALs where they are more adapted as compared to the modern crops.