Global Desertification Tension Zones

Hari Eswaran¹, Paul Reich¹, and Fred Beinroth²

¹USDA Natural Resources Conservation Service, Washington DC, and
²University of Puerto Rico, Mayaguez, PR

Summary

As the world’s population continues to grow, human induced stresses on biophysical resources increase proportionately. In the richer countries, environmental awareness, and the necessity to incorporate ecological considerations in land management and the ability to subscribe to tenets of sustainable agriculture have contributed to national strategies for a rational use of biophysical resources. The poorer third world countries, on the other hand, are unable to embrace these ‘lofty’ ideals and continue on the road to reduced productivity and an inability to feed themselves. It is evident that in the foreseeable future, unless the latter countries are assisted to better manage their resources and address food security through an important emphasis on soil and water conservation, the capacity of the planet as a whole to maintain an acceptable quality of life will be reduced.

Using spatial databases on global soils and climates and published information on land resource constraints, derivative maps of major land resource stresses, land quality, vulnerability to desertification, and susceptibility to wind and water erosion were developed. The soil map was also used to identify locations and extent of major constraining soils. For Africa and Asia, the analysis was further coupled to studies on population density using an interpolated population database.

There are about 7.1 million km² of land under low risk of human-induced desertification, 8.6 million km² at moderate risk, 15.6 million km²at high risk, and 11.9 million km²under very high risk. Each of these classes represents a desertification tension zone. The major critical tension zone that requires immediate attention is the very high-risk class. There are 11.9 million km² of land with about 1.4 billion inhabitants. Major national conflicts are related to the reduced ability of the land to support the people in agriculture-based economies. The need for mitigating technologies and aspects of policy intervention are elaborated.

In Press: Proc. Of International Soil Conservation Organization Conference, Purdue University, IN. 1998. (To be published as a CD).

Introduction

Feeding the burgeoning population while preserving or enhancing the quality of the environment is becoming a daunting task, particularly in third world countries (Eswaran et al., 1995). To ensure political stability in developing countries, decision-makers recognize food security as a primary concern -- one that overrides all others. The negative effects of desertification, the looming consequences of global climate change, declining productivity, uncontrolled urbanization, and the longer-term impacts of deforestation or resource exploitation become insignificant when compared with the immediate concerns of feeding the population (Durning, 1989). On the other hand, in developed countries, while the abilities to sustain food production and pay attention to environmental integrity are significantly better, food security is still not being addressed as a serious issue (Brown, 1993).

A first step in enhancing or even sustaining productivity is minimizing biotic and abiotic stresses and providing optimal environment for maximizing yields. Significant advances have been made in reducing pest and disease stresses and exploiting the genetic potential of several crops. Similar progress has been made with respect to tolerance to abiotic stresses, such as resistance to moisture stress and soil acidity. This has resulted in large areas of monoclonal cultivars, which present another threat of reduced genetic diversity. An eight to ten fold increase in crop productivity in the better-endowed regions of the world during the last few decades has resulted in grain surpluses. The focus on productivity and short-term returns to labor and capital of past decades has reduced land quality. In the soils of the tropics, which generally are of lower quality compared to temperate soils, damage to land quality and environment as a whole have reached proportions never anticipated a few decades ago (Eswaran et al., 1999).

The purpose of this study is to define and locate desertification tension zones around the world where the potential decline in land quality is so severe as to trigger a whole range of negative socioeconomic conditions that could threaten political stability, sustainability, and the general quality of life. The formal definition of desertification adopted by the United Nations Convention on Desertification is, "land degradation in arid, semi-arid, and dry sub-humid areas resulting from various factors, including climatic variations and human activities." Excluded in the definition are areas which have a "hyper-arid or a humid" climate. Under low-input agricultural systems, tension zones occur in areas where the productive capacity of the land is stressed by mismanagement, generally by resource poor farmers. The situation arises when the population supporting capacity is exceeded. In high-input systems, tension zones arise due to excessive use of agri-chemicals, uncontrolled use of irrigation, and monoclonal plantations with minimal genetic diversity. In either case, probability of failure of the system is high; the difference between the two systems is a matter of time.

