Evaluation of Evaporation and Runoff in the Goksu Basin according to the Methods of PENMAN and THORNTHWAITE

Abstract

It is not possible to survive without water for particularly human-being and the other creatures. Especially in recent years, the demand for water has increased exponentially with the increasing use of water such as drinking, irrigation, industry and energy production due to the rapid increase in the human population and the increasing demand for natural resources. It is important to examine and evaluate the stream basins, which are vital for water resources both in the world and in our country, in terms of water potential. Therefore, Göksu Basin, which is an important sub-basin of the Seyhan Basin, which has a significant water potential in our country, is also very important in terms of water potential. In this study; evaporation and runoff are important parameters to reveal the water potential of Göksu Basin. PENMAN and THORNTHWAITE methods, which are commonly used in the world and in our country as well as, are used in the calculation of these parameters in the research area. The data obtained from these methods are correlated with the current height parameter produced from the data of Current Observation Station 1805 located in the river mouth of the basin. While the average annual temperature of the basin is 12.8 C◦, the annual total precipitation is 860.3 mm. According to calculation made in accordance with the Penman method, the corrected PE (Potential Evapotranspiration) is 597.1 mm while the actual evaporation (ET) is calculated as 437.2 mm. Accordingly, the total runoff in the basin is calculated as 423.3 mm. (table-4) According to the Thornthwaite method, corrected PE (Potential Evapotranspiration) is 620.9 mm while the actual evaporation (ET) is calculated as 304.2 mm. According to this calculation, the runoff is 535.7 mm. It is seen that the current height is 429.2 mm, in the calculation made on the natural currents obtained from the Current Observation Station (COS) 1805 located in the river mouth of the study area. (table 4) In other words, it is the amount of water passing into the runoff in the basin. When the annual average runoff values obtained by the application of both methods are correlated with the current height; Penman has an average of 0.98 while Thornthwaite has an average of 1.24. When the results of the implementation of both methods are compared; In addition to the parameters such as lithology, vegetation, morphological structure and the temporal course of precipitation vary; In comparison with Thornthwaite method, Penman method has been found to be quite successful with a ratio of 0.98. On the other hand, it has been found the accuracy of Thornthwaite method with a ratio of 1.24 has been stayed in background with respect to Penman. In the annual average precipitation and current height correlations, the annual average actual evaporation (ET), Penman is 1.01, while Thornthwaite is 0.70, so it has been found that Penman method has a much better performance also in the evaporation likewise the runoff. In addition, when the parameters of Penman and Thornthwaite methods used for the calculation of evaporation and runoff in Göksu Basin scale have been compared; It is possible to say that the parameters of the Penman method are more rational than Thornthwaite. The fact that the Penman method has been accepted as a reference method in research on climate and hydrological processes around the world also confirms processes in question.

Key words: Göksu Basin, Thornthwaite, Penman Method, Water Balance Sheet, Evaporation