Most of Central Asia is dry. Rain is scarce on the plains, summers are long and hot, and rainfall alone will not carry a crop to harvest. In the river valleys and oases, most crops grow only because water is brought to them.

That water begins far away, in the high mountains, and passes through rivers, reservoirs and canals before it reaches a furrow. This explainer follows its route and shows why sharing the water is never simple.

Two rivers from the mountains

Two great rivers supply much of the region’s irrigation water: the Amu Darya and the Syr Darya. The Amu Darya gathers its water in the Pamirs and neighbouring ranges and carries the more water of the two. For part of its course it runs along the northern border of Afghanistan, and then it flows on through Turkmenistan and Uzbekistan.

The Syr Darya rises in the Tian Shan mountains. It crosses the Fergana Valley, a densely populated farming region, and then runs through Kazakhstan. Both rivers head towards the Aral Sea.

Neither river depends much on rain falling over the plains. They are fed by snow that builds up in the mountains through the cold months and by glaciers that melt in the warm ones. The flow is therefore highest in late spring and summer, just when the fields need water most.

Glaciers work as a slow reserve: they go on releasing water in hot, dry spells when the snow has already gone. Many glaciers in these mountains are retreating as the climate warms, which makes that reserve less dependable over time.

Electricity in winter, irrigation in summer

The mountain countries upstream, Kyrgyzstan and Tajikistan, have steep valleys well suited to dams. They use the water to generate electricity, and they need that electricity most in winter, when homes must be heated and lit. Sending water through the turbines in winter draws the reservoirs down.

The countries downstream, Uzbekistan, Turkmenistan and Kazakhstan, have wide plains and large irrigated areas. They want the reservoirs to fill in winter and to release water in summer, during the growing season. Water let go in winter cannot be used on the fields, and it may even cause flooding along the lower river.

Neither side is in the wrong; the same water simply cannot do both jobs at once. That is why the countries of the basin coordinate releases through joint bodies and agreements, and why water and energy are so often discussed together.

Canals and irrigated fields

From the rivers, water is led into main canals, then into smaller channels and finally into ditches at the edge of each field. Irrigation here is very old: oasis farmers dug canals long before modern machinery existed. During the Soviet period the network was greatly enlarged, chiefly for the sake of cotton.

Cotton and wheat are among the main irrigated crops, grown alongside rice, vegetables, fruit and fodder. Much water is lost on the way: unlined earth canals leak into the ground, and open water evaporates in the heat. Where too much water is applied, the water table rises and salt builds up in the soil, which lowers the yield.

What happened to the Aral Sea

The Aral Sea, on the border of Kazakhstan and Uzbekistan, was once one of the largest lakes in the world. It has no outlet, so its level depended on what the two rivers delivered. As more and more river water was taken to irrigate fields, too little reached the lake, and it shrank.

The sea broke into separate bodies of water, and much of its former bed became a salty desert. Fishing towns were left far from the shore, and the wind lifts salt and dust from the dry bed. A dam in Kazakhstan has helped the smaller northern part to recover to some degree, while hardy desert shrubs are planted on the dried seabed to hold the soil.

Using less water

The same harvest can be grown with less water. Drip irrigation delivers water through tubes straight to the roots, so little is lost to evaporation. Lining canals with concrete or another waterproof material cuts leakage, levelling fields helps water to spread evenly, and choosing crops that need less water eases the pressure on the rivers.

Households have a part to play as well. Mend dripping taps and leaking pipes, do not leave water running, and water the garden early in the morning or in the evening, when less of it evaporates. Sweep a yard rather than hosing it down, and keep drinking water for drinking rather than for washing the street.

None of these steps looks like much on its own. Repeated across many farms and homes, they decide together how much water is left in the river for those who live further downstream.