A. Discussion paper on the preparation of the World Map of Desertization with particular reference to salinity/alkalinity problems
B. Draft Report of an FAO Expert Consultation on the Preparation of a World Map of Desertization
by
P.J. Mahler
Senior Officer, Environment Programme Coordinating Unit,
AGDE, FAO
1. BACKGROUND
Resolution 3337 (XXIX) of the UN General Assembly requests the preparation of a world map of the areas affected or likely to be affected by desertization.
The objective of this map is to serve as a background document for an intergovernmental Conference on Desertization planned to be held in 1977.
The map should be published by the end of 1976. Taking into account the time required for proof-checking and printing (6 months), the master copy of the map should be ready by July 1976. Considering other delays for recruiting personnel and for establishing arrangements with contributing institutions, the time left for the actual preparation of the map is less than one year.
2. GENERAL CONSIDERATIONS
2.1 Definitions
There is no agreed definition of desertization. The word “desertification” is something used instead of desertization. Some consider “desertification” to be man-made desertization - desertization encompassing both natural and man-induced causes of extension of deserts. In the context of the project it is proposed to use the following definitions: “the development outside desert areas and within arid and semi-arid areas, of landscape features of the deserts”.
This definition calls for discussion on several points:
i. it restricts desertization to arid and semi-arid areas;2.2 The Scaleii. it does not specify either the causes or the processes of desertization;
iii. “Landscape features of the deserts” have to be defined. These may include sand dunes, rock debris, salt flats, badlands, hamadas, denuded mountains and barren plains;
iv. “the development of the landscape features” includes the consideration of all possible intergrades between the above desert features and those of the arid and semi-arid areas as well as the occurrence of these landscape features by patches.
The time constraints set for the preparation of the map and its aims (e.g. consideration by a political gathering) imply the preparation of a simple generalized map of a rather complex set of features on which limited cartographic information is available.
Guidance is invited on the selection of the scale:
i. a scale of 1:10 million would require the publication of about six sheets which does not seem feasible in the time allotted for the preparation;2.3 The Legendii. a scale of about 1:25 million would match the scale of the Map of Meigs on arid homoclimates. However, very little information can be provided at this scale.
The legend should comply with the requirements of the UN General Assembly resolution, e.g. it should theoretically distinguish between areas already affected and those likely to be affected by desertization. It should be noted, however, that an area already affected by a certain type of desertization is quite often likely to be affected by another. Moreover the likelihood of desertization depends both on the inherent vulnerability of the landscape to degradation (slope, soil texture, aggressivity of climate) and on human influences, either positive (protection, management, reclamation) or negative (degradation).
For this, guidance is invited on the elaboration of the legend:
i. by “areas already affected by desertization” it is proposed to understand essentially those areas which have already acquired strongly developed desert features, e.g. sand dunes, badlands, strongly saline areas; all the other areas would be considered as areas likely to be affected and would be assessed according to their inherent vulnerability (thus excluding human influences);5. DESERTIZATION AND SALINITY/ALKALINITYii. among the areas likely to be affected, only those which are highly and moderately vulnerable would be indicated (as one single category) on the map; the slightly vulnerable areas would not be shown on the map. The most critical areas could be shown by a map symbol (e.g. without delineation of the areas);
iii. the legend would distinguish among different processes of desertization and for each of these processes would separate into two categories, e.g. “already affected” and “highly to moderately vulnerable” would be shown. Among the processes to be distinguished one may consider:
a. salinization and/or alkalization,iv. it is very clear that at the scale considered and with the information available the assessment of the vulnerability to desertization can only be made by judgement. However, it will be essential to develop criteria and a method of assessment which include consideration of soil characteristics, climate, land form and vegetation in order to ensure consistency in the assessment.
b. development of shifting sands,
c. denudation of vegetation,
d. denudation of hard rock or hard pan,
e. development of badlands on soft material.
The development of salinity and alkalinity features in arid and semi-arid landscapes depends both on inherent factors (presence of saline rocks, depth of groundwater, occurrence of saline waters, land form and soil drainage) and on human influences (irrigation, reclamation, denudation or protection of watersheds, etc.).
Comments were invited on the aspects of salinity/alkalinity which should be included in the World Map of Desertization, such as:
i. should the areas undergoing salinization by irrigation be shown and how? - by map symbols or by special mapping units?ii. can alkalinization be distinguished from salinization at the scale contemplated for the map?
1/ The consultation was held on the occasion of the FAO/ISSS Expert Consultation on Prognosis of Salinity and Alkalinity, FAO, Rome, 3-6 June 1975.1. BACKGROUND
1.1 The expert consultation met on 4 June 1975 at FAO Headquarters, Rome, under the chairmanship of Professor V.A. Kovda; Director of the Institute of Agrochemistry and Soil Science, USSR, and President of SCOPE2/. The list of participants is attached in Annex 2.
2/ SCOPE - Scientific Committee on Problems of the Environment1.2 The consultation was held as a follow-up to a decision by the Administrative Committee on Coordination of the United Nations to entrust FAO with the responsibility of acting as focal point in the UN system for cooperation for the preparation of a World Map of Desertization.
