Geoscience Reference
In-Depth Information
The international practice aims at a comprehensive approach to flood management in
response not only to the consequences of a specific event, but measures that starting from
the prediction of extreme events and monitoring for early warning purposes to
establishment of civil protection measures for those affected by the occurrence of such
events and the hazard remediation, including infrastructure development and non-
structural measures to reduce the vulnerability.
The structure of this work is as follows. Section 2 presents the summer precipitation regime
over Mexico Valley. Section 3 a brief description the meteorological radar deployed in Cerro
Catedral at western of Mexico Valley. In Section 4 a case study for the microwatershed of the
Mixcoac River is discussed. In Section 5 new design of a weather information system is
proposed. Concluding remarks are found in Section 6.
2. Mexico valley precipitation climatology
The México Valley is located at 2240 m altitude and at a latitude of approximately 19°N and
is characterized by well-defined rainy season from late May to early October which can be
classified as a monsoon climate type.
The orography of region plays an important role on the precipitation patterns (intensity,
timing, spatial distribution and, extreme events occurrence). On northeastern area, region
nearly flat, the average precipitation is around 500 mm/year and at southwestern
mountainous region part of the México Valley, the average reaches almost 1200 mm/year (Fig.
1). The occurrence of extreme events follows the same patterns as shown by Magaña et al.
(2003) by establishing a criterion to determine when intense precipitation should be considered
an extreme event based on a Gamma distribution of the observed amount of daily rainfall, for
each station of the rain gauge network (Fig. 2). The similarity of spatial variability of severe
weather and average precipitation becomes apparent. An extreme precipitation event to occur
in the western or southern part of the basin, rainfall in 24 hours should exceed 25 or 30 mm,
while in the eastern part of the city, more than 15 mm in 24 hours already constitute an
extreme event. To a large extent the interaction of the mountains with the summer easterly
winds determines, the characteristics of precipitation (Barros 1994).
The summer precipitation diurnal cycle indicates the intense precipitation begins in the
afternoon (Fig. 3), around 16:00 h local time, generally in the eastern part of the valley, and
propagate to the western part during the evening, reaching the other extreme of the valley
by late evening and midnight (Mendez et al., 2006).
3. The Cerro Catedral radar
The radar network operated by Mexico's National Water Commission is focalized mainly in
monitoring of the tropical cyclone activity and consists of thirteen C-band radars
(manufactured by Ericsson Inc., Enterprise Electronics Corporation and Vaisala). There is
also a weather radar deployed at Cerro Catedral which cover almost all Mexico Basin
(located 40 km and altitude 3785 m, approximately 1500 meter above México City), to
monitor severe weather over this region (Fig. 4). This radar measures reflectivity and has a
Doppler and dual polarization and, is configured as follows (Table 1):
