In this study, the base flow estimation method was used to assess long‐term changes of groundwater recharge in Northern Taiwan. The Mann‐Kendall test was used to examine the characteristics of the trends. This was followed by trend slope calculation and change‐point analysis. The annual groundwater recharge was found to exhibit a significant upward trend for the Fushan and Hengxi stations (Tamsui river basin). On the other hand, the Ximen Bridge station (Lanyang river basin) recorded a significant downward trend. Calculations showed that the rate of change for the Fengshan and Touqian river basins was small (less than 10%). However, that for the following stations was greater than 30%: Fushan, Hengxi, Ximen Bridge, and Niudou (also in the Lanyang river basin). The results of the change‐point analysis further indicated a significant change‐point for the annual recharge at Fushan, Hengxi, and Ximen Bridge stations in 1999, 1983, and 2001, respectively. The findings can be used for regional hydrological studies and as reference for water resource planning.
Part of the book: Groundwater
A limited number of parameters or a single meteorological parameter was used in this study to estimate evapotranspiration. The main objectives of this study are as follows. (1) The Penman-Monteith method was used to estimate ET. The empirical formula published by the Food and Agriculture Organization (FAO) was applied via substitution to compare situations that were missing certain meteorological parameters. (2) Radiation-based methods and temperature-based methods were compared with the Penman-Monteith method to estimate ET and discuss their applicability in the study area. With Tainan Weather Station of Taiwan as the study area, this study selected the Penman-Monteith method as well as six other radiation-based estimation formulas: Makkink, Turc, Jensen-Haise, Priestley-Taylor, Doorenbos-Pruit, and Abtew methods. The other four temperature-based estimation formulas, namely, Thornthwaite, Blaney-Criddle, Hamon, and Linacre methods, were used to estimate ET and compare the differences and the results were compared with the Penman-Monteith method. The results showed that there was little effect on estimating ET using the Penman-Monteith method when the wind speed data was missing or insufficient. The Turc method was the best among the six radiation-based estimation formulas, while the Linacre method was the best temperature-based estimation formula. Generally speaking, radiation-based estimation formulas were more accurate than temperature-based estimation formulas.
Part of the book: Current Perspective to Predict Actual Evapotranspiration
In this study, the water balance concept is used to understand the relationship between discharge and storage in a basin. Three low flow analysis models developed by Brutsaert, Vogel and Kroll, and Kirchner are used to select recession curves that are parameterized using lower envelope, linear regression, and binning methods to characterize basin hydrological behavior. Furthermore, the lowest annual groundwater storage, which is analyzed according to trend, slope, and a change point test, is used to assess the long-term storage properties of southern Taiwan and is also quantified. The water balance concept is used to assess the impact of discharge on groundwater storage that is affected by the different low flow analysis models. This can lead to a more clear understanding of the relationship between groundwater storage and discharge. After statistical tests of trend, it was determined that Chaozhou Station, which has a significant decreasing trend of the lowest groundwater storage, should implement precautionary measures such as an underground reservoir, an artificial recharge, and a collection gallery in the Donggang River Basin.
Part of the book: Aquifers