1.3 This undertaking stemmed from Resolution 3337 (XXIX) of the UN General Assembly to hold a UN Conference on Desertization in 1977. The resolution requested inter alia the “preparation of a world map of areas affected and areas likely to be affected by the process of desertification”.
2. PURPOSE OF TEE MAP
2.1 It was noted that the map should be published by the end of 1976. Taking into account the time required for proof-checking and printing (6 months), the master copy of the map should be ready by July 1976. Considering other delays for recruiting personnel and for establishing arrangements with contributing institutions, the time left for the actual preparation of the map was less than one year. The expert consultation therefore recognized that only a generalized map could be prepared in such a short time.
2.2 Taking this time constraint into consideration, the expert consultation considered that the main purposes of such a map should be:
i. to provide on a global geographical basis and with a uniform presentation, a preliminary synthesis of the available cartographic information on desertization;3. SCOPE OF THE MAPii. to mobilize social and political awareness of the problem;
iii. to serve, with other background documentation, as a basis for stimulating international cooperation for further assessing and combatting desertization, in particular, for locating homogeneous areas and representative sites for regional cooperation of national activities for research, monitoring and conservation and development programmes;
iv. to serve as a framework for more detailed surveys in selected areas.
3.1 It was noted that there is no agreed definition of desertization and that the term “desertification” was sometimes used instead of desertization. “Desertification” was sometimes considered to be man-made desertization - desertization encompassing both natural and man-induced causes of extension of deserts. In the context of the proposed project the Expert Consultation generally agreed to use the following definition: “the development outside desert areas and within arid and semi-arid areas, of landscape features of the deserts”.
3.2 It was, however, stressed that the use of this definition would restrict the map to arid and semi-arid areas. While recognizing that desertization quite evidently occurs outside desert areas, the Expert Consultation recognized that the delineation of “true desert” areas would raise problems, especially the differentiation between man-made and natural deserts. It was generally agreed that consideration of precipitation alone would not provide a satisfactory criterion and that potential evapotranspiration and precipitation had to be considered together. It was felt that a revised version of the Unesco Map of Arid Homoclimates (Meigs) could provide a suitable basis for delineation of desert, arid and semi-arid areas for the purposes of a generalized map. The group finally agreed that the Desertization Map should include consideration of hyper-arid, arid and semi-arid areas and natural deserts outside these areas.
3.3 Other climatic factors which should be considered were, in particular:
i. the differences between cold, cool and hot deserts (as distinguished in Meig's Map of Arid Homoclimates);In this respect, it was recognized that the frequency of droughts was an important factor in assessing desertization and desertization hazards. However, many other factors had to be assessed concurrently since different degrees of desertization could develop under human influences within areas having the same drought hazard. In this connection the Chairman presented the outline of a World Map of aridity and drought probability differentiating eight categories of arid areas on the basis of frequency of drought, soil and physiographic features. This map and its legend are reproduced in this report. While recognizing that other desertization features would have to be considered, the group agreed that this integrated approach deserved careful consideration and recommended that this map, with others mentioned below in the report, should be used as an important input for the preparation of the desertization map.ii. the reliability of the rainfall or, in other words, the frequency of droughts.
3.4 The group also recommended the consideration of other factors such as:
i. the potential productivity (expressed in dry biomass) and the related data provided by the International Biological Programme;It was, however, recognized that information on these factors was often incomplete or unreliable and difficult to combine with the available information on physical factors. While these factors would have to be taken into account in the process of assessment of desertization, most of the relevant information would not appear on the map but rather in the accompanying report. To the extent possible, it was recommended, however, that the present limit of cultivated (rainfed) areas be shown on the map.ii. the present land use and present land productivity;
iii. human/“social” factors such as density of human population, availability of water from wells and streams and percentage of cultivated lands.
4. SCALE OF THE MAP
The group recognized that, for the consideration by government delegates at the Conference, a simple map on a small scale would have to be produced. It also recognized that the time constraints set for the preparation of the map would make it impossible to prepare a map at 1:5 million (some 18 sheets) or even 1:10 million (6 sheets) covering all arid and semi-arid areas of the globe. It was therefore agreed that a generalized world map of desertization would have to be prepared at a scale of about 1:25 million, possibly on the same cartographic base as that of the arid homoclimates.
The group was, however, doubtful about the scientific value of the information which could be conveyed at this scale if no other more detailed cartographic material was prepared and presented concurrently. It therefore strongly recommended that:
i. all the work of analysis and interpretation of data and information available be carried out at the scale of 1:5 million. This scale is that of the Soil Map of the World and the Map of Salt-affected Soils, and will be the scale of the World Map of Soil Degradation1/ which will proceed in close cooperation with the preparation of the desertization map;GLOBAL ARIDITY and DROUGHT PROBABILITYii. a desertization map at 1:5 million scale be prepared concurrently for a region (Africa north of Equator was suggested as a sample region) to illustrate the nature of the simplification and generalization processes which were involved in the preparation of the map at 1:25 million scale;
iii. a series of more detailed maps on sample areas should be presented at scales in the order of 1:100 000 in a few selected representative regions;
iv the mapping criteria and mapping legends of the maps at 1:25 million, 1:5 million and in the order of 1:100 000 should be consistent with each other in order to clearly show the relationships between the three levels of generalization. The preparation of these maps should therefore be carefully coordinated and prepared jointly.
