Exploring the relationships between hydro-climatic variables and water balance components in hydrologically complex basins is crucial for providing solutions compatible with future crises. In this study, hydro-climatic factors, including precipitation (P), actual evaporation (Ea), land surface temperature (LST), snowmelt (SM), snowfall (SF), and the amount of agricultural and forest vegetation (Aveg, Fveg) on the Precipitation Efficiency changes (P-Ea) of the two mega basins of Great Karun and Karkheh in the west of Iran were investigated. Initially, reanalysis data (ERA5-Land), remote sensing data from the Landsat series (1985-2022), and data from 56 meteorological stations were collected. Then, the trend of monthly hydro-climatic data changes and the correlation between ground data and data derived from ERA5-Land were calculated. The results from the months of January-March (wet season) in both basins showed steeper temperature changes with a gradient of 0.05-0.1 degrees C/month. Nevertheless, a decreasing slope (- 0.23 to - 0.03 mm/month) was observed for P in the same months (January-March). The changes in streamflow rate at the outlet of the Great Karun Basin have decreased by about 50% (for Ahwaz station), 48% (at Tange-Panj station), and about 80% in the Karkheh river flow during the studied period. The results of this research showed that the combination of ground and remote sensing data can provide a comprehensive view of the water resources status of the mega basins that undergo human interventions to manage the risk caused by water stresses. In addition, the findings are important basis for quantifying changes in the water balance to respond to changes in hydro-climatic factors.