1. Introduction

The land provides vital resources to support life on Earth. Land ecosystems services have social, cultural, and spiritual benefits and promote human health and well-being. However, human activities, particularly ongoing unsustainable land practices, are negatively impacting ecosystems through desertification, land degradation and drought (DLDD).

Land resources are vital for human health, well-being and, overall, life on earth. Land provides ecosystem services, as well as social, cultural, spiritual and economic benefits that form a life support system for human health and well-being^[1][2]. Vital resources provided from ecosystems include food and essential nutrients; clean water and air; shelter; medicines and medicinal compounds; wood; fuel; fiber; energy; climatic constancy; regulation of risks of natural hazards and diseases; pollination; water purification; livelihoods; and cultural, spiritual and recreational enrichment^[3][4]. Other benefits are related to biodiversity, which includes diversity within and among ecosystems and species that are essential to ecosystem functions and service delivery, as well as to the sustenance of human health and human well-being^[5][6]. Human activities are negatively affecting ecosystem services and biodiversity through land degradation^[2][4]. The drivers of land degradation and biodiversity loss are linked to population growth and rising urbanization, increased consumption, the expansion of crop and grazing lands, and unsustainable agricultural and forestry practices; these are within the context of unsustainable economic growth. In addition, climate change can affect the conditions of environmental and human systems, adversely impacting sustainable development ^[2][7][8]. The degradation of terrestrial and aquatic ecosystems is a problem of global dimensions. It affects every continent, from countries with large landmasses to small island states, from wet and dry regions to cold and warm ones, from wealthy developed countries to poorer developing countries. At least 3.2 billion people worldwide are affected by this complex phenomenon^[8]. The most vulnerable and threatened land areas are the world’s drylands, although land degradation is also a large problem outside drylands^[9]. The negative impacts are disproportionately felt by people living in vulnerable conditions. These include poor women, indigenous communities, children, elderly persons, people living in rural, marginal or fragile environments, on land that is particularly vulnerable to degradation, as well as those with a low-income or living in poor areas^{[10][11][12][13]}. This also applies to those without easy access to health care facilities and persons with pre-existing health conditions^[11][14][15]. Similarly, DLDD poses multiple risks to livelihoods, and consequently, to human health^[16][17]. DLDD reduces food production, freshwater access and ecosystem resources; as a result, health is placed under increasing stress.

Land resources are vital for human health, well-being and, overall, life on earth. Land provides ecosystem services, as well as social, cultural, spiritual and economic benefits that form a life support system for human health and well-being [1,2]. Vital resources provided from ecosystems include food and essential nutrients; clean water and air; shelter; medicines and medicinal compounds; wood; fuel; fiber; energy; climatic constancy; regulation of risks of natural hazards and diseases; pollination; water purification; livelihoods; and cultural, spiritual and recreational enrichment [3]. Other benefits are related to biodiversity, which includes diversity within and among ecosystems and species that are essential to ecosystem functions and service delivery, as well as to the sustenance of human health and human well-being [4,5]. Human activities are negatively affecting ecosystem services and biodiversity through land degradation [2,6]. The drivers of land degradation and biodiversity loss are linked to population growth and rising urbanization, increased consumption, the expansion of crop and grazing lands, and unsustainable agricultural and forestry practices; these are within the context of unsustainable economic growth. In addition, climate change can affect the conditions of environmental and human systems, adversely impacting sustainable development [2,7,8]. The degradation of terrestrial and aquatic ecosystems is a problem of global dimensions. It affects every continent, from countries with large landmasses to small island states, from wet and dry regions to cold and warm ones, from wealthy developed countries to poorer developing countries. At least 3.2 billion people worldwide are affected by this complex phenomenon [8]. The most vulnerable and threatened land areas are the world’s drylands, although land degradation is also a large problem outside drylands [9]. The negative impacts are disproportionately felt by people living in vulnerable conditions. These include poor women, indigenous communities, children, elderly persons, people living in rural, marginal or fragile environments, on land that is particularly vulnerable to degradation, as well as those with a low-income or living in poor areas [25,26,27,28]. This also applies to those without easy access to health care facilities and persons with pre-existing health conditions [26,29,30]. Similarly, DLDD poses multiple risks to livelihoods, and consequently, to human health [15,17]. DLDD reduces food production, freshwater access and ecosystem resources; as a result, health is placed under increasing stress.

