Impacts of precipitation, land use change and urban wastewater on groundwater level fluctuation in the Yogyakarta-Sleman Groundwater Basin, Indonesia

Population growth and an increase in communities' economies have led to a worldwide rise in water demand. The development of urban areas will cause excessive groundwater extraction, which will trigger environmental impacts, including a decline in groundwater levels. Changes in rainfall, land use, and the volume of urban wastewater recharge patterns will affect groundwater level fluctuations over a period of time. This study investigates the effects of rainfall, changes in irrigated agricultural land, and urban wastewater volume trends on groundwater level fluctuations in the Yogyakarta-Sleman groundwater basin, Indonesia, from 2011 to 2017. Analysis of the trend of each parameter was performed using the Mann-Kendall test. The results showed that the recharge area had a trend of deeper groundwater levels positively correlated with the decrease of irrigated agricultural land. In contrast, precipitation trends and urban wastewater volume were negatively associated with the groundwater level fluctuation trend. In the transit area, shallow groundwater levels were positively correlated with precipitation and urban wastewater volume. In contrast, there was an opposite trend in the area of irrigated agricultural land. In the discharge area, groundwater levels became deeper, which positively correlates with precipitation and irrigated agricultural land, while the urban wastewater trend was the opposite. Increasing of groundwater level in the transit area was 0.21-0.25 m/year, where recharge and discharge areas had a decreasing 0.10-0.26 m/year. Import water from municipal water networks and urban wastewater recharge significantly contributed to rising groundwater levels in the transit area. It occurs because urban wastewater in the transit is evenly distributed, but in recharge and discharge areas, groundwater recharge from urban wastewater is localized. The urbanization process did not always negatively impact groundwater resources and contribute to groundwater recharge, depending on managing the urban sewage.