REMOTE SENSING OF THE IMPACT OF GROUNDWATER LOWERIN G ON AGRICULTURAL ACTIVITIES IN THE JEFFARA PLAIN, NORTH-WEST LIBYA

Groundwater is the main source of freshwater in Lib ya, providing a vital supplement to surface water s ources. Groundwater availability and quality are, however, vulnerable b oth to climate change and over-abstraction, and in regions where the water table has lowered there has been a consequent impact on a gricultural activities. This paper is part of an on going study that examines the impact of water table change on agricultural activi ties in NW Libya during the period 1988 to 2000. La ndsat TM data from 1988, 1992, 1996 and 2000 have been integrated with vario us thematic maps of the study area and with well/bo re-hole data to assess the nature and extent of change. A supervised Maximum Likelihood approach was used to classify each image into land cover classes that were deemed sensitive to change in groundwater levels. QuickBird (2002) and Spot 5 (2000) were use d to aid selection of the training sets and to test the accuracy of the class ified images, with resulting accuracies of over 80% obtained. Change in agricultural activities was readily apparent, especially the red uction in citrus and other fruit cultivation, which require abundant supplies of irrigation water, (64.6% reduction from 2000 compared to 1988). This was further demonstrated by a qu estionnaire survey distributed to farmers in the region. Results from t he questionnaire analysis have confirmed many of th e changes noted in the remote sensing results, as well as articulating the link b etween groundwater and changes in agricultural acti vity, helping to interpret the classes seen in a socio-economic context.