2. DLDD Pathways Affecting on Human Health

Land degradation can cause water and food insecurity, unemployment, gender inequality, conflict and migration. All ecosystem consequences from DLDD can affect human health and well-being, directly or indirectly, alone or combined^[18]. Although land degradation is a major contributor to climate change^[8], climate change also can aggravate these impacts, causing substantial costs in the environmental, social, economic and political dimensions, including in the health sector^{[18][19][20][21]}. Climate change can exacerbate impacts on human health associated with DLDD (e.g., impacts from hot temperatures, from intense and prolonged extreme events such as drought and floods, and from declining freshwater resources and food security). Climate change accelerates soil erosion on degraded land through extreme weather events, which can increase the risk of forest fires. It can cause changes in the distribution of invasive species, vectors, pests and pathogens^[8][20], influencing the occurrence of newly emerging diseases, such as zoonotic infections and vector-borne diseases, in areas without previous exposures^{[22][20][21][23][24][25]}; and airborne pollutants can increase respiratory diseases^[26].

Land degradation can cause water and food insecurity, unemployment, gender inequality, conflict and migration. All ecosystem consequences from DLDD can affect human health and well-being, directly or indirectly, alone or combined [20]. Although land degradation is a major contributor to climate change [8], climate change also can aggravate these impacts, causing substantial costs in the environmental, social, economic and political dimensions, including in the health sector [20,32–34]. Climate change can exacerbate impacts on human health associated with DLDD (e.g., impacts from hot temperatures, from intense and prolonged extreme events such as drought and floods, and from declining freshwater resources and food security). Climate change accelerates soil erosion on degraded land through extreme weather events, which can increase the risk of forest fires. It can cause changes in the distribution of invasive species, vectors, pests and pathogens [8,33], influencing the occurrence of newly emerging diseases, such as zoonotic infections and vector-borne diseases, in areas without previous exposures [16,33–37]; and airborne pollutants can increase respiratory diseases [38].

There is a complex relationship between DLDD and health. The causal chain from DLDD through food, water, air and soil quality is mediated by social, economic and other environmental factors and by the response of the health system. Social and economic factors can contribute to vulnerabilities at the local level, especially in poor communities and in cases where the impacts are of long duration. The health outcomes are infectious, parasitic and nutritional diseases; non-communicable diseases; and injuries (unintentional and intentional). Most of the impacts on human health by key DLDD pathways (water security and safety, food security and safety, air quality, and soil quality) are difficult to measure because they are indirect and mediated by global and local environmental, and by social and economic forces, which all are determinants of health. Additionally, the quality of, and access to, health care services also act as mediating factors. Examples of health impacts associated with DLDD drivers are summarized in

Table 1

.

 Table 1. DLDD drivers affecting human health through water security and safety, sanitation and hygiene, food security and safety, and air and soil quality.

Source: Complete references can be found in Sena & Ebi (2021).

3.  Challenges and Directions to Improve Human Livelihoods

Complex and intermingled environmental and social challenges of DLDD affect communities and population health. Four of the many challenges were highlighted in the UNCCD Strategic Framework 2018–2030: poverty and forced migration (key social challenges); and lack of water security and lack of food security (key environmental challenges).

Poverty

Lower-income groups are more dependent on the agricultural sector, as compared to the general population, and have access to land with lower productivity, intensifying poverty and income inequality^[6][20][45]. The outcome of the analysis in selected low- and middle-income countries showed that people living on fragile lands presented a higher overall proportion of rural poverty^[14]. By 2050, four billion people are projected to live in dryland areas with decreased land productivity. This, coupled with poverty and other social stresses, can make people more vulnerable to socioeconomic instability and violent conflict^[45]. Poverty and lack of access to health care form a complex vicious cycle. Poverty leads to ill health that can maintain poverty^[46][47]. Although access to health care services is improving in low- and middle-income countries, there are large differences in the equity of access. Poverty and gender inequality are associated with lower levels of power and access to choices and resources^[48]. For example, poor people have less or limited access to services in some settings, which in turn may result in an increased burden of disease^[14][46].

Lower-income groups are more dependent on the agricultural sector, as compared to the general population, and have access to land with lower productivity, intensifying poverty and income inequality [6,33,138]. The outcome of the analysis in selected low- and middle-income countries showed that people living on fragile lands presented a higher overall proportion of rural poverty [27]. By 2050, four billion people are projected to live in dryland areas with decreased land productivity. This, coupled with poverty and other social stresses, can make people more vulnerable to socioeconomic instability and violent conflict [138]. Poverty and lack of access to health care form a complex vicious cycle. Poverty leads to ill health that can maintain poverty [127,131]. Although access to health care services is improving in low- and middle-income countries, there are large differences in the equity of access. Poverty and gender inequality are associated with lower levels of power and access to choices and resources [135]. For example, poor people have less or limited access to services in some settings, which in turn may result in an increased burden of disease [29,127].

