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

摘要

Groundwater is the main source of freshwater in Libya, providing a vital supplement to surface water sources. Groundwater availability and quality are, however, vulnerable both to climate change and over-abstraction, and in regions where the water table has lowered there has been a consequent impact on agricultural activities. This paper is part of an ongoing study that examines the impact of water table change on agricultural activities in NW Libya during the period 1988 to 2000. Landsat TM data from 1988, 1992, 1996 and 2000 have been integrated with various thematic maps of the study area and with well/bore-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 used to aid selection of the training sets and to test the accuracy of the classified images, with resulting accuracies of over 80percent obtained. Change in agricultural activities was readily apparent, especially the reduction in citrus and other fruit cultivation, which require abundant supplies of irrigation water, (64.6percent reduction from 2000 compared to 1988). This was further demonstrated by a questionnaire survey distributed to farmers in the region. Results from the questionnaire analysis have confirmed many of the changes noted in the remote sensing results, as well as articulating the link between groundwater and changes in agricultural activity, helping to interpret the classes seen in a socio-economic context.