Sensitivity of the Penman-Monteith reference evapotranspiration equation to meteorological variables for Puerto Rico

Spatiotemporal variations in reference evapotranspiration (ET_o) are sensitive to the meteorological data used in its estimation. The sensitivity of the ASCE standardized ET_o equation to meteorological variables from GOES-PRWEB dataset was evaluated for the island of Puerto Rico. Island wide, ET_o is most sensitive to daily mean relative humidity (RH_mean), followed by solar radiation, daily maximum (T_max) and minimum (T_min) air temperatures, and wind speed with average absolute relative sensitivity coefficients (SCs) of 0.98, 0.57, 0.50, 0.27, and 0.12, respectively. The derived SCs guided the prioritization of bias correction of meteorological data for ET_o estimation from two downscaled climate models (CNRM and CESM). The SCs were applied to evaluate how meteorological variables contribute to model errors and projected future changes in ET_o from 1985–2005 to 2040–2060 at irrigated farms in the south. Both models project a 5.6% average increase in annual ET_o due to projected increases in T_max and T_min and a decrease in RH_mean. Despite ET_o being most sensitive to relative changes in RH_mean, the contributions from RH_mean, T_max, and T_min to future changes in ET_o are similar. CESM projects increases in ET_o in March, November, and December, increasing the potential for crop water stress. Study limitations are discussed.