Digital Climatic Atlas of Texas - Texas Water Development Board

interpolation of the missing value at the target station. Although this limits the number of
target stations that can be used, it is necessary to maintain the integrity of the
interpolation. While no interpolation can recover the data that does not exist, research
shows that using less than ten years often produces erroneous interpolations (Figure 5).
From Figure 5, for all climatic parameters using less than 10 years of training data
increased the mean absolute error of interpolation, however increasing it beyond 10 years
did not considerably reduce the error. Further, the test runs also showed that limiting the
search for stations with four highest monthly weights from among the 20 closest
benchmark station to the target station did not increase the interpolation error
considerably (Figure 6).
Another important finding from this test run is that lower standard errors were
obtained by using more than one month to create the monthly weights. For example,
using both September and October data as opposed to using only the October data to
calculate the October monthly weights produced a more accurate result (lower standard
error). Table 2 shows the combinations of months that produced the lowest standard
error, based on tests using one, two, and three months of data. Separate evaluations were
made for East and West Texas to calculate the monthly weights for precipitation and
temperature. Only for May and August in West Texas is a single month of data optimal
for calculating the monthly weight.
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