Why are the northern Cook Islands especially vulnerable to drought?

The northern group of the Cook Islands is more vulnerable to drought than the southern group primarily due to their physical geography. Unlike the southern islands, which include high-volcanic landforms, most of the northern islands are low-lying atolls—narrow sandbanks resting on circular reefs.12

Because these islands lack rivers or significant freshwater streams, residents are entirely dependent on rainwater storage tanks and wells that tap into a thin, lens-shaped layer of fresh water stored within the island's coral structure. This limited capacity for natural water retention makes the northern atolls particularly susceptible to the impacts of drought on their agriculture and water supply.21