Fig. 4 Ratio of actual evapotranspiration (Et_a) to reference evapotranspiration (Et_r) as a function of date during the season for six of the eight sites (Sites 4 and 7 were close to 2 and 6, respectively). The lines were fit using the cubic spline smoothing interpolation feature (SM25) of PROC GPLOT (SAS Inst., 1990)