Agriculture Reference
In-Depth Information
very significant reduction considering that the average pan evaporation
in 2002 was only 103.9 mm per month in Lajas. It will be interesting
to see whether this trend continues in the future or whether it begins
to level off.
• The decreasing pan evaporation observed at Lajas and Río Piedras is
consistent with the observed decreasing trend globally.
• Pan evaporation at two sites (Adjuntas and Gurabo) increased. These
results are contrary to the observed global decrease in pan evapora-
tion. Both sites are located in humid areas. It is interesting to note that
Adjuntas is at a relatively high elevation (549 m), whereas Gurabo is
at a relatively low elevation (48 m).
Figure 6 shows the estimated long-term average monthly reference ET
for each substation. As with pan evaporation (Fig. 2), Fortuna shows the high-
est ET
o
, and Adjuntas shows the lowest values during most of the year. How-
ever, ET
o
for Lajas was essentially identical to that of Fortuna, whereas the
Lajas pan evaporation (Fig. 2) was lower than that of Fortuna. There are two
possible explanations for this:
FIGURE 6
Long-term average monthly reference ET for the seven substations.
1. The local environment may have gradually changed in the vicinity
of the evaporation tank in Lajas. For example, installation of new
structures, establishment of trees, or relocation of the evaporation
tank. Development of the Lajas Valley may also have influenced a
change in pan evaporation at the substation.
2. Pan evaporation and reference ET may not be directly comparable.
Allen et al. [10] list the following factors that may cause significant
differences in loss of water from a water surface and from a cropped
surface:
Search WWH ::
Custom Search