Groundwater Resource Assessment by Applying Long-Term Trend Analysis of Spring Discharge, Water Level, and Hydroclimatic Parameters.

Groundwater accounting is becoming increasingly important for sustainable societal development. To gain insights into the long-term spatiotemporal changes from 1992 to 2015 regarding groundwater resources in Kumamoto, southern Japan, we analyzed climatological time series, discharge from the groundwater-fed lake (Ezu Lake), and groundwater levels from 94 wells. To explicitly detect temporal changes in these variables and assess potential drivers of change, we used three different trend analyses: the Mann-Kendall Test (MKT), Seasonal Mann-Kendall Test (SMKT), and Innovative Trend Analysis (ITA). Our results revealed a consistently increasing trend in monthly mean temperature, monthly total precipitation, and maximum hourly rainfall. However, a decreasing trend was detected for the discharge rate from the Ezu Lake from 1992 to 2015. Among the 94 investigated groundwater wells, 64 wells showed an upward trend (p ≤ 0.05), while 23 wells showed a downward trend (p ≤ 0.05) for groundwater level. The observed decline in groundwater level is related to the decline in Ezu Lake discharge. However, the increase for the majority of groundwater wells is related to the increased precipitation and applied artificial groundwater recharge as well as a decrease in the groundwater abstraction rate. The ITA outperformed both SMKT and MKT, particularly in detecting minor variations in hydrological time-series data. The results and approach presented in this study can provide a scientific basis for improve groundwater accounting and water resources management in Kumamoto area and other regions with similar climate and socioeconomic conditions. [ABSTRACT FROM AUTHOR]