Are mega-cities viable? A cautionary tale from Mexico"

Ezcurra, E and Mazari-Hriart, M (1996)  “Are mega cities viable ? A cautionary tale from Mexico - -Environment; Jan 1996; 38, 1; ABI/INFORM Global

• Centralism is the new trend as is megalopolis. Not clear of environmental impacts. Inverse relationship between GNP and pop growth. Resource shortages, air,water, energy, food supply and contamination all critical issues. Mexico is an ongoing experiment where conclusions yet to be drawn. The growth of the basin of Mexico is main concern. 18 million occupying same area. Forshadowings ominous for some. Environmental crisis situation would be from exhaustion of water, degredation of air, silting of drainage, and citywide flooding due to deforestation.
• Environmental setting -  Mexico is set in a hydrologic basin which was artificially opened in 1600’s. Before human transformations nine major environmental zones. Little of the original ecosystems remains. City has overtaken former lakebeds which have been progressively drained.
• Population and land use – exact numbers have been debated. Some say 15 (m) however last census in 1990.     Has traditionally been one of the most densely populated areas with estimates of 17.3 (m) in 1995. There has been an ongoing phase of merging of municipalities – now Mexico city (16 delegociones and 26 municipalities), Toluca (six municipalities), Puebla (8 municipalities) , Cuernavaca-Temixo, Jiutepec and Cuaula-Yautepec (aggresgation of smaller municipaities). Mexico City formed a megalopolis by merging with Tolouca and Cuernavaca.  As it expanded -> greater density, less planned, less open space.  Often built on hillsides -> erosion and flash flooding. Agro-pastoral fields dissapearigng @ 7.4% per annum. Parks and private spaces at 1.4%. East area fastest dec. Rates of dec effected by social class of inhabitants.
• Water supply -  Current water use is 63 m3/s17 . of this volume only 1.7 m       3/s comes from surviving surface water systems. 42 m3/s fro aquifiers and remaing from Lerma and Catzamala basins. Leakage may -> up to 25%. Recharge replaces roughly 50% per year only. Early in the century Mexico City started sinking due to over-exploitation -> ban on new wells -> stabilisation. A number of areas have been pinpointed for dissemination of contaminants.    Transition zones between hillsides and clay bottom of the basin are highly permeable -> contaminants migrated to aquifiers. Bacteriological, physical, and chem. Monitoring has show dec in quality due to over-extraction of groundwater and extraction of water from formations with high concentrations of certain ions.
• Wastewater treatment – Contemporary wastewater system in Mexico includes several unlined sewer canals, sewers , reservoirs,pumping stations and a deep drainage system – 75% of pop rest use septic tanks.90% of industrial wastes are discharged untreated into domestic waste. 27 treatment plants -> 7% of sewage and then -> irrigation.
• Air Quality – Air pollution problem for over 20 years. Particularly bad in cold season. Mostly from cars. Ozone was highest in 1994,lead was before that in 1986. While unleaded petrol was introduced, the substitute added to the ozone issue – and Mexico is now double what it should b e -> damage to all urban vegetation. In 1994 ozone was at a level considered hazardous for 94 days. Also suspended particles and sulfer dioxide in  industrial parts in central parts carbon monoxide is intense. Also > acid rain and impact on natural areas surrounding the city.
• Centralism and ecological subsidies – Few areas are so far from being self sufficient. Through rapid growth, therefore many issues are exported through system of ecological subsidies -> ie water shortages, contamination. Cost of supplying water to city is enormous. Elevating one cubic meter of water 10 m requires 98 kilojoules of energy plus mechanical efficiency of the system -> For 370 MW are needed -> $900K per day. Transport, water heavily subsidies as are the health side effects of pollution and costs on surrounding forests and crops.
• Sustainability problems and government responses -  Water quality and availability increasingly important issues. The many issues discussed here -> establishment of Sub secretariat of env protection in 1972.  In 1992 there was an explosion in a sewer due to untreated fuel being pumped into pipe. Fed env admin was then split in two –Institute for ecology which would draft legislation and co-ordiate usage and a Env attorney general who would enforce. Also commission for air protection
• Insights for the future – Industrial dev not solely to blame. Centralised govt in place since Aztecs. Has been most densely populated area in world for much of the last two millennia -> political advantage/competitive advantage.