A “mega-drought” on the Colorado river

Hard hit by drought the Colorado river is at the centre of concern in southwestern America, since it is vital for seven states. On 25 May, the level of Lake Mead – the largest American reservoir – fell to 44 metres below its usual height, and there is no sign of it rising. The latest forecasts issued by the federal government are critical, as they predict a threshold of shortage in 2022 and that severe restrictions on water use will be necessary in Arizona, Nevada and Mexico.

A drying river

Many scientists describe the last two decades in this region of the USA, already marked by the scars of climate change, as a “megadrought”. The river has suffering from the impacts with a discharge reduced by 20% since the beginning of the century. “We will have wetter and drier years in the future, but the generally hotter temperatures mean that we must expect a drier basin with less water, estimated Laura Condon, assistant professor of hydrology and atmospheric sciences at the University of Arizona, Warmer temperatures increase the quantity of water used by plants and in time decrease the snow mantle. Even if we have the exactly the same quantity of precipitations, a warmer basin will mean a lower discharge in the river.”

The reduction of the snow mantle is already marked throughout the American west. It obviously has an initial impact on the discharges of the river in the spring and summer. The meltwater is also absorbed by the soil instead of replenishing the surface water.

A dark future

These are long term changes on the scale of the basin and will require collective action and cooperation. If we continue to have forever less water in the river, we’ll need to reach agreement to face up to this new reality”, explained Laura Condon.

Confronted by the urgency of the situation, the Biden administration has announced that it will establish an interagency workgroup to deal with the exacerbation of the drought in the west. The aim is to also support the communities and workers affected by this shortage, which are already making efforts regarding water consumption. However, scientists fear that the hypotheses expressed by this group are based on optimistic outlooks and “do not fully render account of the aridification of the Colorado river basin caused by climate change” (Eric Kuhn, a researcher specialised in water).

Faced with this disaster in the making of a river system supplying more than 40 million people, Professor Amir AghaKouchak, of the Department of Earth Sciences at Irvine University, asserted: “we have to prepare for a basically different hydrological cycle”.

In the case of a shortage of level 2 – which according to the estimations of the USBR (United States Bureau of Reclamation) could occur by the end of 2022 – obligatory water supply cut-offs will be enforced in Arizona, Nevada, Mexico and California.