Groundwater, as a vital water resource in arid and semi-arid regions, plays a crucial role in sustaining human livelihoods, agriculture, and industry. Over recent decades, these areas have witnessed rapid groundwater depletion, raising concerns about resource sustainability. This research provides a comprehensive analysis of the factors contributing to the decline in groundwater levels (GWL) within the Marand Plain, a heavily exploited area with complex groundwater dynamics in northwestern Iran. To achieve this objective, a novel approach based on Maximal Overlap Discrete Wavelet Transform (MODWT) entropy analysis was introduced to explore the complexities governing the groundwater system across various periods. The next step involved conducting a nonparametric trend analysis of the GWL through Mann-Kendall tests to interpret declining trends in relation to hydro-climatological factors and vegetation dynamics represented by NDVI. In the final phase, the study employed Wavelet Transform Coherence (WTC) and Partial Wavelet Coherence (PWC) to thoroughly examine scale-dependent control of various surface factors within the groundwater system., The findings indicate a limited impact of climate change parameters on the GWL decline. However, the results highlight the significance of vegetation dynamics, driven by land use changes, as a primary factor contributing this decline.