Tension zones result from:

1. Excessive and continuous soil erosion resulting from over and improper use of lands especially marginal and sloping lands;

2. Nutrient depletion and/or soil acidification due to inadequate replenishment of nutrients or soil pollution from excessive use of organic and inorganic agri-chemicals;

3. Reduced water holding capacity of soils due to reduced volume of soil and reduced organic matter content, both a consequence of erosion and reduced infiltration due to crusting and compaction;

4. Salinization and water-logging from over-irrigation without adequate drainage; and

5. Unavailability of water stemming from decreased supply of aquifers and drainage bodies.

Methodology

Two databases provided the biophysical basis for our assessment: First, the FAO/UNESCO Soil Map of the World at a scale of 1:5,000,000, which is now digitally available (FAO, 1991), whose units were converted to taxa of Soil Taxonomy. Second, a climate database with records for about 25,000 stations globally, which was used in computing the soil moisture and temperature regimes. The resulting pedoclimate map was then superimposed on the soil map using Geographic Information Science (GIS). The soil and pedoclimate information was used to place each map unit into one of nine land quality classes with class one having the most favorable and class nine the least desirable attributes for grain production (Eswaran et al., 1999). To facilitate placement into these classes, a list of 24 land stresses that constrain grain production was developed. An assessment of vulnerability to desertification was then made using the procedure of Eswaran and Reich (1998).

To evaluate the number of people affected, the map of vulnerability to desertification was superimposed on an interpolated population density map developed by Tobler et al. (1995). In a second analysis, classes of population density were superimposed on the desertification map. Table 1 shows a matrix used for the analyses. Accelerated desertification takes place with increasing population density and particularly under low-input systems. In some situations, this generalization may not be true, but this assumption was made to evaluate risk of human-induced desertification. Three classes of population density -- <10, 11-40, and >41 persons/km²-- were used and a map of these three classes was superimposed on the vulnerability to desertification map. The matrix (Table 1) was developed to relate vulnerability and population density to risk of human-induced desertification.

By this approach, the tension zones are defined as in Table 1 and any land area represented by cells 7, 8, or 9, is considered as a critical desertification tension zone. Land belonging to the critical zone is moderate to highly vulnerable to desertification and in addition has a high to very high population density.

In a third step of the analysis we looked at the relation of serious conflicts in countries to risk of desertification. A conflict as defined by the International Peace Research Institute (IPRI) is one where at least 1,000 deaths resulted from a war. IPRI (1999) has documented countries with conflicts from 1989 to 1998.

Desertification

Desertification results from mismanagement of land and thus deals with two interlocking, complex systems: the natural ecosystem and the human social system. Interactions between the two systems determine the success or failure of resource management programs. With the declaration of the Convention to Combat Desertification (CCD), culminating from decisions of the United Nations Conference on Environment and Development (UNCED, 1993) there is now an international body to address the issues of desertification. The CCD is in the process of developing an agenda and action plan for this purpose. From the land resource point of view, the thrust of a new agenda for resource assessment, monitoring, and managing the land must have at least four components, which are elaborated below:

1. Assessment and monitoring

   Few will question the usefulness of soil resource information. It has been the basis for many advances in agriculture. The surpluses of agricultural products in many of the western countries and some of the developing countries are the result of judicious use of the resource base. Today, the need to preserve fragile lands and enhance or maintain production on the better-endowed soils is forcing judgments on soil quality. The role of soils as a filter of chemicals and their niche in the ecosystem also require scientists to make assessments of ecosystem health. Mitigation technology for containing greenhouse gases requires scientists to evaluate soils from another perspective. All of these rely on detailed or farm-level soil information and more precise and geo-referenced information. Environmental accounting, at the other extreme, now considers soil as a capital investment and is forcing land users to include environmental costs in their production assessment.

