Pretty much anywhere summer temperatures are consistently 21C/70F or greater, which is warm enough to spur growth of both Echinopsis plants and their amazing flowers.
How wet or dry the climate may be matters little to Echinopsis. I live in super humid Florida and mine do just fine. Now, just to be clear, I’m not saying you can plant Echinopsis out in the open in Florida or a similar climate and that they would do well in the virtually daily rain of summer. No, that would mean their roots would be sitting in water almost continuously … the one sure no-no. I keep mine in pots under the eves of my house and out of most of the rain. But they’ve done just fine here in Florida despite the fact the humidity rarely gets below 80%.
Echinopsis also tolerate cold temperatures well during winter months. Obviously, however, they must be brought inside during hard freezes or their water-filled bodies will freeze as well.