Investigating the effects of groundwater level changes on GNSS observations in the Konya Closed Basin

The Konya Closed Basin (KCB), inhabited by approximately 4 million people, has a semi-arid climate and has been an important agricultural and economic production area with its fertile alluvial soils. In recent years, groundwater use as a primary source in the intense need for irrigation due to climate change, drought, and wrong agricultural policies tri-ggered land subsidence in the basin by causing the aquifer system compaction. In this study, the effects of groundwater level changes obtained from groundwater monitoring stations on the positions of continuously operating GNSS stations located in KCB were investigated by time series analysis. As a result of trend component analyses of time series processed based on the ITRF08 fixed frame, it was determined that the horizontal positions of stations in this region were moving in the northeast direction (18.74 mm/year). For the up coordinates, while stations ANRK, KLUU, and NIGD had move-ments 0.56 mm/year in the up direction, the other stations moved in the down direction. The vertical movement of the KNY1 station based on 560-day data was in the down (-) direction, with an annual movement of 70.96 mm, and this was the maximum movement or velocity compared to the other stations in this region. The trend analysis of 19 wells revealed linear groundwater level changes in the down direction with a mean value of-39.22 cm/year. The decrease in the water level of the wells in the Konya Closed Basin was statistically significant for the majority of the wells and at meter level in some wells. It was determined that the linear decrease was generally caused by the reduced groundwater level in this region. The periodic component analysis showed that the movements of the GNSS stations changed from a day to a year due to several factors, such as atmospheric and hydrological loading and climatic effects.

Automated summary

The study investigated the effects of groundwater level changes on the positions of GNSS stations in the Konya Closed Basin. It was found that horizontal positions of stations were moving in the northeast direction, while vertical movements varied among different stations in the area.