In this study, the long-term trends of hydrometeorological parameters, including precipitation, river discharge, Leaf Area Index (LAI), snow cover, and evapotranspiration (ET) in the Dez River basin were investigated over the period from 2002 to 2021 using ground-based and satellite data. Satellite data were extracted from the Google Earth Engine platform, and for trend analysis, the modified non-parametric Mann-Kendall (MMK) test, which removes the effects of autocorrelation, along with the Sen's slope estimator, were employed. The results indicated that most rain gauge stations showed no clear and significant trend in precipitation, with only Dorud station recording a significant decrease and Venaei station showing a significant increase. In contrast, the analysis of river discharge revealed a predominantly decreasing trend across the basin, particularly at the Sabbe Cham-Chit and Tele Zang stations, where significant decreases were observed at the 95% confidence level. Remote sensing data also indicated that snow cover experienced a significant decreasing trend at the 90% confidence level, while the Leaf Area Index showed a significant increase (Z=2.43). The evapotranspiration parameter exhibited no significant trend, which could be attributed to limited water resources and a balance between increased vegetation cover and soil moisture deficit. Overall, the findings indicate a decline in surface water resources due to a combination of climate change and human activities, highlighting the need for smart and sustainable water resource management and the evaluation of adaptation scenarios.