Drylands face more threat from droughts under global warming. It remains insufficient in quantifying the roles of potential evapotranpiration (PET) and precipitation (P) to drought changes in a warming climate. Thus, we quantified the relative contributions of PET and P and projected their future changes across global drylands under four scenarios from Phase Six of the Coupled Model Intercomparison Project (CMIP6) models. In the 21^st century, the multimodel medians of hydroclimatic fields indicate relatively consistent trend patterns, showing a drying over most of global drylands except for East Asia, Middle East, Sahel and South Asia drylands. The standardized precipitation evapotranspiration index (SPEI) presents a robust and ubiquitous drying with scenario-dependent magnitudes. The fractional contributions of PET and P to the present-day drought changes are estimated to be approximately equal (~50%). For the near- and mid-term projections, PET (P) contributes ~58% (42%) and ~61% (~39%), respectively. In the long-term, the fractional contribution of PET (P) reaches ~65% (~35%), ~72% (28%), ~80% (~20%), ~85% (~15%) under four different scenarios, respectively. Furthermore, PET contributes more significantly in the North Hemisphere than in the South Hemisphere, particularly over the Mediterranean, central and East Asian drylands. Drought conditions tend to be relatively stable under low scenarios (SSP1-2.6 and SSP2-4.5), while exacerbate continuously under high scenarios (SSP3-7.0 and SSP5-8.5). By the end of 21^st century, severe droughts like the present-day 1-in-20-yr events are estimated to become fairly common across global drylands. These results provide further understanding for making policy and adaption strategies for drylands.