## 3 Results and Discussion
### Trends in Human Water Use  
For the study region, USGS statistics [38] indicate that the total water withdrawal for human use is about 140,471 million gallons per day in 2005 (Table 3). It also indicates that water withdrawal amounts vary by water use category, with thermoelectric power using the highest amount followed by public supply, industrial use, and irrigation. However, not all of these amounts are consumptive water. Consumptive water is defined as the water removed from available supplies without return to a water resource system. For example, the water used in manufacturing, or for food preparation that is not returned to a stream is considered consumptive. Human activities have different rates of consumptive water. For example, although a large amount of water is withdrawn for use in thermoelectric power generation, only 2.5% of it is consumptive [45]. Table 3 shows the different rates of consumptive water [46] for the different water use categories listed for our study area. Using these rates and the water withdrawal amounts provided by the USGS, we estimate that from the total human water use, about 4.67 mm, or 10.4% was consumptive water in the study region in 2005 (Table 3). This value is in good agreement with the USGS study in [47], which shows a 10% consumptive water rate as an upper limit for the study area in 1983.It is to be noted that in the study area, irrigated lands constitute only a small fraction of total land use [24], yet this land use type constitutes the second most amount of consumptive water use among the categories defined in Table 3.  
If we apply the 2005 consumptive water amount to the entire 108-year period of analysis, the total amount of consumptive water over the study area and over time would be 0.51 m in depth. Applying the 2005 consumptive water rate to all years is an overestimation since consumption rates were presumably smaller in the earlier years of the studied time period, when the population was smaller. Furthermore, following this logic, the underestimated period (2006-2008), with presumably higher population, is very short compared to the overestimated period (1901-2005). Finally, taking the overestimated storage amount into account, in addition to the overestimated consumptive water amount, there will still be 0.50 m of excess water unaccounted for (Table 4). In the eastern US, measured ET using lysimeters has been shown to reach roughly 0.83 m\(\cdot\)yr\({}^{-1}\)[48]. Using this value as a baseline of annual ET rate over the study area, to remove 0.50 m of excess water over 108 years (\(4.63\times 10^{-3}\) m\(\cdot\)yr\({}^{-1}\)), we estimate ET must have increased with an annual average rate of 0.56%, obtained by dividing the \(4.63\times 10^{-3}\) m\(\cdot\)yr\({}^{-1}\) by the baseline, over the study period. While we do not consider this an exact value of an ET rate of change, it is an estimated value that indicates ET has increased during our period of analysis, even given large overestimations of water storage and consumption changes. \begin{table}
\begin{tabular}{c c c c} \hline \hline (P-Ru) Accumulation & Storage & Consumptive Water & Residual \\ \hline
3.18 & 2.17 & 0.51 & 0.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Components of the hydrological cycle (m) over the period of analysis. Storage represents the total of the estimated maximum surface water (0.24 m) and groundwater (1.93 m) storage terms. The storage and consumptive water amounts are deliberate overestimates, contributing to an underestimate of the excess water that accumulated during the period of study. See text for details.