Heat used to be an event. Now it’s an address. In the Global South’s hottest belts, days above safe wet-bulb thresholds are stacking up like unpaid bills, pushing families first to nearby towns, then to megacities that were never planned to receive them. The story we tell ourselves is that this is temporary — one bad season, one failed harvest. The data say otherwise. Heat is not a pause in life; it is the force that redraws where life is possible.

The Slow Emergency

Disasters are visible; heat is quiet. Crops fail without drama, construction shifts to night work, schools shorten hours, clinics see more dehydration and kidney stress. As these micro-shocks accumulate, households de-risk the only way they can: they move. First internally, to peri-urban fringes where rent is cheap and services are scarce. If income stalls and another heat season arrives, the move becomes permanent — not declared, just lived.

Urban governments face a math problem more than a moral one. Water, power, drainage, and transport were sized for yesterday’s climate and yesterday’s population. Informal settlements grow faster than serviced housing; night-time economies replace daytime labour; heat-proofing turns from a design choice into an employment policy. Cities that adapt fastest — shading, cool roofs, reliable water, predictable transport — become magnets for climate movers. Those that don’t become bottlenecks where poverty queues under a hotter sun.

The New Economics of Movement

Migrants do not carry only bags; they carry demand. Heat migration builds new markets in cooling, water storage, shade infrastructure, and night logistics. It also exposes a trap: the poorest households spend more of their income staying cool — fans, ice, diesel for backup power — than improving their prospects. That “cooling poverty” tax turns climate exposure into a balance-sheet problem. When compliance rules increase remittance costs, less money reaches the households that are already paying more to survive heat.

Labour markets are adjusting on the fly. Factories shift shifts; delivery and construction move into cooler hours; outdoor work rotates or automates. The firms that win are those that treat heat-proofing as production planning, not corporate virtue. For governments, the least sexy investments — shade trees, water mains, bus shelters — now have a fiscal multiplier. Cooler commutes, fewer sick days, steadier shifts.

Why “Temporary” Became “Permanent”

In flood or storm, a narrative of return makes sense. In chronic heat, return is a slogan that melts under the sun. Once a family reconfigures income around night work and a child’s school adapts its hours, the old village is no longer home; it’s an origin story. Urban districts change too: informal rental markets grow, women’s labour force participation shifts, young workers chase cooler microclimates within the same city block — under an overpass, near a park, beside a canal.

Policy that treats this as stopgap will always be late. The honest frame is permanence, then dignity: people will not go back; services must go forward. That means mapping heat at street level, prioritising shade corridors along bus routes, and pricing water like a right with metering that discourages waste without punishing the poor. Land-use rules can mandate reflective roofs and cross-ventilation; finance ministries can underwrite community cooling centres the way they underwrite clinics.

What Works (and What Doesn’t)

Works: cheap shade and reflective surfaces; district cooling for dense zones; water reliability; night transit; wage calendars synced to heat alerts; micro-mortgages for heat retrofits. Each is low glamour, high return. Cities that publish hourly heat-risk maps and tie them to labour guidance see fewer health shocks and steadier output.

Doesn’t: scattershot gadget fixes without grid upgrades; housing projects that ignore airflow; fee hikes on remittances; emergency-only policy. Heat is a system. Systems only respond to other systems — transport + water + housing + labour — and a cadence the public can understand.

The Choice in Front of Us

The choice is not between movement and stasis. Movement has already happened. The choice is whether we professionalise it. If we do, the “heat refugee” becomes a neighbour with predictable water, a cool route to work, and a child who can learn in the afternoon. If we don’t, the next hot season will read like the last — except the lines at the clinic will be longer.

The Global South is not waiting for permission. Mayors are painting roofs, rerouting buses, planting shade, rewriting building codes, and bargaining for lower remittance fees. This is how a civilisation adapts: unglamorous, relentless, daily. Heat doesn’t negotiate. But policy can — with physics, with budgets, and with time.