A single massive flood will not make a family move, but five years of small droughts will trap them in poverty forever.

Human migration is driven by the slow accumulation of environmental stress rather than a one-time disaster. While a flood is dramatic, families can often recover from it once. Repeated, smaller shocks like bad harvests slowly eat away at a family's savings until they are too poor to afford the cost of leaving. We often worry about climate refugees fleeing a sudden catastrophe. In reality, the biggest threat is the millions of people who become too resource-depleted to escape their deteriorating land.