The Tensift watershed (20,000 km²) is located in Morocco around the city of Marrakech, in a semi-arid climate. It has two parts with a contrasting and complementary hydrological functioning: a mountainous part, upstream, acting like a water tower (the Hight Atlas, 4,167 m) with annual rainfall between 300 and 700 mm, which feeds a second part, an irrigated plain downstream (The Haouz of Marrakech, 450 m, 240 mm annual rainfall), occupied by tree crops (olive trees and citruses) and annual crops (cereals and market garden). Agriculture consumes about 90% of the basin’s water resources. A significant proportion of precipitation falls as snow, stored in winter, the melting of which contributes to the shifting of flows towards spring as well as to the recharging of aquifers allowing the support of base flows during the summer. The Tensift basin faces a growing pressure on water resource due to agricultural development (irrigated areas have tripled since the 1980s) and the increase of domestic consumption, which causes the aquifer level to drop about 1 to 2 m per year.
The Rheraya sub-basin (1000 to 4167 masl), located in the upstream part of the Tensift, is 60% occupied by low-permeability formations (eruptive and metamorphic rocks). The downstream of the basin is characterized by sedimentary sandstone-clay and limestone formations. The mountainous soils are thin and strongly weathered. The vegetation cover is very sparse on the slopes and areas of traditional irrigated crops are located near the talwegs (about 5% in surface).
The Tensift observatory allows to characterize the functioning of this semi-arid hydrosystem, in order to provide management tools for the territories and also to predict the evolution of water resources under different scenarios of global change. The scientific objectives are:
- To model hydrological processes, based on the complementarity between field observation and satellite image, in order to estimate the resource (snow dynamics and evapotranspiration in mountain and the contribution to flow and recharge of aquifers; functioning and water consumption of irrigated corps in the plains),
- To spatialize indicators of land surface functioning and to analyze their spatial and temporal variability for the understanding of the continental water cycle and the vulnerability of Mediterranean ecosystems.
Sites and measured variables
The experimental set-up is comprised of three nested spatial scales:
1) the Tensift watershed,
2) more studied sites (ex: irrigated perimeters, the Rheraya mountainous basin, 255 km²) and
3) intensively monitored sites, typically agricultural plots.
The observatory consists of about 12 complete weather stations (temperature, humidity, wind, radiation, rainfall, including two snow measurements stations at 3,200 m altitude) completed by 5 rain gauges.
Additional measurements of river flows, piezometry and irrigation volumes are available via local partners. The intensive sites measure water and energy flows related to the soil-plant-atmosphere system, complemented by vegetation observations (biomass, Leaf Area Index, leaf potential, etc.). Finally, land use observation campaigns are regularly carried out in the plain.
Partners and further information
The observatory is led by a consortium composed of Cadi Ayyad University (UCA, Marrakech) and the Centre d’Études Spatiales de la Biosphère (CESBIO, Toulouse). It is financially supported by the IRD (« South » label) and by Moroccan, French and European funded projects.