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The populations become completely separated from one another</span>
Answer:
Trade winds are located 0–30 degrees latitude in both the southern and northern hemispheres. The wind which flows towards the pole between Polar Easterlies and Trade winds move westwards because of Coriolis forces. These winds are called Prevailing westerlies.
I think the two sources would be drip irrigation which is like a river, lake, groundwater, etc... The second source could be is making a new irragation system that could deliver water faster.