Why does drought occur?
Drought is associated with a climatic phenomenon such as a high anticyclone. At its core, an anticyclone is the formation of an area of high atmospheric pressure. A high anticyclone is warm, characterized by clear weather, lack of precipitation and wind, and low mobility of air masses.
In temperate latitudes, droughts, as a rule, occur in steppes, less often in forest-steppes. According to scientists, drought occurs once every two or three hundred years even in forested areas. In the subtropics and subequatorial zone, droughts occur regularly, since precipitation in such regions occurs only during the rainy season.
What is drought
Drought is a prolonged period of lack of precipitation (rain) and the establishment of constantly high air temperatures. This natural disaster can last from 4-5 weeks to several months. The consequences of drought can become catastrophic.
On our planet, especially in places with an arid climate, drought itself, as well as the hot winds that cause it, are not uncommon phenomena. They cause irreparable damage to agriculture. During a natural disaster, entire crops perished over vast areas, and famine ensued, from which millions of people on the planet died.
Desertification of land and the death of all life on the planet - this is how we can formulate the danger of drought on a global scale.
Types of drought
Depending on where there is an acute lack of moisture, a distinction is made between atmospheric and soil drought. Atmospheric conditions create increased moisture evaporation due to the abundance of sun and reduced air humidity. With soil drought, we are talking about the depletion of the soil due to the lack of rain, due to which the supply of groundwater could be replenished.
If this period lasts for a long time, then lakes, ponds, and small rivers begin to dry up, and then we can already talk about hydrological drought. Depending on the season, drought can be spring, summer, or autumn.
Late summer drought
The third type of drought, characteristic of the Volga region, is late summer. In Saratov, out of 80 years, 43 were characterized by dry weather in July and August. Late summer drought begins during the ripening of winter and early grain crops; by this time they usually have already passed the most critical periods of growth and suffer little from it. Late summer drought has the greatest impact on late crops and the autumn development of winter crops. Late crops shorten the reproductive period due to increased temperature conditions and reduce yield. Sunflower and corn can withstand the July drought relatively easily if they have reached good development and there is still available moisture in the deep layers of the soil. Dry weather during the ripening period of these crops is even a positive factor: sunflower heads and corn cobs are better dried.
Late drought causes especially significant damage to the autumn development of winter crops. The top layers of soil dry out greatly in fallow conditions, which makes it difficult to obtain normal seedlings of winter crops. Sparse, uneven seedlings create unsatisfactory conditions for the harvest from the very beginning.
An example of a late summer drought was 1952. It was preceded by a dry autumn. This affected the autumn development of winter crops and the autumn soil moisture. Due to the strong drying of fallows in many state and collective farms, the seedlings of winter crops were uneven, sparse, and on some crops, especially in the Trans-Volga regions, they appeared only in the spring.
The distribution of snow in the Volga region that year was unusual. In the fields of the Trans-Volga regions, where winters with little or no snow are so common, by the beginning of the spring melting of the snow a thick snow cover had formed, two to three times the average long-term height. A different picture was observed in the right-bank areas, which are usually richer in winter precipitation: there was very little snow there. In the Prikhoper group of districts its height did not exceed 10 cm.
Water losses due to spring runoff in fields deeply plowed in the fall turned out to be very insignificant. The spring runoff was fed mainly by water flowing from unplowed fields, fallow lands, pastures, as well as by large amounts of snow collected in ravines and ravines.
A characteristic feature of spring soil moisture was great diversity in the depth of wetting, which was determined by the uneven distribution of snow in the fields. In the same field, along with deeply moistened places, there were also those where the depth of soil wetting did not exceed 40-50 cm.
In the spring, from the first days of field work, mild weather set in with moderate temperatures and periodic precipitation, mainly of a rainy nature. They were distributed very unevenly.