   The increasing demand for real-time information will require resource assessment to adapt. Monitoring of the quality of land resources will also be subject to the same demands. With a few exceptions, monitoring of soil properties and processes is not yet a science. It is envisaged that the future will require greater attention to changes of soil properties in addition to kinds of soils. Bouma and van Lanen (1987) have used pedo-transfer functions to estimate hydrologic events over a relatively short time frame and such studies lay the basis for the challenges of the next century. A few countries have initiated national resource inventories to monitor the status of the nation's resources. Periodic (every five years or more) assessments provide the basic information for national planning, developing mitigating technologies if large-scale detrimental changes are taking place, and for developing research priorities. Suitable indicators of resource quality assist in developing cost-effective assessments; however, more studies are required to develop such indicators for soil degradation.

2. Land quality and early warning indicators of desertification

   The FAO/UNESCO/UNEP 'Global Assessment of Soil Degradation' provides data, albeit subjective, to evaluate the current magnitude of the soil degradation problem (Oldeman et al., 1992). The United Nations Environment Program (UNEP) and the World Resources Institute (WRI) provide other analyses on these and other aspects of environmental degradation. Although the underlying causes of land/water degradation are socioeconomic, adjustments of these factors will not automatically restore productivity of the biophysical resource base. Thus soil and water technologies are of critical importance to ensure that production of food, fuel, and fiber can be sustained and the environment protected. Efforts to restore productivity to degraded lands should be coupled with techniques to recognize productive capacity of all soil resources. The ability to flag all stresses before productivity is significantly impaired (Brinkman, 1990) is an immediate challenge. The causes of stressed systems (Virmani et al., 1994) are numerous and include removal of nutrients, development of acidity, salinization, alkalization, destruction of soil structure, accelerated wind and water erosion and loss of organic matter. In some regions of the world, the combination of some or all of these results in such degradation that the term desertification is popularly used to describe these regions (UNEP, 1992). Finally, it must be appreciated that there are important interactions among the causes of degradation. Erosion, for example, may be flagged as the major problem where chemical degradation of the soil prevents establishment of vegetation and thus leads to an inability of the soil to stabilize against erosion. In this example, lack of appropriate vegetation becomes an early warning indicator. Very few studies have been conducted on this linkage between factors and there is an urgent need to re-evaluate this (Lal, 1994).

   Land quality is directly linked to quality of life; specifically, social and economic equity, and thus should be addressed in the socioeconomic context for sustainability. In the past, the focus of attention was on rehabilitation of degraded lands. Thrusts in the new Agenda are to evaluate the potential for land resource degradation, manage the resilience characteristics of the systems, and select technological options in the framework of the resilience properties (Eswaran, 1993). Consequently, the concepts of 'early warning indicators' and 'land resilience' are relevant (Greenland and Szabolcs, 1994). There are few methods to predict the onset of degradation, which is crucial to managing systems being stressed. The resilience capacity of systems is also less well established and this should be studied to implement remedial measures to rehabilitate degraded lands. Although soil resource information have been utilized for such purposes in developing countries, either the poor quality of information or its absence has prevented a more effective use for such purposes (Eswaran, 1992).

3. Land productivity and land use options

   Sustainable land management (SLM) is the key to harmonizing the environmental and ecological concerns of a society faced with the economic realities of producing adequate food and fiber and ensuring a basic minimal quality of life (Dumanski, et al., 1992, Smyth and Dumanski, 1993). SLM is not merely maintaining the integrity of the biophysical land resource base as sustainability can only be realized if land users understand the impacts of land management options so that they can optimize the socioeconomic and environmental benefits of their choice to attain it. Insufficient attention is given to this aspect of SLM and consequently, in addition to developing concepts, frameworks, and mechanisms of SLM, a concerted effort to link SLM to the socioeconomic realities of the farmer would be very beneficial.

   All work on global resource assessments, specifically with respect to global environmental monitoring, is hampered by a lack of data. At the other end of the spectrum, farm level data needed to transfer technology are also absent in most developing countries. Due to this information gap, simulation models and decision support systems cannot be effectively used by most developing countries.

