Assessment and future projections of groundwater depletion and seawater intrusion in the coastal aquifers of Karachi

Groundwater beneath Karachi is falling by half a metre to a metre every year, and the sea has already pushed 6.41 kilometres inland to fill the space it leaves. Pakistan’s largest city draws heavily on water stored underground right against the Arabian Sea, and once saltwater reaches a well, that well is finished. A computer model of the city’s groundwater, calibrated against years of well readings, rainfall records and land use change, was used here to test four plausible futures. Under the mildest, the salt front reaches 8.1 kilometres inland by 2043; under the harshest, combining reduced rainfall with doubled pumping, it reaches 17.78 kilometres and overtakes major urban and industrial districts. Those distances and dates turn a familiar warning into a schedule, and make the case for capping extraction and deliberately replenishing the water underground while that is still worth doing.

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