Capacity of irrigation networks is vital to satisfy peak crop´s water demands and to improve resource use efficiency. The methods to size canal capacity depend on mainly two variables: one agronomic - crop evapotranspiration - and the other hydraulic –system´s global efficiency. However, there is not an integral procedure to estimate the agronomic variable in large irrigation areas with a diversified crop pattern, different planting dates, and several crop seasons. In this paper, a methodology is presented to estimate the integrated evapotranspiration for large irrigation areas that is used to estimate irrigation canal capacity in conjunction with the global efficiency variable. This methodology was applied to the “Santa Rosa” Water Irrigation Association in the 075 Irrigation District located in the state of Sinaloa, Mexico. With the proposed methodology, a value of 4.08 mm·dia-1 was estimated for the integrated evapotranspiration at Water Irrigation Association level. Using a design global efficiency of 49 %, the canal capacity was calculated to be 21.70 m³·seg-1. Considering estimated design discharge and efficiencies used, the results are comprehensive giving flexibility for water distribution. It is concluded that the proposed methodology fulfills its established objective and can be applicable to other cases.

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