Forced Migration

DLDD has a complex and frequent association with population migration. Annually, tens of millions of people, many living in rural areas of low- and middle-income countries, migrate for reasons related to land degradation (e.g., food scarcity), extreme weather and climate events (e.g., drought, floods), and the effects of climate change on food security^[49]. Depletion of natural resources due to environmental degradation also poses risks for rural

DLDD has a complex and frequent association with population migration. Annually, tens of millions of people, many living in rural areas of low- and middle-income countries, migrate for reasons related to land degradation (e.g., food scarcity), extreme weather and climate events (e.g., drought, floods), and the effects of climate change on food security [78]. Depletion of natural resources due to environmental degradation also poses risks for rural

people’s subsistence, especially those depending on agricultural production, livestock, fisheries and forest-based livelihoods. Intervening mediating factors include social, economic, political infrastructure, and demographic factors ^[50][45]. International migration occurs mainly from low- and middle-income to high-income countries. The most common internal migration pattern occurs from rural to urban areas, and also within rural areas and between cities (inter-urban migration). The temporal dimensions vary, which can be temporary or permanent^[50]. People who migrate can face many challenges at different stages of migration. They may experience violence and discrimination in the places where they transit through or migrate to^[51]. There are challenges faced by families left behind, especially if they do not have the ability to cope with economic, social, environmental, political and security vulnerabilities^{[14][30][52][53]}. Socioeconomic inequality is a key factor in driving the migration process in areas with land degradation; the degree of vulnerability is amplified when coupled with social injustice and unsustainable development^[49][54]. Migration and family disruption can also increase health problems, including mental health, and create other family and social changes; this also predominantly affects poor people, who do not have the necessary financial conditions to receive adequate health care ^[14][35].

people’s subsistence, especially those depending on agricultural production, livestock, fisheries and forest-based livelihoods. Intervening mediating factors include social, economic, political infrastructure, and demographic factors [53,138]. International migration occurs mainly from low- and middle-income to high-income countries. The most common internal migration pattern occurs from rural to urban areas, and also within rural areas and between cities (inter-urban migration). The temporal dimensions vary, which can be temporary or permanent [53]. People who migrate can face many challenges at different stages of migration. They may experience violence and discrimination in the places where they transit through or migrate to [140]. There are challenges faced by families left behind, especially if they do not have the ability to cope with economic, social, environmental, political and security vulnerabilities [29,46,142,143]. Socioeconomic inequality is a key factor in driving the migration process in areas with land degradation; the degree of vulnerability is amplified when coupled with social injustice and unsustainable development [78,120]. Migration and family disruption can also increase health problems, including mental health, and create other family and social changes; this also predominantly affects poor people, who do not have the necessary financial conditions to receive adequate health care [29,49,62].

Water Security

Current levels of water withdrawals are not sustainable. Water demand between 2015 and 2030 is expected to increase by 30 percent, a situation that is already leading to conflicts in some parts of the world^[55][56]. Climate change is an important additional driver of water scarcity. There is robust evidence as to its role in the reduction of renewable surface water and groundwater resources in most dry subtropical regions in the near future. Greater variability of precipitation can cause short-term shortages due to increased runoff in some water-stressed areas, reduced seasonal distribution of change in streamflow, and reduced snow and ice storage. In addition, the availability of drinking water can be impaired by the presence of algae-producing toxins caused by high temperature and by pathogens and pollutants ^{[57][58][59][60]}. This will have clear implications for agriculture and livestock, and therefore for food security, as multiple sectors compete for water resources^[59]. Population health can suffer if health services are affected by a lack of water security and water quality. This can occur due to deficiencies in health care procedures and worsening health working conditions^[14][29][61]. There is a medium- to near-term (2030–2040) risk of significantly reduced renewable water resources in most dry subtropical regions, but adaptation mechanisms can reduce the risk to the category of low-risk^[59].

