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ASCE/FAO PM -- Daily vs. Hourly <br />Timesteps -- Both are good <br />Davis, California <br />CIMIS Station <br />2008 – 2012 <br /> <br />Grass Reference <br />y = 1.005x + 0.182 <br />R² = 0.957 <br />0 <br />2 <br />4 <br />6 <br />8 <br />10 <br />12 <br />14 <br />16 <br />18 <br />20 <br />0 2 4 6 8 10 12 14 16 18 2024-h Timestep Ref. ET, mm d-1 Summed Hourly Reference ET, mm d-1 <br />Conclusion: You <br />can use hourly or <br />daily weather <br />data. Hourly <br />estimates may <br />be a “few <br />percent” more <br />accurate. <br />The FAO-56 hourly PM was applied using 50 s/m surface resistance <br />as recommended in Allen et al. 2005