Comparison of different techniques in determining groundwater levels trends in Türkiye

Abstract

Groundwater represents one of the largest resources of freshwater in the world. Thus, investigations of groundwater level variations due to climate change and increasing human activities are of great importance, especially in resource scarce regions. Our research aimed to understand the long-term effects of climate events and water use on groundwater levels over the study area via Mann-Kendall, Sen's Slope, Innovative Polygon Trend Analysis (IPTA), and Innovative Trend Analysis (ITA) analyses. Although several studies are available in relation to GWL trend analysis via ITA, Mann-Kendall and Sen slope in the literature, there are few IPTA studies conducted. The focus of the study was seven wells across T & uuml;rkiye over the period 1987-2022. Results demonstrate that there was a downward trend in GWL in all stations annually, regardless of the method. At monthly scale, a decrease was noted, especially in June, August, and September, while seasonally, decreases were seen in autumn and winter. Moreover, it was evident the results of the Sen slope and ITA were compatible, while the IPTA was a useful tool in detecting GWL trends. Identifying and understanding GWL trends is highly valuable in informing groundwater resource managers of critical areas of overuse and other factors affecting groundwater, resulting in preventive interventions to overcome such problems and protect this critical resource. GWL trends are analysed at the monthly, seasonal, and annual scales using a combination of techniques, such as Mann-Kendall, Sen's Slope, Innovative Polygon Trend Analysis (IPTA), and Innovative Trend Analysis (ITA), using data monitored between 1987 and 2022 in seven wells in Turkey. Trend analysis will allow for evaluating differences among commonly used methods in investigating GWL levels, eventually providing insights on critical areas to prioritize interventions. Besides analysing trends, a homogeneity analysis was conducted to detect change points in groundwater levels. image