IN their natural state, the rivers of the Indus basin have four distinct mechanisms of water supply — snowmelt, glacial melt, rains and groundwater seepage. Snowmelt starts adding water to the tributaries of the Indus in March and April. By the time the snowmelt wanes, glacial melt kicks in in late April, reaching its apogee by late June. When the glacial melt is at its peak, the monsoon sets in too. Between July and early September, the rivers flow to their brim and spread out wide in the floodplains, recharging the aquifers adjacent to the rivers. October through December, the rainfall is negligible and there’s no snowmelt/glacial melt feeding the river, but the groundwater recharged into the aquifers starts seeping into the river. Winter rains from January to March, along with groundwater seepage, continue to feed the river system until the cycle of snowmelt begins again. The glaciers, the monsoon, the snowmelt and the aquifers evolved over millions of years and created one of the most reliable and consistent hydrological miracles of nature.