That appears to be a normal climate thing around the Caribbean ~ and no SUVs.
Then, Sometime after 1541 a drought started somewhere in what is now the United States ~ or, in fact, it could have started before 1541 if we read DeSoto's diary/guidebook as indicating he and his band of explorers crossed the Great River at Leven's Worth Indiana.
It's pretty obvious there was a drought going on because the expedition traveled in open country virtually the whole way to Chicago ~ from Central Florida!
Some detailed studies have been done by archaeologists and they find evidence that pre-Colonial Virginia was in a drought that was at least 70 years in duration in the 1500s, and during that period there was a 17 year period with no precipitation at all!
Virginia's drought was in full blown splendor when Smith and crowd settled Jamestown (1609). It was 1620 before there was serious European interest in other large scale settlements ~ we may infer from that attitude that there was a water shortage along the East Coast.
What that means to the interior is just as serious ~ no water, no people! That also means the Mississippi main watershed (the Ohio Valley) was equally difficult to settle in that period ~ and the Iroquois might well have not had to kill many of them to get them to go somewhere else while they took over the region.
With the Upper reaches of the Mississippi and Missouri out of the running as reliable routes of travel, the main thrust of Spanish development would have hugged the Gulf Coast ~ which it did, and Texas ~ if they could ~ as hurricanes returned after the Great North American drought of the 1500/1600 period settlement was probably intermittent and difficult ~ which, in fact, it was, until the 1700s.
A 200 year drought in Sumer would have definitely caused some problems ~ first of all, they'd moved upstram into Turkey, and Kazan, and probably on up into Europe.
Much of the United States is at the same latitude as North Africa, Persia, the Gobi ~ and other desert regions.
Just a few years without regular replenishment with rain from Gulf hurricanes and this place returns to its natural desert state! Of course the entire Eurphrates basin is subject to the same sort of droughts.
Think you're getting a little over-enthusiastic there. DeSoto probably didn't get any farther north than the MO bootheel.
Also the country he traveled thru is described as heavily populated, which no doubt explains to some extent why it was "open." Also large populations don't go along real well with desert conditions.