The sustainability of land and water managemet of the lower Seyhan irrigation project area under progressing climate change

The aim of this study is to determine the historical changes in land use, irrigation/drainage and salinity (soils and ground water) of the large scale Lower Seyhan Basin (LSB) irrigation area along with the probable future climate change senarios. The results obtained from field measurements, laboratory analysis and field questionnaires were interpreted by the use of various models leading to the projection of the climatic components sought to change by 2070.The crucial structural changes, concerning the crop patterns, the management of the irrigation water and the waring out of the irrigation facilities that have been initiated in the 1960's, are the primary drivers of the decreasing irrigation efficiency in the area. Thus, despite the existence of the continuous water use programming approach implemented in the project area, the lack of night irrigations expected to be followed by the farmers and the insufficient control of the water by the water use associations, are additionally responsible for the low irrigation efficiency (40%).Despite the occurrence of the annual fluctuations and the seasonal peaks of the past, a more or less uniform ground water level and a decrease in their salt contents has recently been determined in the study area. This has most probably being achieved by the increased water use and renovated drainage facilities as well as the longer irrigation periods practised in the basin in the last 20 years. The analysis carried out by the IMPAM model revealed the contribution of the water leached from the irrigation canals in alleviating the fluctuating highly saline ground water levels. Moreover, the effect of the land use was determined to be higher than the effect of the present impact of the climate change on the ground water movement. The leaching along with the evacuation of the excess salts was achieved by the increased use of irrigation water and the highly efficient drainage system respectively along the North-south relief of the basin towards the Mediterranean coast, where high salinity stil exists due to the lack of draining facilities.The projections revealed that the annual precipitation of the basin is estimated to decrease by 42 to 46 % mainly during the winter months. This decrease is foreseen to increase the irrigation requirement and cause a shift to a longer irrigation period from early spring to late autumn. The stable and high water table level of 150 cm of the present is estimated to fall by 2070 by the impact of the decreasing precipitation. Moreover , if an efficient drainage system is not constructed in the 4. stage irrigation area (the southernmost part of the delta which will shortly be included in the irrigation programme) the existing high water table can cause severe problems in this part of the basin. Consequently, the present and future potential land use programmes should highly consider, the income generating indigenous crop species with special care on halophytes while primarily aiming the rehabilitation of the degraded lands. This should be coupled with a complementary long-term ''Salinity risk'' monitoring programme with baseline information on soils and their surface and sub-surface topographies along the north-south transect of the downspring basinKey Words: Lower Seyhan Plain, Irrigation, Ground Water, Salinty, Climate Change