The correct choice for connecting two different regions where people are changing residence locations is **migration**.
Here's a brief distinction between the provided terms:
1. **Migration**: This refers to the movement of people from one place to another, often with the intention of settling temporarily or permanently in a new location. It is the most direct force connecting different regions through the movement of individuals.
2. **Globalization**: This term encompasses the increased interconnectedness of economies, cultures, and populations around the world, often through trade, communication, and technology. While globalization can influence migration patterns, it is broader and does not directly refer to the movement of people.
3. **Runoff**: This involves the flow of water, often from rainfall or melting snow, across land surfaces into bodies of water. It is not related to human movement.
4. **Nutrient pollution**: This refers to the excess nutrients, like nitrogen and phosphorus, entering water bodies, leading to environmental issues such as algal blooms. This term is also unrelated to human migration.
Thus, the most relevant term in the context of changing residence locations is **migration**.