What has the biggest impact on a region, weather or atmosphere.

Weather.

You see how the weather is in a certain place can determine how the plant life and just life in general would live. It can also effect people. Let's say there was a drought somewhere, this would effect people whereas, they could lose a significant source of water and food because it would make them likely have to find a new water source or the animals would. Weather also effects the land in harmful ways. For example when it floods, the ground gets muddy but can also get so muddy below a certain area, that the soil entirely collapses into the ground (that would be a sinkhole).

There are picture below to show you some of the effects.

-R3TR0 Z3R0

the answers would be

the first one and the second one