Droughts are major natural disasters for many parts of the world (Maybank, Bonsai et al. 1995). Droughts are most common when typical weather patterns are disrupted, leading the water cycle to be disrupted. Droughts are characterized by a decrease in precipitation over a lengthy period, such as a season or a year, and can occur in virtually all climatic zones, including both high and low rainfall locations (Orimoloye, Belle et al. 2022). According to a report by the IPCC, the average global and ocean land surface temperature increased by 0.85 degrees Celsius between 1880 and 2012 (Orimoloye, Belle et al. 2022).
Cause of Drought:
The causes of drought are either natural or manmade or both. A lack of precipitation is the major forcing factor for a drought. The interannual variability of precipitation and to a lesser extent temperature, affect the frequency and intensity of droughts. This variability is the result of a number of factors that
force the climate system and operate over a range of time and space scales (Maybank, Bonsai et al. 1995). Scientific investigations have revealed that the primary cause is the fluctuation of the general atmospheric circulation. As a consequence of such fluctuations the rain-producing components have been weakened or dislocated during drought years. Human interferences such as deforestation, overgrazing and over cultivation enhance the severity and prolongation of drought recurrences (Haile 1988) .
Types of Drought:
Drought are classified it as typically affecting an area of a million square kilometers and having a duration of weeks or months by Newark (1982) (Maybank, Bonsai et al. 1995). Drought indices can show the weakness and intensity of different types of droughts separately, but in recent years, certain indices have been introduced for indicating the intensity and weakness of the various types of droughts together, in a single series. Among the most important of these indices, the multivariate standard precipitation index (MSPI) and joint deficit index (JDI) can be pointed out. These indices combine some series of standard precipitation indices (SPI) that each of them indicates a certain type of drought (Aghelpour, Mohammadi et al. 2020).
Using the Standardized Precipitation Index (SPI), as the indicator, a functional and quantitative definition of drought can be established for each time scale. A drought event for time scale i is defined here as a period in which the SPI is continuously negative and the SPI reaches a value of -1.0 or less. The drought begins when the SPI first falls below zero and ends with the positive value of SPI following a value of -1.0 or less(McKee, Doesken et al. 1993). Drought intensity is arbitrarily defined for values of the SPI with the following categories:
Table 1 Classification of the SPI’s values and corresponding probability limit (Aghelpour, Mohammadi et al. 2020), (Bazrafshan, Hejabi et al. 2014), (Rahimi, Ebrahimpour et al. 2013)
The SPI calculated in this way has the following desirable traits (McKee, Doesken et al. 1993):
- The SPI is uniquely related to probability.
- The precipitation used in SPI can be used to calculate the precipitation deficit for the current period.
- The precipitation used in SPI can be used to calculate the current percent of average precipitation for time period of i months.
- The SPI is normally distributed so it can be used to monitor wet as well as dry periods.
- SPI can be calculated for the other water variables of snowpack, reservoir, streamflow, soil moisture, and ground water
- The SPI is normalized so that wetter and drier climates will be represented in a similar way.
Generally, forecasting some different types of drought together (e.g., meteorological, hydrological and agricultural droughts simultaneously) by the current method is a “theoretical study” and to be changed to an “applied study”, it is suggested to validate the indices by the actual simultaneous events of these different drought types (Aghelpour, Mohammadi et al. 2020).
Measurement of Drought or Drought Monitoring and Evaluation:
Remote sensing information can be used to assess and monitor drought features because it provides real-time geographic observations of many atmospheric and land surface variables that can be utilized to estimate precipitation, evapotranspiration, and soil moisture and vegetation conditions. Traditional drought monitoring and evaluation approaches rely on rainfall data, which are scarce in some regions, frequently erroneous, and, most crucially, impossible to gather in near-real time. The data from satellite sensors, on the other hand, are always available and may be used to predict the beginning of drought, as well as its duration and magnitude (Orimoloye, Belle et al. 2022).
