Final answer:
21st-century climate change is expected to change the prevalence and distribution of waterborne diseases by expanding the habitats of disease-carrying insects and altering rainfall patterns.
Step-by-step explanation:
The human health impact expected from 21st-century projected climate change includes changes in the prevalence and distribution of waterborne diseases. Climate change can alter where organisms live, directly affecting human health by expanding the range of disease-carrying insects and accelerating their lifecycles. This will lead to diseases such as malaria, dengue fever, and West Nile virus spreading to new regions. Moreover, extreme weather events and shifts in rainfall patterns due to climate change may lead to increased instances of waterborne diseases.