This book provides the most recent method for calculating evaporation-let reference and evaporation-let crop of climatic data and transactions crops, this book contains three sections ramifications of which eleven chapters, including Introduction to let evaporation, FAO / Penman - Monteith, climatic data, presented at Vaporize let crop, the crop coefficient method unilateral, bilateral factor crop evapo-let the crop under stress conditions of soil water.