Drought as Disaster:
It might be difficult to identify the beginnings of a drought. Unlike many natural disasters that have immediate and spectacular consequences, such as earthquakes, tornadoes and hurricanes, drought can develop gradually and subtly. Droughts develop slowly, and until human activity begins to be affected by an on-going reduction of precipitation, their existence is unrecognized (Maybank, Bonsai et al. 1995). Droughts have been identified as an environmental hazard by environmentalists, ecologists, hydrologists, meteorologists, geologists, and agricultural expert (Orimoloye, Belle et al. 2022).
Drought impacts are classified in three major categories:
- Social Impacts
- Environmental Impacts
- Economic Impacts
Table 2 Drought impacts (Adopted from (Orimoloye, Belle et al. 2022)
|S. N.||Drought Impacts||Discussion|
|As a result of the grave threat posed by drought, the United Nations
estimates that millions of people in drought-prone areas of Sub-Saharan
Africa would be compelled to migrate to North Africa or Europe in the
next few decades. It has an impact on various habitats, such as
savannahs, in addition to dry regions. Forced migration can occur due to
a variety of factors. It frequently occurs as a result of life-threatening
circumstances, such as crisis or famine, due to drought episodes
|Poverty and unemployment||For example, in the Western Cape province affected by drought recently,
the tourism industry in the province suffered as a result of the drought.
The number of tourists visiting the province decreased during the drought, even though the impact has yet to be quantified. This was
reflected in the fact that the number of overnight guests in the region
increased by only 1% year over the year from 2016 to 2017, compared to 7% a year earlier. Bookings at some hotels decreased by 10% to 15% in 2018 compared to 2017. Tourism is anticipated to employ almost 300,000 people in the Western Cape, of which a large number of them have been relieved of their jobs.
|Overstocking and reduced quality of living||Drought can affect human health, result in conflicts and impact our quality of life. Increased dust levels due to drought occurrence could be harmful to persons with respiratory issues, and wildfires sparked by the drought could pose a public safety risk. Farmers and individuals whose livelihoods are inextricably linked to land and water are more likely to be stressed, anxious or depressed.|
|Reduced or no income||Changing climate patterns, particularly droughts, have a negative impact on farmers and can result in food insecurity. As a result, farmers’ and their families’ incomes decline, pushing them deeper into poverty.|
|Malnutrition and famine, and civil strife and conflict||The drought’s economic and health effects have pushed millions of people deeper into poverty and suffering. Drought’s secondary effects
are still being felt by children and their communities across Africa. This means fewer employment prospects, reduced livelihoods, lower economic output and restricted access to basic food and services.
|Social unrest and distrust||The key causes that have aggravated the problem of food production, distribution, and access are drought and conflict. Within an already
tough setting of fragile ecosystems, high rates of population increase and poverty have also played a role. Because about 80% of the population in the region lives in rural areas and relies almost entirely on agriculture for food and income, solutions to poverty and food insecurity must be found primarily in the agricultural sector.
|Increased threat to human and animal life||Drought has a variety of effects on humans and animals. Plants and animals, similar to humans, rely on water. When there is a drought, their food source may be reduced, and their habitat may be harmed; South Africa is not excepted from these impacts.|
|Social pressure and reduced safety||Drought has the potential to affect people’s health and safety.
Drought-related effects on society include anxiety or depression over economic losses due to drought, conflicts when there is insufficient water, reduced incomes, fewer recreational activities, increased heat stroke incidences and even human death.
|Loss of biodiversity||Drought conditions can also significantly enhance the risk of wildfire.
Plants and trees wither and die as a result of a lack of water, increased bug infestations and diseases, all of which are linked to drought, as they become fuel for wildfires. Long periods of drought can lead to more and more destructive wildfires, which have a wide range of consequences for the economy, the environment and society, including the destruction of neighborhoods, crops and habitats.
|Environmental degradation||Drought can cause lower water levels in reservoirs, lakes and ponds, as well as decreased river flow. This reduction in accessible water may
result in the loss of some wetlands, groundwater depletion and even
water quality issues (e.g., salt concentration can increase due to drought episodes). Inadequate water supply can lead to soils that are unable to support crops, increased dust owing to drought and erosion and a higher risk of wildfires due to the dry climate.
|Reduced income and food shortages||Drought is one of the causes of malnutrition and hunger, as it affects agricultural production, resulting in food insecurity in South Africa.