4. Decision support systems

   Technology transfer demands changes, not only in the way materials and people are used in production, but also in the way information is managed. Decision makers in environmentally-sensitive countries with limited natural resources are expected to make technical decisions that are ecologically, economically, and socially acceptable (IBSNAT, 1993). Agenda 21 of the Rio Conference in 1992 emphasized this. The information sources for making such decisions should be easily available, organized, timely, accurate, and dependable. One approach for structuring and judging the value of information for decision making is a decision support system (DSS) such as the Decision Support System for Agrotechnology Transfer (IBSNAT, 1993).

   We should be developing a 'scale-sensitive information system' because throughout society there is a vertical network of decision makers who have access to information which permits them to make policies concerning the use and distribution of resources. Effectively addressing desertification recognizes that decision makers at all levels of society should be able to participate in the design and implementation of any tool that affects their social, economic, and ecological well-being.

   A first step in the implementation of such an agenda is the identification and location of the problem. Such a process is scale dependent and also a function of the perceived severity of the problem. In data-rich countries, productivity declines of major crops signal the need for remedial actions. However, the ability to anticipate problems is perhaps an equal or greater need. The ability to identify ‘tension zones’, which are locations of potential threats to sustainability and environmental integrity is challenging. Acceptable methodology does not exist for such an assessment.

Results and Discussion

Land quality classes (LQC) VII, VIII, and IX (Table 2) occur in the fragile ecosystems and are excluded in the following discussions due to inherent difficulties of implementing sustainable agriculture programs and also because they are excluded by the narrow definition of ‘desertification’. Figure 1 shows the global distribution of the LQCs. LQCs I, II, III, have the highest potentials and least constraints for sustainable agriculture. They occupy 13.3% of the ice-free land surface and about 1.4 billion people (24.2%) live on these lands. Class IV, V, and VI lands occupy 33.4% of the land surface and as shown in Figure 1, are present mostly in the inter-tropical areas. Most of the developing countries have large areas of such lands. About 3 billion people (52% of global population) live on these lands. They are mostly poor and practice low-input low-output agriculture. Large areas of these lands have long periods of soil moisture stress, which is the main cause of reduced soil quality. In the areas with a humid climate, plantation agriculture provides the wealth of the country.

The implication of this analysis is that more than 75% of the world’s population live in regions that do not have a high capacity for grain and feed production. When population densities were low, the land supported the people. However, with increasing population not only does the ability of the land to support the population become threatened but the negative consequences of low-input systems also systematically reduces this ability.

The land qualities and climatic properties without considering availability of irrigation were employed to make the assessment of vulnerability to desertification. Figure 2 and Table 3 show the results of this analysis. Comparing Figures 1 and 2, it is clear that many of the lands that are vulnerable belong to LQC IV, V, and VI. The high to very high desertification vulnerability classes occupy about 11.6% of the global land surface.

Desertification processes impact about 2.6 billion people or 44% of the world’s population (Table 3). Many of them are probably contributing to the process as they live in the developing countries of the world where good land management is not the rule. There are, of course, considerable differences between countries with respect to impacts of high populations to land degradation. Cleaver and Schreiber (1994) estimate that about 50% of Sub-Saharan agricultural land has lost its productivity due to degradation and about 80% of rangeland show signs of degradation. Shifting cultivation with long fallow periods and transhuman pastoralism was appropriate in the past when populations were low. However, in many countries this steady state is being tilted towards exploitation of the resource base. The slow evolution to more intensive and permanent systems without appropriate inputs is contributing to the decline of land quality. A similar process is also operating in many countries of Asia.

