| Summary, etc. |
Groundwater is crucial for sustaining ecosystems, agriculture, and drinking water supplies, necessitating accurate recharge rate estimates for effective resource management. This study utilized the AquiMod 2 model to estimate groundwater recharge in Magnuang, Batac City, Ilocos Norte, based on a four-year time series of monthly groundwater level measurements from January 1995 to December 1998. The model calibration achieved a Nash-Sutcliffe Efficiency (NSE) of 0.71, indicating a good fit between simulated and observed levels. Recharge simulations for 1995-1998 was 81.78 mm, 155.53 mm, 53.45 mm, and 71.58 mm, representing 5.52%, 5.50%, 4.57%, and 4.86% of annual rainfall, respectively. During El Niño years, recharge was significantly lower, with values of 2.76 mm (2014-2015), 6.56 mm (2021-2022), and 4.26 mm (2023), corresponding to 0.76%, 1.80% and 1.17% of annual rainfall. Conversely, La Niña years exhibited higher recharge rates: 153 mm, 211 mm, 188 mm, 181 mm, and 185 mm, accounting for 5.42%, 6.96%, 6.00%, 7.01%, and 6.99% of annual rainfall. Normal years had recharge rates of 104.88 mm, 139.77 mm, 130.12 mm, 150.96 mm, and 88.24 mm, representing 5.38%, 6.93%, 6.57%, 6.76%, and 4.75% of annual rainfall. Statistical analysis confirmed significant variability in recharge rates under El Niño, Normal, and La Niña conditions, with mean recharge values of 4.24 mm, 122.80 mm, and 185.32 mm, respectively. El Niño conditions resulted in significantly lower recharge, while La Niña conditions showed higher recharge with greater variability. T test results indicated statistically significant differences in recharge across these climatic conditions. x Based on these findings, a comprehensive approach is recommended for long term groundwater sustainability. This includes stricter regulation and monitoring of groundwater extraction, the implementation of artificial recharge projects such as rainwater harvesting and managed aquifer recharge, and promoting water conservation through public education and advanced agricultural practices. Additionally, improved land-use planning that integrates water resource management can further support sustainable groundwater management in the region. |