Drought is the primary cause of global grain output shortages relative to consumption in the first half of the twenty-first century, posing a threat to food security. The 2015–2016 drought event (attributed to a strong El
Niño) in southern Africa further highlighted its vulnerability to climate-related regional food insecurity.
|Lower accessibility to water||Droughts aggravate water scarcity, putting people’s health and productivity at risk. A crucial climate change mitigation strategy for the coming years is to ensure that everyone has access to sustainable water
and sanitation services. Fish, animals and plant life can be harmed by a lack of water and soil’s inability to grow crops. Plant growth may be
hampered by poor soil quality and insufficient water, and animals may
not have enough to drink. There may also be a risk of endangered species becoming stressed, as well as a loss of biodiversity in the affected area.
|Plant and vegetation scorching||Animals and plant life can be impacted by a lack of water and soil’s inability to grow crops. Plant growth may be hampered by poor soil
quality and insufficient water due to drought, and animals may not have enough to drink. There may also be a risk of endangered species
becoming stressed, as well as a loss of biodiversity in the affected area. It might take years for many woody plants and vegetation to show
detrimental long-term impacts after a drought. A single drought event
may cause leaf scorch. If the drought persists, the entire leaf will perish.
Stem dieback, which is caused by the loss of tiny feeder roots, is a common long-term impact of drought.
|Increased fire hazard||During drought conditions, fuels for wildfire, such as grasses and trees, can dry out and become more flammable. Droughts can be exacerbated by exceptionally warm weather. Extreme heat, when combined with
extremely low precipitation and high temperature, can result in reduced streamflow, dry soils and large-scale tree loss. Extreme wildfires are more likely to spread quickly, burn with greater severity and be costly to put out under these conditions.
|Crop withering and dying||Drought has a perhaps unique impact on agricultural systems because of its duration, which often extends over several seasons.|
|Loss of arable land||Drought, inappropriate land use (such as monocultures) and unsustainable land management methods, such as deforestation,
improper farming practices and overexploitation of water resources) can all contribute to land degradation and loss of arable land, which is exacerbated by drought.
|Extreme weather events, such as droughts, lead to contamination of soil; agricultural lands; water, food and animal feed with pathogens;
chemicals and other hazardous. Infectious disease outbreaks may be a direct consequence of drought. When rainfall decreases, viruses,
protozoa and bacteria can pollute both groundwater and surface water.
People who draw their drinking water from private wells may be more susceptible to infectious diseases caused by the drought.
|Increased prices for farming commodities||Drought-related impacts exist in a variety of forms. Farmers who lose money because drought destroys their crops, or ranchers who may have to spend more money feeding and watering their livestock, are examples
of economic effects. Direct economic effects, such as declines in dairy production, and indirect effects, such as rises in cheese prices, are also possible.
|The increased expense of buying food and loss of income||Drought in South Africa’s Western Cape province, for example, has resulted in employment losses in the province’s agriculture sector.
According to the third quarterly labor force survey from 2017, the agricultural industry lost almost 25,000 jobs across the country. In the
Western Cape province, about 20,000 of these were lost, which has a direct impact on income generation. Many of these impacts were linked to drought events.
|Sale of livestock at reduced market price||Decreases in feed availability due to drought can lead to stunted growth, decrease milk production in dairy cattle and lower quality in beef, which
can influence a low-income generation. The weakening product-to-feed ratio, driven by the higher feed prices, will reduce profit margins
|Increased transport costs||Drought reduces cargo-carrying capacity and reduces accessible water-based transportation routes. Higher temperatures, which
frequently accompany drought, can influence pavement performance, impacting roadways and airport runways, as well as collapsing rail lines.
