Fig. 4. (a) Six-day composite of system (soil + canopy) potential evapotranspiration (ET) ratio estimates from the ALEXI model at 5-km resolution, ending 1 July 2002. The nominal time associated with this image is 1.5 h before local noon, the time of the second GOES image used to compute surface radiometric temperature change. (b) Six-day accumulated precipitation, based on the National Centers for Environmental Prediction (NCEP) daily precipitation analysis product. (c) Canopy potential ET ratio. (d) Soil potential ET ratio.