Measuring water
p. 132
Résumé
Humans are putting mounting pressure on water resources. They use water for drinking, washing and, above all, irrigation purposes. Eighty percent of the water abstracted is intended for agriculture, which poses a significant challenge in regions where freshwater is increasingly scarce.
Texte intégral
1Farmers use water to irrigate their fields, but the amount withdrawn is not clearly known, even to water management agencies, a fact which is not without consequences for the environment or the populations. The absence of quantification makes it difficult to estimate the pressure on the water table and avoid excessive withdrawals. In an attempt to remedy this situation, in the early 2000s a scientific programme was established in a semi-arid region of Morocco to determine the amount of water needed for every crop, as well as the amount used by farmers for irrigation purposes. When is irrigation necessary and how much water should be applied?
Rural landscape in Morocco.
© IRD/G. Michon
2Researchers started working in the field to measure evapotranspiration and the water balance as accurately as possible for various types of crop and under various weather conditions. They came up with values which they used to model the water consumption of Moroccan crops based on the weather and high spatial resolution satellite data to monitor plant growth over time and space. They were therefore able to determine the quantity of water used in agriculture for vast territories.
Modelling of a valley in Morocco.
© IRD /
3They developed an initial version of the SAMIR model, a platform intended for water management bodies to better gauge the quantities withdrawn for the agricultural sector. However, the routine use of SAMIR was impeded by the high cost of high-resolution satellite images and their insufficient frequency. These two obstacles were removed with the launch, in 2015 and 2017, of the Sentinel 2 satellites of the Copernicus European programme, which provide free, very high resolution images of every spot on Earth every five days. The SatIrr model was later created to respond more specifically to the need to manage each irrigated parcel. This is accessible online for free, advising farmers on the amounts of water required. Tailored to the Mediterranean region at present, it will soon be configured for damper climates, such as that of southern India.
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