The climatological records for ten (10) stations located in Baja California, in the vicinity of the Ojos Negros valley,
were analyzed to establish drought intensity-duration-frequency relations.
The results of the analysis are shown in Table 6.
While the average drought intensity for all stations is 0.83 (moderate), the intensity at Ojos Negros is 1.23 (severe).
This shows that drought intensity is likely to be severe in the immediate vicinity of the Ojos Negros valley, while
remaining moderate for the rest of the study region. When the data is taken all together, 48% of the drought events
are moderate (intensity less than 0.625), 34% are severe (intensity between 0.625 and 1.25), and 18% are extreme (intensity greater than 1.25).
Average drought duration is 2 yr at Ojos Negros, and 2.46 yr for the region.
Average drought frequency is 3.54 yr at Ojos Negros, and 3.96 yr for the region.
It is concluded that droughts in the Ojos Negros valley and vicinity are likely to be moderate to severe, to recur every 4 yr, and to last about 2 yr.
Strategies for coping with droughts in the Ojos Negros valley include drought preparedness and mitigation.
The following strategies have been identified:
5.1 Herd management
In principle, herd numbers should be related to the climate. The local climate is subject to variability, and the dry periods
(droughts) may last more than one year. In the Ojos Negros valley in particular, drought is likely to be moderate to severe,
last 2 yr, and recur every 4 yr. Therefore, ranchers must consider this climatic constraint
when planning the size of their herds. In general, herds should expand during
periods of wet weather, and contract during drought periods. Forecasting the climate on an annual basis is the responsibility
of the national water agency.
During a drought, the herd manager should evaluate the members of the herd to eliminate the inefficient individuals.
The herd size should be reduced to a number that can be supported by the available resources.
The physical attributes of the individual animals should be evaluated critically.
Animals with bad physical attributes or diminished reproduction ability should be considered for culling.
The replacement heifer crop should be critically evaluated.
In a drought year, the minimum number of heifers should be retained, and the rest should be sold.
Bull should be evaluated to select those that are getting old and in need of replacement.
Old bulls should be eliminated during drought years, and replaced as soon as practicable.
All cattle are affected by a host of internal and external parasites. Cattle under nutritional
and heat stress are less resistant to parasites than under normal conditions.
Strategic deworming during a drought will relieve some of the nutritional stress on the animals.
Heifers and calves are not able to compete with mature cattle for pasture or supplemental feed.
Drought feed is costly and it is important to feed only those animals who really need it.
Segregating animals gives each class a better chance of getting needed feed supplies.
Vulnerable classes can be segregated and given preferential treatment.
The older dry cows can be moved to the poorer forage fields.
Contract grazing or renting pasture is another drought strategy.
However, the cost of hauling or renting the pasture should not be more than the cost of purchasing feed.
Use of a drought-affected paddock can be optimized by providing local water facilities and supplemental hand feeding.
5.2 Conservation practices
Water retention and detention structures capture storm-water runoff which can be used
for a variety of purposes, including groundwater recharge, irrigation, and drinking water
Windbreaks and shelterbelts help in reducing wind velocity and, therefore,
evaporation and evapotranspiration, aiding in coping with drought.
Rainwater harvesting can be accomplished for immediate or eventual use in irrigation or drinking water for livestock.
Landscape contouring and terracing can be implemented where feasible to reduce runoff and direct excess moisture
into areas planted with trees, shrubs, and grass.
5.3 Interviews with local actors
During June 2002, several interviews were performed with local cattle ranchers.
The interviews sought to collect perceptions about drought, drought characteristics,
and drought mitigation, to serve as a basis for the development of policy.
Most people interviewed said that rain appears to have have been steadily decreasing.
Some ranchers observed that in the 1950's it rained all-year round and
the pastures were always green.
Since the 1970's, drought appears to have intensified.
Rain was plentiful in 1978, 1981, 1992 and 1998.
In other years, rain has been limited, and some years have not had any rain.
Ranchers do not consult outside sources (i.e., weather agencies) to learn whether is it going to rain or not.
They feel reluctant to ask these sources because they feel they could be wrong.
The ranchers agree that there is a recurrence interval between the drought years
and the rainy years, but the periodicity of the cycle is unknown. Some say the rainy periods
last from 4 to 7 yr, while the drought periods last from 2 to 4 yr. Yet others
believe that drought recurs every 4 yr on the average.
Furthermore, there are those that believe that even years are rainy while odd years are dry.
During drought years, there is not enough moisture for normal dryland pasture growth.
Irrigation is an option for those that can rely on groundwater, and this is typically the case of
Ojos Negros; but those ranchers which have no wells or small wells are significantly affected by drought.
Herd reduction to 50% or less is a common strategy to cope with drought. Some ranchers move their cattle to
rented land, while others are forced to purchase hay to feed their lot.
The last resort is to undersell the herd, with consequent loss of profitability.
When selecting the cattle to be sold or removed, farmers usually go first for the older animals,
then they separate the newborn herd to reduce competition for food.
Other drought related effects are fires, erosion and groundwater depletion.
The Comisión Nacional del Agua (National Water Commission) has supplied farmers with statistical facts,
seminars and some additional help. SAGARPA and other government agencies have subsidized the shipping of hay from Mexicali to Ojos Negros
Retention walls, or structures such as dykes or dams, as well as natural obstructions to runoff
are yet to be used to retain precious water during drought.
Water reservoirs are an option, but water would be retained only for a limited amount of time.
Most ranchers believe that it is important to ration the water supply;
otherwise, the valley is going to eventually lose its economic potential.