ESTIMATION OF PAN EVAPORATION COEFFICIENTS - Management, Performance, and Applications of Micro Irrigation Systems - page 112

TABLE 2 Results of a Student t-test comparing monthly pan coefficients based on pan
evaporation data from 1960 (approximate) to 1980 and 1981 to 2000.

t-Test Analysis Results
Confidence Level = 0.95 (Two Tail Test)
1960 to 1981 vs. 1981 to 2000:

1960 to 1981 1981 to 2000

Sample Size 84 84

Number of Missing 0 0

Minimum 0.5694 0.6732

Maximum 1.1579 1.2473

Standard Deviation 0.1398 0.1319

Standard Error 0.0153 0.0144

Coeff of Variation 18.5924 14.5441

Mean 0.7520 0.9067 Difference = 0.1547

Variance 0.0196 0.0174 Ratio = 1.1242

Paired t-Value

9.5097

Probability
6.24516E-015

DF Critical t-Value

83 1.9890

Co-Variance = 0.0074, Std Deviation= 0.0163

TABLE 3 Long-term average reference ET (ET o ) in mm/month for the seven
experimental substations.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Adjun-
tas

93 100 128 132 136 138 146 139 124 112 92 84

Coro-
zal

76 80 110 115 128 127 129 127 112 101 78 70

For-
tuna

104 107 139 147 157 156 166 159 141 124 100 96

Gurabo 87 93 121 128 133 131 135 132 117 105 85 80

Isabela 94 100 132 141 146 141 145 144 129 118 95 88

Lajas 97 102 138 145 162 162 164 157 137 120 95 87

Río
Pie-
dras

93 98 130 138 145 143 146 142 127 116 93 86

Aver-
age

93 100 128 132 136 138 146 139 124 112 92 84