The Economic Value of Water and Ecosystem Preservation

4.4.2. Production Function Approach - Data
Data was also gathered from the USGS for inflows at Tivoli on the
Guadalupe River which is below the confluence of the San Antonio and
Guadalupe River, for the year 2000 - 2006. Rainfall data was also gathered as
days of precipitation per month for the Aransas Wildlife Refuge. Finally, the main
winter tourist season is from around December through February, while the
greatest number of tourists is during the summer months (Morehead, Beyer et
al., 2007). Tourist inflows are also influenced by bird migrations, in particular, the
winter nesting of the whooping cranes which occurs from October to April.
Dummy variables were constructed to account for tourist seasons and the
Whooping Crane nesting period.
4.4.3. Production Function Approach – Analysis and Results
The production function model was constructed based on various factors
discussed previously. The output was designated as the monthly number of
visitors to the Aransas Wildlife Refuge. The main input was average monthly
inflows to San Antonio Bay as measured the Tivoli Station on the Guadalupe
River. Other included factors attempted to account for correlation including
nesting times for the whooping crane, rainfall, peak period for winter Texans, and
summer holidays.
As discussed earlier, an analysis was conducted to look at correlation
between inflow data and visitor numbers. The strongest correlations were found
for same month inflows (positive), flows lagged by 6 months (negative) and flows
lagged 18 months (negative). Figure 4-4 below illustrates the monthly average
flows (2000-2006) as reported at the Tivoli gauging station compared to the
average number of visitors to the AWR (2001-2007). The low flow period
matches with the lower visitor numbers, which may be simply be a coincidence in
the data caused by the 6 month intervals between low and high flows. There are
spikes in the visitor data for March from an up-tick in boat tours and also in
October from bow hunters.
An eco-tourism production function was specified as the monthly number of
visitors to the Aransas National Wildlife Refuge as a function of several variables.
The independent variables included:
• “Flow_Tiv” - The monthly average flow as measured at the Tivoli
gauging station;
• “AWR_Precip - The total monthly precipitation at the Aransas National
Wildlife Refuge;
• “Holiday”- Dummy variable for summer holiday period (June-August);
• “Nesting” - Dummy variable for whooping Crane winter nesting
(October-April); and,
• “ Winter_TX” - Dummy variable for peak Winter Texans (December-
February)
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