As shown in Table 1, a high population density in an area that is highly vulnerable to desertification poses a very high risk for further land degradation. Conversely, a low population density in an area where the vulnerability is also low poses in principle a low risk. Figure 3 shows the distribution of the risk of human-induced desertification and Table 4 gives the areas of the classes. The Mediterranean countries of North Africa are very highly prone to desertification. In Morocco, for example, erosion is so extensive that the petrocalcic horizon of some Palexeralfs is exposed at the surface. In the Sahel, there are pockets of very high-risk areas. The West African countries, with their dense populations, have major problems containing the processes of desertification. There are large areas of Central and Southern Asia, which are highly vulnerable. And in South America, the northeast corner of Brazil (the province of Pernambuco) is highly vulnerable.

There are about 7.1 million km² of land at low risk of human-induced desertification, 8.6 million km² at moderate risk, 15.6 million km²at high risk, and 11.9 million km²at very high risk. Each of these classes represents a tension zone. However, the critical tension zone, which requires immediate attention belongs to the very high-risk class. There are 11.9 million km² of such lands (Figure 3, Table 4) and about 1.413 billion people are involved. The concept of desertification suggests some or all of the following negative effects and the probability of their occurrence is highest in the tension zones:

• Systematic reduction in crop performance even leading to failure in rainfed and irrigated systems;

• Reduction in land cover and biomass production in rangeland with an accompanying reduction in quality of feed for livestock;

• Reduction of available woody plants for fuel and increased distances to harvest them;

• Significant reduction in water from overland flows or aquifers and a concomitant reduction in water quality;

• Encroachment of sand and crop damage by sand-blasting and wind erosion;

• Increased gully and sheet erosion by torrential rain;

As a consequence of some or all of these processes, there commonly occurs societal disruption due to reduction in life-support systems. It is difficult to establish cause and effect relationships between conflicts and ability of land to feed and clothe the people. In Figure 4, the location of major conflicts during the period 1988 to 1998 is indicated on the map of tension zones. The coincidence may be accidental but it does provide a reason for concern. Some high-risk countries such as Nigeria and India have not had major conflicts due to counteracting policies. However, the potential of conflict is high and continuous vigilance is necessary. The countries ravaged by civil war such as, Rwanda, Burundi, Ethiopia, Somalia, Kampuchea, and in parts of countries such as in Sri Lanka, Angola, Mexico, and former Yugoslavia may have different reasons for the conflicts. Invariably communities threatened by land shortages generally trigger it. Race, religion, origin of population and even caste may be used as reasons for the conflict but an underlying reason is generally land and its quality.

Conclusion

Designation of tension zones is an important prerequisite for formulating national policies that address land degradation and desertification. In the present global assessment, only the quality of the land and the population density are used to identify and delineate the tension zones. Knowledge of other factors, specifically socioeconomics and more detailed resource characteristics including quality and quantity of water, is necessary for national appraisal. A comprehensive analysis should consider the nexus of high population densities, quality and quantity of the resource base, agricultural production systems, and environmental factors. The next step should be to develop a framework for desertification tension zone assessment and monitoring with suitable indicators. Such an analysis would provide a basis for appropriate policies and mitigation technologies.

Identification and location of desertification tension zones in countries, if followed-up with appropriate policy decisions and action plans, will help to:

1. Enable the judicious use of land resources through protection and preservation of fragile systems and sustainable production on the better endowed areas, and targeting of research and development; ensure a balanced land use through appropriate land allocation for forestry, wild-life, agriculture, and urban use; and promote a more rational use of the scarce water resources;

2. Buffer the socioeconomic stresses and reduce economic instability and political unrest in the country as a whole; reduce pressures on affected areas and promote sustainable development outside the affected areas;

3. Alleviate pressures on biodiversity and promote environmental integrity;

4. Help reduce the iterative processes leading to global climate change through increased land cover and as a result, enhance carbon sequestration; and

5. Assure food security and a better quality of life for most of the people.

A sine qua non to help address global land resource constraints to sustainable agriculture is the identification and quantification of land resource stresses. This would assist in prioritizing the allocation of funds to alleviate constraints of poorer countries and set them on the path to sustainability. With the current knowledge of soil resources and climatic endowments of countries, it is possible to identify the tension zones and develop a basis for future quantitative assessments of land degradation and even desertification.

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