Spatial and temporal change of reference crop evapotranspiration in Marmara Region

In recent years, global warming and climate change, rapid population growth, industrialization and ensuring sustainable food production have made it necessary to use water resources effectively. The biggest water user is agriculture. Reference crop evapotranspiration (ETo) has an important role in agricultural water management, irrigation projects and preparation of irrigation schedules. In this study, the annual total ETo values were estimated using the FAO Penman-Monteith method for 18 meteorological stations in the Marmara Region between the years 1990-2020 and their spatial and temporal changes were evaluated. For this purpose, annual total ETo trends were determined for each station using the non-parametric Mann-Kendall test and Sen method, and ETo maps were prepared using the Geographical Information System (GIS) Inverse Distance Weighted (IDW) interpolation method. According to the results of this study, the annual total ETo values varied between 742.3-1440,7 mm. According to the ETo trend analysis, statistically significant increasing trends were determined for Edirne, Kocaeli, Sakarya, Bozcaada, Çanakkale, Kırklareli, Uzunköprü, Tekirdağ, İpsala and Dursunbey stations, while the trends were significantly decreasing for Kumköy-Kilyos and Keles stations. However, the increasing trends in ETo for Bandırma, Bursa, Şile, Florya and Gönen stations and the decreasing trend determined for Bilecik were not statistically significant. When the annual average ETo map is evaluated, it is seen that ETo has reached high values in the western parts of the Marmara Region (south of Edirne, west of Balıkesir and Çanakkale), while in the northern parts of the region, east of Kırklareli and Tekirdağ, and in the eastern parts of the region, east of Istanbul, Kocaeli and Sakarya, ETo values decreased. In addition, while the annual average ETo values were found to be low in Kırlareli, the east of Tekirdağ, Kocaeli and Sakarya, statistically significant increasing trends were determined in the annual total ETo values calculated from the data of meteorology stations in these provinces.