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Spatial Patterns of Drought Frequency
Since droughts vary in time and space, the regional distribution of drought using
drought events with SPI-12 values less than −1.0 was interpolated and mapped for
12 months in a year. This value of SPI is typically chosen as an indicator of drought.
In some regions, a good rainfall in one particular month can create the impression
that the drought is over, but until the SPIs are not above a particular value at all
scales (typically −1), a drought will still affect a region in one way or another (Patel
et al. 2007).
We calculated the drought event for each location in the state of Durango and
interpolated the spatial distribution of the drought events (Fig. 8.5). More than half
of the state experienced 53 or more droughts during the period of analysis of
35 years. SPI field station calculations in the ground station (Rivera del Río et al.
2007) recorded an average of 15 dry periods in 14 years. There is a certain proportion of SPI drought events detected with ground field measurements and with satellite precipitation. The station (−104.38, 22.63) in the municipality of Mezquital
registered fewer drought events (14), whereas the location (−105.63, 25.13) in
Tepehuanes presented the most (74) drought events. The average of drought events
in all stations was 54.
The spatial distribution of frequency droughts events for the first 5 months was
similar. At this time of year, there are slightly more droughts in the east and a small
portion of the northeast of the study area. In the east, these areas include much of
Chihuahua’s and Durango’s Great Plateau and Canyons and the northern portion of
Southern Plateaus and Canyons physiographic sub-provinces. And in the north part,
some areas of Mapimí Basin. By June, an increase in the frequency of drought
events throughout the state of Durango was noticeable. At the beginning of the rainy
season (July), the frequency drought events decrease in the study area and in this
month the droughts are more frequents in the east part. This area covers the following physiographic sub-provinces, the eastern part of Mapimí Basin, the huge portion of Transverse Ranges, mountains and hills of Aldama and Rio Grande,
mountains and plains of the North, and small portion in the south of the mountains
and plains of Durango. However, at the end of the rainy season (September) the
frequency of drought events increased throughout the state. October, November,
and December have a similar spatial trend in the frequency of droughts, and during
these months there are more incidences towards Mapimi basin, Transverse Ranges,
mountains and hills of Aldama and Rio Grande and central part of Durango’s Great
Plateau and Canyons and mountains plains of Durango.
It is important to note that in the previous section, June and September showed
many areas with increases in precipitation. Instead, this section indicates these
months have large regions of frequents droughts, which seems to be contradictory.
It is because the SPI for a particular month is calculated considering the accumulated rainfall from previous months, depending on the timescale used. In this case,
although September and June have shown increases in precipitation, the index contemplates the decrease in rainfall that has occurred in previous months which has
more intensity than the increases.
8 Spatial and Temporal Analysis of Precipitation and Drought Trends Using…
Spatial Patterns of Drought Frequency
Since droughts vary in time and space, the regional distribution of drought using
drought events with SPI-12 values less than −1.0 was interpolated and mapped for
12 months in a year. This value of SPI is typically chosen as an indicator of drought.
In some regions, a good rainfall in one particular month can create the impression
that the drought is over, but until the SPIs are not above a particular value at all
scales (typically −1), a drought will still affect a region in one way or another (Patel
et al. 2007).
We calculated the drought event for each location in the state of Durango and
interpolated the spatial distribution of the drought events (Fig. 8.5). More than half
of the state experienced 53 or more droughts during the period of analysis of
35 years. SPI field station calculations in the ground station (Rivera del Río et al.
2007) recorded an average of 15 dry periods in 14 years. There is a certain proportion of SPI drought events detected with ground field measurements and with satellite precipitation. The station (−104.38, 22.63) in the municipality of Mezquital
registered fewer drought events (14), whereas the location (−105.63, 25.13) in
Tepehuanes presented the most (74) drought events. The average of drought events
in all stations was 54.
The spatial distribution of frequency droughts events for the first 5 months was
similar. At this time of year, there are slightly more droughts in the east and a small
portion of the northeast of the study area. In the east, these areas include much of
Chihuahua’s and Durango’s Great Plateau and Canyons and the northern portion of
Southern Plateaus and Canyons physiographic sub-provinces. And in the north part,
some areas of Mapimí Basin. By June, an increase in the frequency of drought
events throughout the state of Durango was noticeable. At the beginning of the rainy
season (July), the frequency drought events decrease in the study area and in this
month the droughts are more frequents in the east part. This area covers the following physiographic sub-provinces, the eastern part of Mapimí Basin, the huge portion of Transverse Ranges, mountains and hills of Aldama and Rio Grande,
mountains and plains of the North, and small portion in the south of the mountains
and plains of Durango. However, at the end of the rainy season (September) the
frequency of drought events increased throughout the state. October, November,
and December have a similar spatial trend in the frequency of droughts, and during
these months there are more incidences towards Mapimi basin, Transverse Ranges,
mountains and hills of Aldama and Rio Grande and central part of Durango’s Great
Plateau and Canyons and mountains plains of Durango.
It is important to note that in the previous section, June and September showed
many areas with increases in precipitation. Instead, this section indicates these
months have large regions of frequents droughts, which seems to be contradictory.
It is because the SPI for a particular month is calculated considering the accumulated rainfall from previous months, depending on the timescale used. In this case,
although September and June have shown increases in precipitation, the index contemplates the decrease in rainfall that has occurred in previous months which has
more intensity than the increases.
8 Spatial and Temporal Analysis of Precipitation and Drought Trends Using…