How did the ancient Americans in the Southwest adapt to the dry climate and unpredictability of rain fall in the region 3,500 years ago?

They began to form permanent settlements supported by corn cultivation.

Explanation:

According to the archaeologists, the earliest settlers of Native Americans came from Asia around 15,000 years ago to North, Central and South America through crossing Beringia. The ancient Americans in the Southwest adopted the dry climate and little rainfall region by indulging in the cultivation of crops like corn along with beans, and pumpkins. They also hunted rabbits and deer.