A sharp increase in air temperature began in the third decade of June, when the average air temperature over the decade exceeded the long-term average for this period in some areas by 6-7°, and the maximum temperature rose to 37° or more. After a short cold snap in early July, dry, hot weather settled in for a long time.
Moderately warm and humid spring weather favored the spring regrowth of winter crops. Their unsatisfactory autumn development was somewhat improved by additional spring tillering of plants and new shoots, where there were none in the fall due to dry soil. But still, in most regions of the Volga region, winter crops were sparse, which, along with dry weather during grain loading, negatively affected their yield.
Spring wheat and other early grain crops developed very well. However, their harvest suffered to some extent from hot weather with a large number of dry days during grain filling, especially in areas with insufficient spring soil moisture.
Under the conditions of the late summer drought of 1952, the production crops of the elite seed farm of the Research Institute of Agriculture of the South-East produced 15.5 winter rye, 16.2 winter wheat, 14.3 spring wheat, 7 millet, 3.4 sunflower, corn - 3.9 centners per hectare. The harvest of late crops this year was 3-5 times less than winter and early grain crops.
On late crop crops, the negative impact of late summer drought can be mitigated by preserving soil moisture through careful cultivation of row spacing. Proper processing of black fallow and the use of small cultivations with tools with knife-shaped working bodies, and, if necessary, with rolling, allows moisture to be retained in the top layer of soil, even in dry years, ensuring normal germination of winter crops. This emphasizes the special importance of clean vapors for the arid zone.
How dangerous is drought?
During a period of drought, the flow of water to the root system of plants stops, the moisture consumption exceeds its influx, the water saturation of plant tissues critically decreases, and the normal conditions of its growth are disrupted. Spring drought can destroy early grain crops, summer drought harms fruit plants, early and late grains; autumn drought destroys winter crops.
Drought can lead to ignitions and long-lasting fires in steppes or forests, as well as to peat fires, which entail extremely dangerous smoke for the body.
Drought is detrimental to people. According to statistics, more than a million people have died from droughts in Africa over forty years. The UN even established World Drought Day – it is celebrated on June 17th.
Causes and types
So, drought is a long period (it can last from several weeks to 2-3 or more months) of stable weather with abnormally high air temperatures for a given area and extremely little precipitation. Droughts occur when high pressure (anticyclone) remains in the atmosphere for a long time and downward atmospheric flows prevent rain from occurring.
The abundance of solar heat and gradually decreasing air humidity lead to increased evaporation - the so-called atmospheric drought. As a result, the moisture reserves in the soil are depleted without replenishment by rainwater, causing soil drought. Gradually, as it develops, ponds, lakes, springs and even rivers dry up. Hydrological drought begins
Heat and lack of precipitation are indispensable companions of drought
There is also the concept of physiological drought , when it is difficult for water to enter plants through their root system. The plant spends more moisture on evaporation than it receives from the soil. Tissues begin to experience water deficiency, which negatively affects photosynthesis processes. This is due to the fact that in the spring, at significant daytime temperatures, the soil is still quite cold and this does not allow the plant to feed normally even if it contains the required amount of water and minerals.
Depending on the season, droughts are divided into spring, summer and autumn. In the driest years, drought may well move from one season to another, becoming, for example, spring-summer or summer-autumn. At times, under particularly unfavorable conditions, starting in the spring, it may well last until late autumn.
Droughts are almost always accompanied by dust storms and dry winds, which further increase the evaporation of moisture from the surface of the earth.
Of course, nowadays, in most cases, droughts no longer have such dire consequences as in past centuries. But they still require significant financial costs to preserve and protect the crop.
In Russia, the drought of 2010 destroyed crops on an area of 9.5 million hectares
The fight against droughts consists mainly of accumulating and preserving moisture in the soil. To do this, snow retention is carried out, forest shelterbelts are created that protect arable lands from the winds, ponds and reservoirs are created in gullies and ravines, soils are harrowed, etc.
How to deal with drought?
