Response of Water-Table Depth to Fallow Duration and Hydro-Meteorological Factors: A Case Study in the Sigang District of Tainan, Taiwan.

The Chia-nan Plain is one of the major grain-growing areas in Taiwan where groundwater over-exploitation for irrigation has long been an unsolvable problem because of uneven temporal /spatial rainfall distribution. Based on past studies, it reveals that paddy field plays an important role in groundwater conservation; however, paddy field also requires a large amount of water for irrigation simultaneously. Furthermore, due to the impacts of climate change, the issue of uneven temporal/spatial rainfall distribution in Southern Taiwan has aggravated, which also affects plenty of hydro-meteorological variables, including the water level of Zheng-wun River, precipitation, temperature, and relative humidity (RH).

This study aims to unravel the nexus between specific agriculture acts, hydro-meteorological variables, and groundwater levels. As a result, the Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD) method and Time Dependence Intrinsic Correlation (TDIC) method are implemented to analyze the NDVI time series and hydro-meteorological variables. With the analysis of MEEMD, we can establish the most influential time scales of hydro-meteorological variables and fallow duration associated with the groundwater level. Besides, the time lag effect of fallow to water-table depth can be determined by applying time-dependent intrinsic correlation (TDIC) approaches.

Groundwater is one of the valuable water resources worldwide; therefore, this study provides insights into the response of water-table depth to the non-linear, non-stationary hydro-meteorological variables. Additionally, we also formulate a new strategy for groundwater conservation by regulating the fallow duration.

Keywords: Fallow duration; Water-table depth; Hydro-meteorology; Time-frequency analysis (TFA); MEEMD; TDIC