By Cecilia Conde, CiudadUniversitaria, Mexico; and Carlos Gay, Instituto Nacional de Ecologia, M�xico

Within Phase I of the "Country Study: Mexico" (1994 - 1996), the vulnerability of Mexico was studied under climate change conditions considering seven research areas: Forestry, Desertification and Drought , Human Settlements, Energy and Industry, Agriculture, Hydrology and Coastal Zones.

Except for the Coastal Zones study, climate change scenarios were constructed using arbitrary incremental and temperature/precipitation anomalies obtained from two General Circulation Models: CCCM and GFDL. Regional climate change scenarios were also generated for Mexico based on statistical downscaling techniques applied to GCM output from 2´ CO₂ experiments. Results indicate that Mexico will experience less or normal summer precipitation and increased precipitation during winter.

General results of the vulnerability studies pointed to the following regions as being the most vulnerable:

• Central and Lerma-Chapala-Santiago Basin: According to the results of the Hydrology study, the current critical conditions observed in the base scenarios for these regions may be aggravated. The predicted increase in temperature coupled with a decrease in rainfall could result in severe water supply shortages in these regions, exacerbated by the growth in population and industries predicted by the Human Settlements research.
• Northern areas and regions with large populations, especially in Central Mexico, are most vulnerable to droughts and desertification, since erosion and drought severity will increase with higher temperatures and rainfall variations in these arid and semi arid regions.
• The Tabasco State Coast will be most vulnerable to sea level changes. Approximately 40 to 50 km of inland sea penetration is predicted by the Coastal Zones studies, using the trends observed in 50 years of aerial photograph data, and with 0.5 meters per decade as a change scenario.
• Northern and Central regions are most vulnerable in the agricultural sector, according to application of a crop simulation model (CERES maize), and calculation of the possible changes in the aptitude for maize optimal production, given different temperature and precipitation changes.
• Forests in temperate climates will be the most vulnerable ecosystems, particularly those located on the Eje Neovolcanico (Neovolcanic Axis mountain range) and Northern regions of the country, (dependent of altitude).
• The maximum vulnerability is anticipated in the Central regions of the country, according to the Human Settlements studies, which show major increases in population growth, density, morbidity, and decrease in water supply.
• Energy and Industry studies found that the most vulnerable regions in this sector will be the Central and Northern regions of the country and the Tabasco Coasts.

Given these results, the three Mexican regions most vulnerable to climate change are, in order of importance: Central, Northern and Tabasco Coast.

In a second phase of the Mexican assessment, two states were taken as Case Studies: Tlaxcala (central region) and Sonora (northern region). For those states, vulnerability and adaptation strategies are being analyzed, considering also the historic impacts under El Niño and La Niña conditions.

The Tlaxcala Case Study is being developed in the project entitled On the use of climate forecasts for agricultural activities in the State of Tlaxcala, México. The economy of this state is highly dependent on rain-fed corn production. Population growth, erosion and drought are also acute problems in this state. Producers and state managers are participating in this project.

For the Sonora studies, the project entitled Climate Variability and Its Potential Impact on Transboundary Freshwater Resources in North America was developed, in cooperation with the University of Arizona.

Various studies have shown that the El Niño/Southern Oscillation phenomenon mainly affects precipitation and moisture conditions over Mexico. The ENSO signal may explain up to 25% of the variability in monthly precipitation in some parts of Mexico, particularly along the northern Mexican states. The ENSO impacts are summarized in Table 1.

During some El Niño years, winter precipitation may be so great that streamflow and water levels in dams may exceed those observed during summer. In contrast, summer droughts during these events can lead to serious deficits in reservoir levels and in rain-fed maize production. In Mexico during 1997, the estimated costs of climate anomalies associated with El Niño were around 8 billion pesos (900 million US dollars), particularly in agricultural activities, when 2 million hectares were affected by a severe drought.

In the State of Tlaxcala, various climatic regimes are found, in relation to complex topography and major differences in land use from one place to another. On an interannual basis, the climate of Tlaxcala is essentially regulated by large- scale atmospheric circulation, such as those observed during El Niño events. This variability strongly affects maize production.

During the Tlaxcala regional study, the cooperation of producers (organized in the PRODUCE A.C. Foundation) and state government officials was crucial. Through periodic discussions, climate products were delivered as useful information to plan agricultural activities and this was also a way to analyze adaptation strategies. The CERES maize model, which included information obtained from farmers, was also used to examine impacts and adaptation to drought in the Tlaxcala region. The positive experience with the use of seasonal climate forecasts in 1998 convinced producers in the state to repeat the analysis in 1999.

For more information, contact

Cecilia Conde, Centro de Ciencias de la Atmósfera, UNAM.Ciudad Universitaria; Circuito Exterior 04510; México, D.F. México; e-mail: conde@servidor.unam.mx; or Carlos Gay, Instituto Nacional de Ecologia, Secretaria de Medio, Ambiente Recursos Naturales y Pesca; México, D.F. México; e-mail: cgay@chajul.ine.gob.mx