Geology Reference
In-Depth Information
PM ET
0
values are higher than FAO56
PM ET
0
by 30 % for the peak month
(August) during the study period year 1995. This was because of over-predicted
hourly CIMIS-ET
0
values in that month. The
-
figure also showed the variation of the
monthly pan coef
cient in relation to the ET
0
estimated using different models. The
higher pan coef
cient is observed corresponding to the CIMIS-PM ET
0
. From
Fig.
7.15
we can note that, in comparison with FAO56
PM, the Copais method
slightly underestimates in the early months of study duration at the Brue catchment.
The values of overestimation were in a 2
-
8 % range in the early months for the
-
CIMIS PM method, compared to FAO56
PM, on
a monthly basis, ASCE-PM showed quite similar trends at the Brue catchment.
The monthly ET
0
variation of different methods at the Santa Monica station in
2002 is shown in Fig.
7.16
. From the
PM. In comparison with FAO56
-
-
figure, we can note that other empirical
methods underestimate in comparison with the FAO56-PM method in almost all
months except dry months such as May, June, and July. The ANN model over-
estimates the FAO56 model in the month (July). In general, the ANN model gave
better monthly estimates than Copais and CIMIS ET
0
in the Santa Monica Station.
Figure
7.17
shows the comparisons of annual ET
0
estimations for the year 1995 at
the Brue catchment and that of the Santa Monica station for the year 2002.
Although the trends of the estimated ET
0
with the Copais method were closer in
hourly time steps, the daily time step equation did not exhibit the same results. In
the present calculations, the annual sum of ET
0
estimations based on the CIMIS-PM
showed the highest value among the tested methods, having the value
617.7 mm year
−
1
in 1995 at the Brue catchment. The ET
0
estimations by the Copais
approach have the lowest value of 362.7 mm year
−
1
, whereas the ASCE-PM
method was very close to the FAO56-PM having the value 608.9 mm year
−
1
in
1995. Similar results were found in the ANN model with an annual value of
Fig. 7.16 Monthly variations of different reference evapotranspiration methods and ANN results
at Santa Monica station during 2002
