137
Results and Discussion
Spatial Variability of Annual and Monthly Precipitation
The spatial patterns of mean and coefficient of variation (CV %) for the annual
precipitation data from January 1979 to December 2013 at 117 locations are shown
in Fig. 8.2. The lowest values of mean annual precipitation (MAP), less than
434 mm, occur in lowland areas (less than 800 m of altitude) of the state of Durango.
These areas belong to five physiographic sub-provinces: mountains and plains of
Durango, Mapimi Basin, Transverse Ranges, mountains and hills of Aldama and
Rio Grande, and mountains and plains of the North. The highest MAP values in the
state, greater than 1630 mm, occur at highlands (more than 2400 m of altitude).
These areas correspond to two of the physiographic sub-provinces: Durango’s Great
Plateau and Canyons and Southern Plateaus and Canyons. These results show that
elevation affects significantly the precipitation in the study area. A similar distribution of annual precipitation in Durango was reported by Návar (2014) using 80 climatic ground stations.
The degree of rainfall variability can be classified according to CV% (Hare
1983). When CV% < 20 it is considered to have low variability, 30 > CV% > 20
moderately variability, and CV% > 30 is highly variable. Areas with CV > 30% are
also considered vulnerable to drought. Approximately three quarters of the territory
of Durango state have a CV > 30%. Only in the highlands the CV reaches 18–20%.
The five physiographic sub-provinces with the lowest values of MAP also showed
higher variability (CV > 30%). Analysis of the variability of precipitation revealed
that within the arid and semi-arid regions a high interannual variation is characteristic of the arid zones (Kiros et al. 2017). Previous studies established that a
CV > 30% implies a high variation in the rainfall amount and distribution patterns
(Ayanlade et al. 2018). It should be noted that the most populated urban centers in
the study area, Victoria de Durango and Gomez Palacio-Lerdo, are located in areas
with high interannual rainfall variability (CV > 47% and CV > 67%, respectively).
These variability levels are similar to variability record levels reported for the arid
regions with greater climatic variability in the world, such as the northern area of
Australia and Somalia (Van Etten 2009). Interannual rainfall variability is a crucial
component of climate, and can even be a more critical climatic feature than the
long-term average (Thornton et al. 2014). Climate variability has direct impacts on
biophysical and biological systems and can have important repercussions on social
phenomena. Further, to make possible the sustainable utilization of arid lands, land
managers need to be aware of connection between rainfall variability and biotic/
landform responses; for instance, when making decisions about fire management
and surface water storage (Ffolliott 2012; Pandey 2005; Waswa 2012).
Figure 8.3 shows the average of accumulated rainfall per month in the state of
Durango, for the years 1979–2013. The area is characterized by the strong mid to
late summer precipitation maximum in July, August, and September with considerably less precipitation during the rest of the year. Most of the state, except the
8 Spatial and Temporal Analysis of Precipitation and Drought Trends Using…
Results and Discussion
Spatial Variability of Annual and Monthly Precipitation
The spatial patterns of mean and coefficient of variation (CV %) for the annual
precipitation data from January 1979 to December 2013 at 117 locations are shown
in Fig. 8.2. The lowest values of mean annual precipitation (MAP), less than
434 mm, occur in lowland areas (less than 800 m of altitude) of the state of Durango.
These areas belong to five physiographic sub-provinces: mountains and plains of
Durango, Mapimi Basin, Transverse Ranges, mountains and hills of Aldama and
Rio Grande, and mountains and plains of the North. The highest MAP values in the
state, greater than 1630 mm, occur at highlands (more than 2400 m of altitude).
These areas correspond to two of the physiographic sub-provinces: Durango’s Great
Plateau and Canyons and Southern Plateaus and Canyons. These results show that
elevation affects significantly the precipitation in the study area. A similar distribution of annual precipitation in Durango was reported by Návar (2014) using 80 climatic ground stations.
The degree of rainfall variability can be classified according to CV% (Hare
1983). When CV% < 20 it is considered to have low variability, 30 > CV% > 20
moderately variability, and CV% > 30 is highly variable. Areas with CV > 30% are
also considered vulnerable to drought. Approximately three quarters of the territory
of Durango state have a CV > 30%. Only in the highlands the CV reaches 18–20%.
The five physiographic sub-provinces with the lowest values of MAP also showed
higher variability (CV > 30%). Analysis of the variability of precipitation revealed
that within the arid and semi-arid regions a high interannual variation is characteristic of the arid zones (Kiros et al. 2017). Previous studies established that a
CV > 30% implies a high variation in the rainfall amount and distribution patterns
(Ayanlade et al. 2018). It should be noted that the most populated urban centers in
the study area, Victoria de Durango and Gomez Palacio-Lerdo, are located in areas
with high interannual rainfall variability (CV > 47% and CV > 67%, respectively).
These variability levels are similar to variability record levels reported for the arid
regions with greater climatic variability in the world, such as the northern area of
Australia and Somalia (Van Etten 2009). Interannual rainfall variability is a crucial
component of climate, and can even be a more critical climatic feature than the
long-term average (Thornton et al. 2014). Climate variability has direct impacts on
biophysical and biological systems and can have important repercussions on social
phenomena. Further, to make possible the sustainable utilization of arid lands, land
managers need to be aware of connection between rainfall variability and biotic/
landform responses; for instance, when making decisions about fire management
and surface water storage (Ffolliott 2012; Pandey 2005; Waswa 2012).
Figure 8.3 shows the average of accumulated rainfall per month in the state of
Durango, for the years 1979–2013. The area is characterized by the strong mid to
late summer precipitation maximum in July, August, and September with considerably less precipitation during the rest of the year. Most of the state, except the
8 Spatial and Temporal Analysis of Precipitation and Drought Trends Using…