Evapotranspiration, water productivity and crop coefficients for irrigated sunflower in the U.S. Southern High Plains

•Sprinkler irrigated sunflower yield and water productivity are reported.•Sunflower was grown in a semiarid climate including a record drought.•Yield and water productivity were stable across drought and more normal conditions.•FAO56 adjusted crop coefficients (Kc) matched the data; with different crop calendar.•Comparison of reference ET formulations showed little chance of Kc conversion.