Sensitivity Coefficients of Reference Evapotranspiration to Weather Variables across Turkey

Evapotranspiration (ET) is a key component of the hydrological cycle which is important for an assessment of water resources, drought, and irrigation management. Therefore, it is crucial to accurately determine ET. Reference ET can be calculated from meteorological data collected at weather stations. However, inaccuracies or uncertainties of sensor measurements may result in large uncertainties or errors in calculated reference ET. We performed sensitivity analysis of input weather variables (air temperature, wind speed, solar radiation, and relative humidity) to determine the relative effects of measurement errors on the accuracy of calculated grass (ET_os) and alfalfa (ET_rs) reference ET. Daily weather data from 1984 to 2018 from seven weather stations across Turkey were used to determine sensitivity coefficients for each of the weather variables. Comparison of the sensitivity coefficients, based on preliminary results, indicated that reference ET was the most sensitive to wind speed followed by air temperature across Turkey. We will further compare sensitivity coefficients to each weather variable across seven regions of Turkey to determine whether maintenance protocol can be uniform or different for weather stations in different regions of Turkey.