Current levels of water withdrawals are not sustainable. Water demand between 2015 and 2030 is expected to increase by 30 percent, a situation that is already leading to conflicts in some parts of the world [145,146]. Climate change is an important additional driver of water scarcity. There is robust evidence as to its role in the reduction of renewable surface water and groundwater resources in most dry subtropical regions in the near future. Greater variability of precipitation can cause short-term shortages due to increased runoff in some water-stressed areas, reduced seasonal distribution of change in streamflow, and reduced snow and ice storage. In addition, the availability of drinking water can be impaired by the presence of algae-producing toxins caused by high temperature and by pathogens and pollutants [47,51,52,84]. This will have clear implications for agriculture and livestock, and therefore for food security, as multiple sectors compete for water resources [52]. Population health can suffer if health services are affected by a lack of water security and water quality. This can occur due to deficiencies in health care procedures and worsening health working conditions [29,47,60]. There is a medium- to near-term (2030–2040) risk of significantly reduced renewable water resources in most dry subtropical regions, but adaptation mechanisms can reduce the risk to the category of low-risk [52].

Food Security

One of humanity’s greatest challenges is to ensure healthy diets for a growing world population while ensuring healthy and sustainable food systems. Globally, more than 820 million people have insufficient food, leading to malnutrition and the risk of infectious diseases. An even larger number of people consume an unhealthy diet that contributes to premature death and morbidity from non-communicable diseases. These extremes occur while pressures on food systems increase^[62]. As populations increase and standards of living and nutrition improve, the demand for food will continue to rise. The current world population is 7.7 billion and is projected to increase to 8.5 billion in 2030, to 9.7 billion in 2050, and higher towards the end of the century^[63], with much of the rate of growth in low-income countries^[64]. This growth will add further pressure on land-based and aquatic food-producing systems^[65]. The challenge is how to produce more food, of better nutritional quality, for an increasing population but without further stressing the land.

One of humanity’s greatest challenges is to ensure healthy diets for a growing world population while ensuring healthy and sustainable food systems. Globally, more than 820 million people have insufficient food, leading to malnutrition and the risk of infectious diseases. An even larger number of people consume an unhealthy diet that contributes to premature death and morbidity from non-communicable diseases. These extremes occur while pressures on food systems increase [147]. As populations increase and standards of living and nutrition improve, the demand for food will continue to rise. The current world population is 7.7 billion and is projected to increase to 8.5 billion in 2030, to 9.7 billion in 2050, and higher towards the end of the century [148], with much of the rate of growth in low-income countries [149]. This growth will add further pressure on land-based and aquatic food-producing systems [150]. The challenge is how to produce more food, of better nutritional quality, for an increasing population but without further stressing the land.

4. Urgent Actions Are Required

 The current state of DLDD calls for urgent actions to protect human health and wellbeing. Lack of awareness of DLDD and its drivers and impacts are a barrier to action. Raising knowledge and awareness of the DLDD driving forces and consequences in the social, economic and environmental dimensions is crucial and should be implemented at every level. Actions across jurisdictions and sectors are needed at every stage of the pathways from DLDD drivers, their exposures, and their human health impacts^[18][66]. Responding to DLDD challenges will need a global effort. Governments, communities, civil society and the private sector play important roles in DLDD and in responding to current and emerging environmental challenges. Simultaneously, the social determinants of health need to be addressed, such as poverty reduction, water and food security, livelihood support, capacity building, and overall building resilience and human development. A better understanding of the relationship between ecosystem sustainability and health benefits would be an important contribution to decision-making regarding health and environment management (including water, land, food, air, soil). This would ensure benefits to the health and well-being of all^{[3][16][67][28]}.

The current state of DLDD calls for urgent actions to protect human health and wellbeing. Lack of awareness of DLDD and its drivers and impacts are a barrier to action. Raising knowledge and awareness of the DLDD driving forces and consequences in the social, economic and environmental dimensions is crucial and should be implemented at every level. Actions across jurisdictions and sectors are needed at every stage of the pathways from DLDD drivers, their exposures, and their human health impacts [20,162]. Responding to DLDD challenges will need a global effort. Governments, communities, civil society and the private sector play important roles in DLDD and in responding to current and emerging environmental challenges. Simultaneously, the social determinants of health need to be addressed, such as poverty reduction, water and food security, livelihood support, capacity building, and overall building resilience and human development. A better understanding of the relationship between ecosystem sustainability and health benefits would be an important contribution to decision-making regarding health and environment management (including water, land, food, air, soil). This would ensure benefits to the health and well-being of all [3,15,23,24].

References available at:

 Sena, A.; Ebi, K. When Land Is Under Pressure Health Is Under Stress. Int. J. Environ. Res. Public Health 2021, 18, 136. https://dx.doi.org/10.3390/ijerph18010136