| Popis: |
Long-term trends in groundwater levels over the contiguous United States (CONUS) have been investigated for water resource management. Numerical modeling or remotely sensed data are frequently utilized as analytical tools; however, observational data on the CONUS have rarely been used. This study explored observational groundwater levels at 642 wells across the CONUS from 1990 to 2019. Wells with less than 30% of missing data over 30 years were selected, and trends in their groundwater levels were assessed using a Seasonal Mann-Kendall’s test and Sen’s slope. Trends in three climatic variables (precipitation, maximum temperature, and minimum temperature) were simultaneously analyzed. The results showed that trends and the degree of change in groundwater levels varied spatially across the CONUS and were not correlated with those of the three climatic variables. The degree of change in the groundwater levels was small for the majority of wells (> 85%), with less than the absolute value of one Sen’s slope. Wells with more than the absolute value of one Sen’s slope showed declining trends in groundwater levels, emphasizing the need for groundwater protection. This study was limited in explaining the major drivers of groundwater fluctuations across the CONUS owing to the complexity of natural and anthropogenic drivers. Thus, it was concluded that multiple tools should be concurrently used to interpret groundwater dynamics across the CONUS to secure groundwater resources. |
