Mexico, a classified arid and semi-arid country, has a total land area of 2 million square kilometres, 23% of which is equipped for irrigated agriculture. The agricultural sector plays an important role in the economic development of the country accounting for 8.4 of agricultural gross domestic product (GDP) and employing 23% of the economically active population. Irrigated agriculture contributes about 50% of the total value of agricultural production and accounts for about 70% of agriculture exports. Mexico's government initiated a number of structural reforms in the water sector aimed to introduce modern water management and irrigation.
Development
Infrastructure Of the 62,000 square kilometres with irrigation facilities in Mexico, about 42,000 km2; (67%) are irrigated with surface water, and the remaining, some 20,000 km2; (33%) are served by groundwater pumping. Approximately 33,000 km2; correspond to 80 bigger systems, namely irrigation districts (Distritos de Riego – DR). The remaining 29,000 km2; are distributed among more than 30 thousand small size communal and irrigation units (Unidades de Riego – UR). The average plot size is relatively small, less than 1 ha is common, particularly in the irrigation units. At the same time, many landowners have farms larger than 50 ha and family farms, combining individual land holdings, may surpass 500ha. Irrigation infrastructure and irrigated area
Source: FAO The most important irrigation projects in Mexico are: Culiacán-Humaya-San Lorenzo Project, Yaqui River Project, Fuerte River Project, Colorado River Project, Lower Bravo River Project, Higher Lerma River Project, Lagunera Region Project, Guasave Project, Mayo River Project, Lázaro Cárdenas Project, and Delicas Project. These projects range from some 2,500 km2 to around 800 km2 of irrigated area each one.
Linkages with water resources
The mean annual rainfall of 777 mm results in a mean annual runoff of 410 km2, slightly more than 62 km3 of yearly renewable groundwater (including an estimate of 15 km2 of induced replenishment in the irrigation areas), and the remaining, some 1,060 km2, evaporates. Most of the country experience in rainy season, from June to mid-October and significantly less rain during the remainder of the year. February and July generally are the driest and the wettest months, respectively. Less than a third of the runoff from precipitation occurs within 75% of the national territory, where most of the irrigated land is located. In 1995, 61 km3 were used for irrigation, 67% of which was supplied by superficial water, 33% from groundwater. Only 40 km3 were actually used, due to inefficiencies related with water canals and evapotranspiration. There are three main watersheds in Mexico: the Western or Pacific Watershed, the Eastern or Atlantic Watershed (Gulf of Mexico and Caribbean) and the Inland Watershed, where rivers do not empty out into the sea. Two thirds of the country's 146 rivers drain into the Pacific Ocean. There are approximately 100 rivers in the Western or Pacific Watershed, the most important in terms of water flow being the Balsas, Colorado, Culliacan, Fuerte, Lerma-Santiago, Verde, and Yaqui rivers. The Eastern Watershed is made up of 46 main rivers, the most important being the Bravo, Coatzacoalcos, Grijalva, Pánuco, Papaloapan and Usumacinta Rivers. The Inland Watershed is made up of large closed basins. The Nazas-Aguanaval river system is the largest.
Environmental impact
More than 22 km3 of waste water are discharged into Mexico's water bodies. Agricultural use accounts for 50% of this volume, mainly in the form of nonpoint discharges with high levels or residues for pesticides, fertilizers, and other chemicals. Vast expanses of southern and southeastern tropical forest have been denuded for cattle rising and agriculture. Deforestation has contributed to serious soil erosion nationwide. In 1985, the government classified almost 17% of all land as totally eroded, 31% in an accelerated state of erosion, and 38% showing signs of incipient erosion. Soil destruction is particularly pronounced in the north and northwest, with more than 60% of land considered in a total or accelerated state of erosion. Fragmented because of its semiarid and arid character, the soil in this region has become increasingly damaged through excessive irrigation with waters high in salt. As a result, desertification is spreading throughout the region. Ineffective irrigation has generated salinization and drainage problems in 384,163 ha in a total drained area of 5,203,346 ha.
History
Irrigation development in Mexico was a governmental concern during the Porfiriato and was affected by the Mexican Revolution and the agrarian reform. At the beginning of the Revolution (1910), there were about 1.2 million ha of irrigated land. Much if this land had been developed by land companies, mainly American, to grow plantation crops such as sugar cane and cotton. After the creation of the National Irrigation Commission in 1926, the irrigated area quickly expanded, and the agricultural census reported a total of 4.3 million ha of irrigated land by 1960. By the late 1980s, Mexico had about 6 million ha under irrigation. During the 1980s and 1990s, irrigation development slowed down due to the economic crisis. The irrigation sector focused then on optimizing the use of existing infrastructure. In 1997, the total irrigated area accounted for 6.2 million ha, 5.4 million ha were actually irrigated. The northern states of Sinaloa and Sonora, account for 15% and 11% respectively of the total irrigated land.
… excerpt ends here. Continue reading the full article.