|Deepening poverty and increased unemployment||The drought vulnerability in South Africa, especially in the affected
provinces, is driven by extensive soil erosion, which is a result of the communal land-use system and limited access to information and infrastructure as well as low-income levels and high unemployment.
|Increased capital shortfall||With the recent drought hazards in some regions of South Africa, the economic and livelihood have been severely affected due to these
hazards. All of these have huge economic consequences. South Africa’s economy grew at an annual pace of 1.1 percent on average from 2015 to
2017, with the agricultural sector increasing at less than 0.5 percent. That is insufficient to address the country’s most pressing issues, which include high rates of inequality, poverty and unemployment.
|Increased debt and increased credit risk for financial institutions||Farmers are more vulnerable to drought because almost all their livelihood income depends on farming, the unemployment rate is very
high and opportunities for alternative jobs are scarce. More so, some farmers that are on loan or borrowed money from banks or other financial institutions are indebted with credit risk.
Disastrous consequences; Drought in Different Parts of world
Deteriorating conditions of vegetation, increased distances to water sources, worsening livestock conditions, reduced milk production and increased number of children at risk of malnutrition are common lived experiences on a day-to-day basis as a result of these increasing drought event s(Orimoloye, Belle et al. 2022).
South Africa is naturally water deficient, which adds to the climate fluctuation with the average annual rainfall in South Africa being far below the global average of 860 mm per year. Drought in South Africa’s Western Cape Province, for example, has resulted in employment losses in the province’s agriculture sector. According to the third quarterly labor force survey from 2017, the agricultural industry lost almost 25,000 jobs across the country. In the Western Cape province, about 20,000 of these were lost which has a direct impact on income generation. Many of these impacts were linked to drought events (Orimoloye, Belle et al. 2022).
In Madagascar, the situation is very grim; about 1.31 million are affected with about 60% loss and damages recorded in the agricultural section. In Angola, the situation is no different. About 3.81 million people are experiencing food insecurity as a result of drought events afflicting the country. In Kenya, the situation is almost the same, as reports from the country are stating unequivocally that food insecurity within the country is likely to persist till the end of the year 2021 with about 2 million people in need of humanitarian aid(Orimoloye, Belle et al. 2022).
In Canada, economic losses, particularly in the agricultural sector, may reach several hundred millions of dollars in a drought year, with major socio-economic repercussions affecting the entire region. Environmental damages include soil degradation and erosion, vegetation damage, slough and lake deterioration and wildlife loss(Maybank, Bonsai et al. 1995).
A severe drought struck Southeast Asia in 2004, resulting in reduced water supplies for drinking and irrigation, as well as crop loss of millions of hectares(Orimoloye, Belle et al. 2022).
Extreme Drought leads to desertification. Drought has an impact on both ecological and economic systems. Drought, similarly to land deterioration, affects almost every section of the globe, even humid areas(Orimoloye, Belle et al. 2022). Desertification is the degradation of arid, semi-arid and dry sub-humid environments when productivity is limited by water availability.
Aghelpour, P., et al. (2020). “A theoretical approach for forecasting different types of drought simultaneously, using entropy theory and machine-learning methods.” 9(12): 701.
Bazrafshan, J., et al. (2014). “Drought Monitoring Using the Multivariate Standardized Precipitation Index (MSPI).” Water Resources Management 28(4): 1045-1060.
Haile, T. J. E. J. o. A. S. (1988). “Causes and Characteristics of Drought in Ethiopia.”
Maybank, J., et al. (1995). “Drought as a natural disaster.” 33(2): 195-222.
McKee, T. B., et al. (1993). The relationship of drought frequency and duration to time scales. Proceedings of the 8th Conference on Applied Climatology, Boston, MA, USA.
Orimoloye, I. R., et al. (2022). “Drought: A common environmental disaster.” 13(1): 111.
Rahimi, J., et al. (2013). “Spatial changes of Extended De Martonne climatic zones affected by climate change in Iran.” Theoretical and Applied Climatology 112(3): 409-418.