Understanding how soil moisture influences the exchange of water and energy between land and the atmosphere is key to predicting droughts, heatwaves, and climate patterns. A critical threshold of soil moisture separates two major land surface conditions: when water limits evaporation (water-limited) and when energy from the sun limits it (energy-limited). Traditionally, this threshold is estimated using complex surface energy flux data. In our work, we introduce a simpler method that uses satellite observations of soil moisture and daily temperature swings in the soil (diurnal temperature range) to identify this threshold more reliably across the globe. We tested this new approach in different climates using both satellite and reanalysis data. Our method closely matches traditional techniques and reveals seasonal shifts in evaporation regimes - showing, for example, that many dryland areas are water-limited most of the year. We also found that shallow and deep soil layers often behave similarly, meaning surface soil data can help us understand what’s happening below ground. These insights can improve drought monitoring, climate models, and our understanding of land–atmosphere interactions.