Developing mathematical models to calculate annual evapotranspiration rates in Iraq using climate data.

Abstract Evapotranspiration is considered the fuel that controls the water cycle in the natural world. It is necessary for the stability of ecosystems and is involved in many important aspects in calculating groundwater quantities, determining optimal locations for building dams and reservoirs and knowing the water needs of crops. The work is divided into two main parts. The first includes the use of The Penman-Monteith method, which is considered the most standard method in the world according to the Food and Agriculture Organization (FAO), for calculating the annual rate of evapotranspiration in Iraq for the past fifteen years (2008-2022). The second part is a modification of a simple method for calculating evapotranspiration, which is the Thornthwaite method, to give results close to the accuracy of the Penman-Monteith method, as the modification was made using different statistical methods. The study showed the possibility of using the modified Thornthwaite method as an alternative to the Penman-Monteith method to calculate evapotranspiration in all regions of Iraq.