Lack of long-term hydrological monitoring makes it difficult to determine impacts of changing land use on the water dynamics for many catchments in Africa. Here we use local ecological knowledge (LEK) to explore the impacts of rapid expansion of eucalyptus agroforestry on water security in the Ethiopian highlands. Local knowledge about the impacts of changes in tree cover was collected from farmers (n = 30), extension staff (n = 2) and timber merchants (n = 2) in five kebeles within the Jeldu woreda. Jeldu has undergone significant land use change over the last forty years. The area was heavily deforested 20 years ago and farmers associate this time with a major change in the water dynamics. Recently the development of a new road to Goja, the main town, opened up the area as a source of timber for Addis Ababa. This has resulted in a substantial expansion of eucalyptus plots adjacent to roads on the upper plateau and in riparian areas where growth is accelerated. Poorer farmers have been displaced on to the sloping land (which used to be woodland) where there is now evidence of rapid soil degradation. The key findings were that farmers identified significant trade-offs at the plot scale between eucalyptus and adjacent crop fields. They also identified indicators suggesting the sudden increase in eucalyptus cover had accelerated declines in water availability at landscape scales. The study showed the value of using LEK for exploring immediate landscape scale dynamics in the absence of hydrological monitoring. Whilst there is a degree of uncertainty surrounding the impacts of eucalyptus, this research demonstrated local awareness associated of problems associated with unregulated expansion of eucalyptus woodlots on the water regulating capacity at immediate landscape scales in the Ethiopian highlands
