Estimation of design water requirement using FAO Penman–Monteith and optimal probability distribution function in South Korea

Estimation of the design water requirement (DWR) is a key part of design and operation of agricultural water resource systems. DWR is determined from frequency analysis of crop water requirement, and the reference return period has been 10 years in South Korea. This study aimed to propose a guideline for determining DWR using Food and Agriculture Organization (FAO) Penman–Monteith method and optimal probability distribution function (PDF). To find an optimal PDF, nine types of PDF were tested using the Kolmogorov–Smirnov (K–S) and Probability Plot Correlation Coefficient (PPCC) goodness-of-fit methods. From the test, the Generalized Logistic (GLO) was selected and DWRs were estimated using the chosen optimal PDF. To demonstrate the DWR differences among the PDFs, DWR and drought reference design year were compared for the three selected PDFs, GLO, Generalized Extreme Values (GEV) and Weibull (WBU). The results would effect on the design and operation of the agricultural water resources structures in terms of capacity and capability in South Korea.