Measurements of moisture reserves in the soil and accurate calculations of the volume of snow cover help predict the likelihood of drought. For example, if the moisture reserve in a meter layer of soil in autumn does not exceed 50% of the average annual level, or the thickness of snow does not reach half the average for a long-term measurement period, then the risk of drought is very high. This means that protective measures should be taken.
To prevent drought, a number of actions are taken to retain moisture in the soil and retain snow on the fields. The land is plowed deeply, transverse plowing is carried out on the slopes, and the microrelief of the surface of the arable land is changed. It is especially important to do this on high-density soils.
With the help of ploughing, harrowing, and cultivation, they try to maintain the soil in a loose state. Timely feeding of fertilizers, regulation of snow melting processes, and accelerated pre-sowing soil preparation help maintain the viability of plants.
An effective way is to combine sowing of different types of crops that require different amounts of rainfall at certain times of the year. For example, winter crops are resistant to summer droughts, but need moisture in the fall; early spring crops, on the contrary, require special moisture in the first half of summer. Agronomists also grow special drought-resistant varieties of various crops.
Causes of drought
Drought usually occurs when changing weather conditions disrupt the water cycle. Changes in the direction of winds can significantly affect the amount of rainfall that a region receives. But lack of precipitation does not necessarily lead to drought. Drought is the result of a combination of factors. The connection between climate change, Arctic ice loss and extreme weather events is currently an area of active research in the scientific community. However, it is clear that there are natural weather cycles that lead to drier periods and wetter periods.
El Niño and La Niña
Scientists have found a connection between some climate phenomena and drought. El Niño is a meteorological phenomenon associated with an increase in the temperature of the surface layer of water in the Pacific Ocean along the central South American coast. This phenomenon is causing drought in Indonesia, Australia and northeastern South America.
La Niña is the “opposite” of El Niño, which cools surface waters in the Pacific Ocean along the coast of South America. Cooler waters influence hurricanes, contributing to harsher-than-normal conditions in the Americas. El Niño and La Niña usually last about a year. La Niña's impact on weather patterns is often more complex than El Niño. Two of the most destructive droughts in United States history—the Dust Bowl of the 1930s and the 1988 drought in the Midwest—are associated with La Niña effects.
There is still a lot of discussion about the connection between drought and global warming, the current period of climate change. A 2013 NASA study predicted that warmer temperatures worldwide would mean more rainfall in some parts of the world and less rainfall in others, leading to more flooding and more drought worldwide. Other scientists doubt that there will be more droughts and believe that global warming will instead contribute to a wet climate around the world.
Although drought is a natural phenomenon, human activities can make it worse. For example, drought may become more severe if it occurs in an area with high water demand and where water management is poor. But even when there is no rainfall, drought may not occur and can be prevented if there is sufficient water (for example, in reservoirs) and prudent management of water consumption.
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Types
People tend to define drought in three main ways:
- Meteorological drought occurs when there is less than average rainfall over an extended period of time. Meteorological drought usually precedes other types of drought.
- Agricultural droughts affect crop yields or habitat ecology. This condition can also occur independently of any change in precipitation levels when either increased irrigation or soil conditions, as well as erosion caused by poorly planned agricultural efforts, cause a shortage of water available for crops. However, in a traditional drought, it is caused by a prolonged period of below-average rainfall.
- Hydrological drought occurs when water supplies in sources such as aquifers, lakes and reservoirs fall below a locally significant threshold. Hydrological drought tends to occur more slowly because it involves stored water that is used but not replenished. Like agricultural drought, it can be caused by more than just precipitation. For example, around 2007, the World Bank awarded Kazakhstan a large sum of money to restore water that had been diverted to other countries from the Aral Sea under Soviet rule. Such circumstances also put their largest lake, Balkhash, at risk of drying up completely.
As the drought continues, conditions around it gradually worsen and its impact on the local population gradually intensifies.
