Study Evapotranspiration in Iraq Using the Penniman-Monteith Equation for the Period (2008-2020)

Evapotranspiration is considered an essential element for the stability of the ecosystem due to its importance in many aspects, including the water cycle, which is an important source of fresh water for humans, animals and plants. It also influences climate and temperatures and regulates weather. It also enters into the design of crop irrigation networks, knowing their water needs to prevent drought and desertification. The Penman-Monteith method is effective and accurate for calculating daily reference evapotranspiration and has been adopted by the Food and Agriculture Organization (FAO) as a standard method. This study aims to calculate the variation in evapotranspiration rates in Iraq using the Penman-Monteith method over the past thirteen years (2008-2020) in five equal periods (2008, 2011, 2014, 2017, and 2022). This study showed that the total rates of evapotranspiration are decreasing, and these values ​​peaked in 2008 and then decreased significantly in subsequent years. The reason for this decrease is the decrease in wind speed and the increase in relative humidity. It was found that evapotranspiration rates in the central and southern governorates are higher than in the northern governorates. However, there are deviations in the rates for some stations, such as in 2020, which witnessed a general decrease in evapotranspiration rates, except for some stations that recorded an increase. For example, Khanaqin station recorded the highest increase in evapotranspiration rates, which amounted to 23.6%. The reason for this increase is the increase in temperatures by 5.2% and the decrease in relative humidity by -6.5%.