Agricultural Drought in North-Central Mexico - Monitoring and Predicting Agricultural Drought: A Global Study - page 139

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process of data transfer from manual stations to the SMN, so that drought
monitoring can be performed on real-time basis. The automation process is
being accomplished using 74 automatic stations distributed all over Mexico
since 1999. In the five states there are nine stations, six of them located at
the mountainous southwestern part of Chihuahua, two in Durango, and
one in Zacatecas. For the study of drought it would be better to install
such stations at the desertic zones of the arid states (e.g., eastern part of
Chihuahua).

W eather Variables

In Mexico, only a few weather variables are monitored daily at the man-
ual stations. These variables include precipitation (24-h total), maximum
and minimum temperature, evaporation, wind speed and direction. The
new automatic stations linked via satellite (GOES-12) monitor the above
variables plus relative humidity, solar radiation, and precipitation. Mean
values of 10-min data are sent every3htotheSMNheadquarters for rapid
uploading on-line (http://smn.cna.gob.mx/productos/emas/emas.html).
Some of the common drought indices, such as the Palmer drought sever-
ity index (Palmer, 1965) require data on evapotranspiration, recharge,
runoff, soil moisture characteristics, and so on, in addition to precipita-
tion and temperature (Lohani and Loganathan, 1997). It would therefore
be appropriate to monitor some additional variables, at least at limited
number of stations.

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C onclusions
Droughts have far reaching social, economic, and political implications.
With limited hydrometeorological data available in Mexico, simple
drought indicators such as the deviation from the mean rainfall are more
suitable than a sophisticated indicator such as Palmer drought severity in-
dex. The standardized precipitation index, which depends only on precip-
itation, appears to be a qualitative tool for drought monitoring, but this
index was not suitable for quantitative assessment of agricultural droughts
at small scales. The correlation between maize and bean yields with SPI
ranged from 0.26 to 0.54. However, the relationship was better in the case
of bean than maize. Additional factors that influence crop yields were not
analyzed. Low yields of maize and high probabilities of drought occur-
rence in the north-central states tend to discourage maize farming in these
areas. However, bean is a less drought-resistant crop and therefore is more
favorable for the region.
Drought research in Mexico is a relatively new but is catching up fast.
New models and methodologies are being attempted to better understand
the climatic processes responsible for drought occurrence. Currently, meth-
odologies can estimate length, severity (intensity), and spatial distribution