**3. Factors affecting desertification**

The process of land degradation in arid areas is called desertification, which affects the land capacity to provide ecosystem services, such as food production or biodiversity

#### *Desertification in Agricultural Lands: Approaches to Mitigation DOI: http://dx.doi.org/10.5772/intechopen.98795*

hosting, to name a few. It is stimulated by both human activity and climate and depends on the specific context. More than 1 billion people in about 100 countries face some of the risks associated with the effects of desertification [20]. The risk of desertification can increase in parts of the world that may become arid due to climate change.

According to the United Nations (UN), about 2.1 billion people worldwide (25–30%) living in arid and semi-arid regions [21] are among the poorest people. Approximately 70% of rainfed areas are located in Africa and Asia (**Figure 3**) [3]. Asia, followed by Africa and South America, have the largest populations in arid regions [23]. The global population growth rates are very high, especially in dry areas. The rapid population growth increases the pressure on land and natural resources that have already been oppressed and leads to poverty by degrading land and increasing desertification [24].

Parivar et al. [25] comparisons of open, green, and impervious surface areas (ha) in Yazd, Iran for 1991 and 2018 (**Figure 4**). The continuum, impermeable levels (built area) increased strongly during the period under study. From 1991 to 2018, there was an 80% decrease in open space, 63% decrease in green space, and a 90% increase in built-up area. In this way, population growth and urban development reduce green space, which leads to desertification.

Numerous factors affect the intensification and advancement of desertification, which can be classified into two categories, anthropogenic and climatic factors.

#### **3.1 Anthropogenic factors**

Human factors play an intensifying role in the development of desertification in arid and semi-arid ecosystems. These factors have a significant contribution to the process of land degradation. The annual plants are destroyed and the soil dries out when rainfall is low, thereby providing water and wind erosion and forming deserts and desertification globally. Some researchers have identified humans as a significant cause of desertification [4]. The shares of human factors and natural elements involved in desertification were 87 and 13%, respectively [26]. Changes in the use and destruction of forests and pastures, overgrazing, salinization of water and soil resources, burning of crop residues, improper use of groundwater, irregular

#### **Figure 3.**

*Dryland categories across geographical areas (continents and Pacific region). Data: TerraClimate precipitation and potential evapotranspiration (1980–2015) [22].*

#### **Figure 4.**

*Land areas (ha) in Yazd categorized as open, green, and built-up space (1991–2018) [25].*

plowing, and failure to observe proper crop rotation in agriculture, fire, sediment settlement, development of urban areas, and industrial activities are among the most important factors influencing desertification by humans. Deserts are divided into two general categories—natural deserts of environmental origin and human deserts. Natural deserts are commonly found in arid and hyper-arid regions of the world, and humans have a minor role in their formation, making bare natural landscapes without vegetation. In addition to arid and hyper-arid regions, human deserts can be seen in other climatic zones, including semi-arid to humid regions.

#### **3.2 Climatic factors**

Climate change can further increase the risk of desertification for those regions of the world that may change into drylands for climatic reasons. Because arid areas are used for various purposes, such as agriculture, grazing, and gathering wood for fuel, the multiple activities performed in them can exacerbate the problem of desertification and bring about lasting changes in rainfed ecosystems. In this regard, drought, irregularity in rainfall, topographic factors, and radiation angle are the most critical environmental factors affecting desertification.

Although the effects of climate change can be seen in all activities, its impact on agricultural production seems to be more pronounced; annual damage from the adverse impacts of climate change due to rising temperatures, long periods of drought and desertification has been reported to be far greater than other activities affected by this change. For example, climate change has directly reduced crop productivity by reducing crop yields [27]. Barren ecosystems have low and variable rainfall, so climate change and other factors that lead to prolonged drought can rapidly reduce these ecosystems biological productivity. These changes may be temporary and last only one season, or they may last for years and decades [3].

#### **4. The role of agriculture in desertification**

One of the most important causes of desertification, especially in arid and semi-arid regions of the world, is improper activities in agriculture. Dense and

#### *Desertification in Agricultural Lands: Approaches to Mitigation DOI: http://dx.doi.org/10.5772/intechopen.98795*

improper cultivation of crops reduce soil structure stability and lead to soil degradation and erosion [28]. When the soil's pressure increases due to agricultural operations and land clearing, soil fertility decreases, resulting in soil degradation and erosion.

Irrigation systems have developed over time as an agricultural technique in arid areas with low rainfall. If irrigation methods are misapplied, water loss and lowering of groundwater aquifers will lead to salinization and alkalinization of lands. Therefore, one of the most critical factors in desertification in agriculture is improper irrigation, which will ultimately lead to the destructive effects of drought, the phenomenon of soil and water salinization due to improper management of agricultural land [28]. Salinity is caused by improper irrigation in soils of arid and semi-arid regions. The leading cause of salinity and alkalinity in some parts of the world is the entry of low-quality water. Improper irrigation and lack of proper drainage raise the groundwater level and form a surface saline aquifer. With soil degradation, vegetation decreases and the soil is exposed to water and wind erosion, and its fertility is severely reduced. Therefore, knowing the main reasons for the salinization of soil and water in the world's regions and proper management of such lands can help reduce the process of desertification.

Changes in the soil's chemical composition with the use of fertilizers or chemical pesticides lead to changes in the soil's physical condition, which increases soil erosion. On the other hand, nitrogen released from chemical fertilizers and its mixing with groundwater lead to pollution of groundwater resources, which is recognized as a severe problem in some parts of the world [29].

Effects of fire on vegetation cover change and expedite the process of desertification by humans is proven. The severity of the fire damage depends on the conditions of the area. In arid lands, severe fires lead to the extinction of plant, animal, and soil species, which in some cases alter ecosystems and contribute to intensified desertification. Frequent burning of straw and crop residues and reducing land fertility are also influential factors in desertification.

There is an important concern about the conversion of agricultural land to barren desert, exacerbated by desertification in countries such as Iran.

#### **Figure 5.**

*Classification of Iran's land suitability for agriculture based on soil properties, terrain, and climate conditions [30].*

Accordingly, desertification is one of the most important factors in Iran, which has been exacerbated by drought. The result of drought and desertification is a reduction in Iran's land suitable for agriculture. Mesgaran et al. [30] classified Iran's land suitability for cropping as (million ha): very good 0.4% (0.6), good 2.2% (3.6), medium 7.9% (12.8), poor 11.4% (18.5), very poor 6.3% (10.2), unsuitable 60.0% (97.4), and excluded areas 11.9% (19.3) (**Figure 5**). Hence, reducing suitable land for agriculture means reducing food production, which threatens food security.
