Science et changements planétaires / Sécheresse


Water and soil management in the Hydrological Region 36 (HR 36) of North-Mexico Volume 13, issue 4, Décembre 2002


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Mission IRD, BP 434, 1004 Tunis El Menzah, Tunisie.
  • Page(s) : 226-34
  • Published in: 2003

The Hydrological Region 36 (HR 36), with a surface area of 92,000 km2, is one of the three Mexican hydrological endorheic regions. North of the tropic of Cancer, at a latitude of 23° to 27° north, the HR 36 stretches from the Western part of the Sierra Madre, which is more than 3,130 meter high, to the lagoons of Mayrán and Viesca. These lagoons are the outlets of the Ríos Nazas and Aguanaval on the high plateau of North-Mexico (Altiplano) at an altitude of 1,100 m. The analysis of the annual rainfall with a sample of 123 pluviometric stations made it possible to distinguish three areas in the HR 36: a sub-humid area on the western part of the Sierra Madre, a semiarid area on the piedmont of the Sierra and an arid area on the high plateau. Thirteen units of the FAO/Unesco soil classification are present in the HR 36, but only three units occupy 70% of this region: the litosols, the xerosols and the feozems. The vegetation counts four main groups but the xerophile matorral, a dense enough shrubby formation, which is drought-resistant, is predominant (60% of the surface area). Pluvial farming (mainly maize and bean) is practised in the valleys of the higher part. In the semi-arid area, an additional irrigation makes farming exploitation possible. In the arid area, only irrigation through the mobilisation of surface and ground waters has allowed intensive farming to be developped first around cotton farming and more recently around fodder farming for cattle-rearing geared towards milk production. Ranching is developed all over the HR 36 but the mean density on the pastures is very unequally distributed. On average, the livestock should be a head of cattle per: 4 hectares in the sub-humid area, 15 hectares in the semiarid area, 85 hectares in the arid area. The overexploitation of the forest in the sub-humid area and the overexploitation of the pastures threaten the viability of these production systems. In the lower and arid part, the overexploitation of the water table underground has involved a steady drop in the water level equal to 1.5 meter per year and a rising salinity of irrigation waters. This salinity has now become a serious problem for this intensive production system.