Possible effects of climate change on evaporation

In recent years, the most popular topics related to environment are climate change and water problem. In particular, the effects of climate change in the future on water resources are the most critical issues on the agenda. As of its consequences, climate change has affected many sectors directly or indirectly. Therefore, the impacts of climate change has been felt in the last 50 years in the world. Its effects have been discussed by wide range groups such as civil society organizations, enviromental groups, politicians and businessman and among the environmental issues which have taken place on the top. One of the biggest challenges of climate change is the impact on water resources in the future. In this context, determining the possible impacts of climate change on water resources and planning of adaptation strategies are required for the future. To achieve this goal, the possible effects of climate change scenarios on water resources (inputs and ouputs) must be determined taking into account of different climate change scenarios. Evapotranspiration is one of the important components of hydrological cycle. For this reason, having knowledge about of the water losses by evaporation and transpiration (evapotranspiration) is significant for the management and planning of water resources especially in arid and semiarid countries. In particular, management and planning of water in our country have an essential role. Water is extremely important for our country's economy and agriculture because 70-75 % of the available water is used for agricultural purposes. In order to manage and plan water resources as sustainable manner, the net inputs and losses in terms of water balance would be occurred in the future, must be determined. In this context, the status of the evapotranspiration from past to present in three cities located in the Thrace Region (Edirne, Kırklareli, Tekirdağ) was investigated in this study. Additionally, the regional climate model data obtained in the framework of the A1B climate change scenario, the tendency of evapotranspiration is estimated until 2040. In this study, the data, between 1975 and 2010, modeled and measured at the meteorological obsorvetation stations, which located in Edirne (41° 40' N latitude 26° 33'E longitude), Kırklareli (41° 44' N latitude 27° 13' E longitude) and Tekirdağ (40° 59' N latitude 27° 29' E longitude) were used as past dataset. In addition this, the model outputs for a period of 2015 and 2040 were used in order to investigate the impacts of possible climate change on evapotranspiratişon. In the scope of the study, evaporations (evapotranspiration) were calculated by 20 different methods which are commonly used methods in the world. Calculations of evapotranspiration by these methods can be performed with available data (temperature, radiation, wind and relative humidity). The study was conducted primarily for the analysis and evaluation of data . In this context scatter plots and time series were drawn for 1975-2010 model and 1975-2010 station (measured) data. The relationships between datasets were presented. It has been estimated statistically important relationships with high determination coefficients between modelled and measured data for the meteorological variables; temperature and global solar radiation. The weak relations and determination coefficients for wind speed and relative humidity were obtained between modelled and actual data. Moreover, within the scope of data analysis, long-term average of data has been mapped for the Thrace region on monthly basis. After the data analysis, the tendency of evapotranspiration from the past to present (1975-2010) and from the present to the future (2015-2040) were analyzed and compared. In this context, firsly, time series of the evopotranspiration calculated by using modelled and station (actual) data for the 1975-2010 period and modelled data for 2015-2040 period were drawn. It has been determined for both periods that there is a slight increase trend for evapotranspiration. The problem encountered during the study is the lack of information of proper methods from many methods for our country arising from lack of supporting studies which are performed by field measurement. This is a lack for the usage of evapotranspiration equations by engineers. For this reason, it should be estimated which equation is suitable for our conditions in order to estimate evapotranspiration. Thus, it is clear need to measure directly the evapotranspiration by field experiments and methods. Therefore, the methods were compared with Penman-Monteith method (reference method). The variance of 20 methods were examined according to Penman-Monteith method which is one of the 20 methods and recommended as a standard method by FAO (Food and Agricultural Organization). As a result of comparison, for all stations and for both past and future situations, the best results were obtained by McGuinness and Bordne (1972), Hargreaves (1975) and Jensen Haise (1963) methods, the worst result were obtained by Turc (1961) method. In order to compare the difference between Penman Monteih and other methods, (Root Mean Square Error (RMSE) and Mean Bias Error (MBE) were calculated. According to the error calculation that is based on Penman Monteith method, Hargreaves and Samani (1985) and WMO (1966) methods gave the lowest error value, and Turc (1961) method gave the highest error value. After the comparison of methods, annual averages of monthly total evapotranspiration were compared as model and station (actual) data for both periods. In addition to the climate change scenario results, in order to determine sensitivities of evaporanspiration equations against temperature and global solar radiation, hypothetical scenarios are derived, too. In the scope of hypothetical scenarios, the daily average temperature was increased 3°C and 5°C and the daily average global solar radiation was increased 1, 2 and 3 MJ m-2. After this operation, time series of evapotranspirations for both periods were obtained in the scope of these hypothetical scenarios and scenarios compared with each other. As a result of comparison, it has been determined that evapotranspiration values which are calculated by using data for a period of 2015-2040 model data and calculated by sensitivity analyzes in which temperature was increased 5°C and global radiation was increased 3 MJ m-2 day-1 gave the highest result as annual average of monthly total evapotranspiration. Additionally, the methods used in this study were compared between each other as reference and potential evapotranspiration. As a result of comparisons, it is determined that Albrecht (1950) and Brockamp and Wenner (1963) methods produced the highest evaoptranspiration values, while Turc (1961) method presented the lowest values as potential evapotranspiration and de Bruin (1979) and Schendel (1967) methods gave the highest reference evapotranspiration values, whereas Irmak (2003b) method produced the lowest values. In order to reveal tendency of evapotranspiration, deviations of annual total evapotranspiration from the long-term average of annual total evapotranspiration were examined. In this context, an increasing trend of evaporanspiration was determined. In this study, evapotranspirations were calculated by considering actual measurements at the stations and regional climate models results. Morever, hypotetical senarios for future periods have been also analyzed and taken into account. The results indicated that, the calculated average evapotranspiration using twenty equations is expected to increase up to 15% in the future.