| The government of Turkey is implementing a large water and agricultural development scheme known as the Southeastern Anatolia Project in the semi-arid upper Euphrates - Tigris Basin. As part of this development, 215,000 hectares have been irrigated over the last two decades. The project aims to provide an irrigation network serving 1.5 million hectares when fully completed in 2015. Transformation of this magnitude from dry agriculture to irrigation is known to affect the temperature and humidity profiles of the atmosphere, wind velocities, and local precipitation. What is less known is the influence of irrigation on hydrologic fluxes such as evapotranspiration. To study these effects this research combines satellite remote sensing with analyses of long-term meteorological observations, evaporation models that account for changing soil moisture, and climate simulations.; Analysis of remote sensing and local meteorological data indicate that both the irrigated areas and water usage by irrigation increased by over 2000 percent between 1980 and 2001. The results also indicate that high temporal frequency remotely sensed observations are useful in local land use studies for the purpose of selecting appropriately timed high resolution observations.; The transformation of the Harran Plain to irrigated agriculture provides an ideal experiment for testing the Complementary Relationship between potential and actual evapotranspiration. As predicted by the Complementary Relationship, potential evapotranspiration has decreased. However, decreases in wind speed, as opposed to a large increase in humidity, are the main cause of this decline. The relationship between actual and potential evapotranspiration compares well with estimates based on water balance and simulations. Wind speed and humidity data are consistent between model and observations after performing Monin-Obukhov scaling of observation heights.; This research demonstrates the existence and quantifies the magnitude of scale-dependence in the relationship between irrigated area and the amount of water required per unit area. Assuming that the changes in future evaporation conditions will be similar to the Harran Plain, water use for irrigation is expected to decrease over 50 percent in future irrigation sites. Incorporating this decrease in overall planning of future irrigation projects will lead to significant water savings and improve sustainability of water resources. |
