What causes the potential evapotransportation to vary from month to month?

Potential evapotranspiration (PET) varies from month to month primarily due to changes in temperature, sunlight, and humidity. Warmer temperatures increase the rate of evaporation and transpiration from plants, while longer daylight hours in certain months enhance photosynthesis and water loss. Seasonal variations in precipitation and soil moisture also influence PET, as drier conditions can lead to higher rates of evaporation. Additionally, atmospheric conditions such as wind speed can affect the rate of water loss throughout the year.