Final answer:
The change in the Blue Nile and Atbara rivers is primarily caused by rainfall and is important for water availability and economic activities along the rivers.
Step-by-step explanation:
The change in the Blue Nile and Atbara rivers is primarily caused by rainfall. When there is heavy rainfall in their respective catchment areas, these rivers experience an increase in water level and flow. This is important because it affects the availability of water for agriculture, hydroelectric power generation, and various economic activities along the rivers.
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