Courtesy of Robin Willoughby of Chatham House in London I have come across this interesting study about the water consumption of different crops in Saudi Arabia.
It was conducted by researchers of King Saud University on a research farm of King Abdul-Aziz University in Hoda Al-Sham in the Makkah area.
Like this earlier article in Al-Eqtisadiyah that is referencing a study of King Saud University it finds that alfalfa cultivation needs about four times more water on any given piece of land than wheat.
The wheat phase-out of the government has thus led to increased water consumption if farmers switched to alfalfa. In off-the cuff estimates some farmers put the water consumption of alfalfa even at five times higher and above in the hot summer months as I write in Oil for Food on pp. 87-88.
The increased water consumption is mainly due to all year round cultivation of alfalfa (which is essentially not uprooted, but only cut to let it grow again), while wheat is only cultivated 4 months in the winter. In addition, alfalfa plants also need about 20% more water than wheat:
The Evapotranspiration (ET) figures for wheat on p. 199 of the study and for alfalfa on p. 201 show this clearly:
Wheat: Period planted: 120 days, average ET per day: 3.87 mm, total ET over the year: 498,2 mm
Alfalfa: Period planted: 363 days, average ET per day 4.94mm, total ET over the year: 1922, 50 mm
Thus the increased water consumption of alfalfa according to this study is mainly due to all year long cultivation, but also due to an ET that is 20% higher than wheat. If Saudi Arabia really wants to save water, it will need to address alfalfa production and the continuous expansion of its dairy industry that requires it as feedstock.