Optimum summer index and average potential water deficit.
Optimum summer index is based on the formula I= 10TX + 20S-7R where TX is mean daily temperature (°F), S is mean daily sunshine (h) and R is total rainfall (in.) during June, July and Aug. The index was found to be closely correlated with potential water deficit, which could be estimated using the formula d = ((I/100)-5)2. R.B.