1/ The preparation of the World Map of Soil Degradation at 1:5 million is expected to proceed concurrently. However, it will not be completed for the Conference.
Prepared by V.A. Kovda and S.K. Onuchenko, 1975LEGEND TO THE GLOBAL ARIDITY AND DROUGHT PROBABILITY MAP
1. Areas of sporadic very rare droughts; probability 3-5%; areas transitional to humid zones; pH of order 7-6.5; CaCO3 represented by residual concretions and irregular patches in subhumic strata.
2. Rare drought; probability of 10-15%; areas of accumulation of secondary compounds of sesquioxides and calcium carbonate; steppes, prairies, savanna, Mediterranean cinnamonic areas.
3. Frequent drought; probability 20-25%; areas of accumulation of considerable amounts of calcium carbonate, sometimes sodium bicarbonate; dry steppes, dry savanna.
4. Very frequent droughts; probability 40-50%; areas of accumulation of calcium carbonate, presence of sodium bicarbonate, sometimes considerable amounts of exchangeable sodium; semi-deserts, grey earth, chestnut soils and others.
5. Fine earth, lowlands, with accumulation of calcium carbonate, calcium sulphate with an admixture of soluble salts; extremely arid areas with droughts dominating up to 60-70% of the time (frequency).
6. Sandy and stoney surface deposits saturated with calcium carbonate, gypsum with admixture of sodium sulphate and sodium chloride; arid deserts with areas of shifting sand and salt dunes and with incidental irregular moist years, drought dominating up to 90-95% of the time (frequency).
7. Mountainous arid desert soils and parent rocks unleached with calcium carbonate, calcium sulphate, soluble salts; phenomena of erosion and deflation; absolute dominance of aridity in the order of 95% of the time.
8. The most extremely arid deserts of the globe; accumulation of soluble salts and particularly nitrates, iodates, calcium and magnesium chlorides; deep deposits of gypsum, sodium sulphate and calcium carbonate; absolute dominance of aridity with drought probability of 100% and with exceptionally rare rainy spells.
5. THE MAP LEGEND
5.1 The legend should comply with the requirements of the UN General Assembly resolution, e.g. it should theoretically distinguish between areas already affected and those likely to be affected by desertization. It should be noted, however, that an area already affected by a certain type of desertization is quite often likely to be affected by another. Moreover the likelihood of desertization depends both on the inherent vulnerability of the landscape to degradation (slope, soil texture, aggressivity of climate and other natural factors) and on human influences, either positive (protection, management, reclamation) or negative (degradation). For instance, it was considered essential that, to the extent possible, a distinction should be made between the areas where sandy deserts develop naturally as part of a geological and geomorphological process and those where sandy deserts develop as a result of human influence.
5.2 The group generally agreed to the following guidelines for the elaboration of the map legend:
i. by “areas already affected by desertization” it is proposed to understand essentially those areas which have already acquired strongly developed desert features, e.g. sand dunes, badlands, strongly saline areas, hammadas, rock debris, and barren plains; ail the other areas would be considered as areas likely to be affected and would be assessed according to their inherent vulnerability (thus excluding human influences). To the extent feasible, however, map symbols would be used to identify areas where desertization develops as a result of strong human influences;5.3 The group recognized that the experience already gained in the preparation of the World Map of Salt Affected Soil could be usefully extended to other kinds of degradation processes, in particular, the concepts used for the construction of the legend. It was also noted that the FAO/Unesco Soil Map of the World could provide most of the required basic information on the development of shifting sands, the denudation of hard rock or hard pans and the development of badlands. The legend of the Soil Map of the World also provided a useful distinction in the moisture regime of the soils of arid and semi-arid areas (Yermosols and Xerosols). It was also noted that the use of remote sensing imagery would provide useful additional information.ii. among the areas likely to be affected only those which are highly and moderately vulnerable would be indicated (as one single category) on the map; the slightly vulnerable areas would not be shown on the map. The most critical areas could be shown by a map symbol (e.g. without delineation of the areas);
iii. besides distinguishing among different kinds of present desert areas, the legend would distinguish within arid and semi-arid areas between different processes of desertization and for each of these processes separated into two categories, e.g. “already affected” and “highly to moderately vulnerable” would be shown. Among the processes to be distinguished one may consider:
a. salinization and/or alkalization,iv. at the scale considered and with the information available the assessment of the vulnerability to desertization can only be made by judgement. However, to ensure consistency in the assessment, it is essential that criteria and a method of assessment be developed on the basis of soil characteristics, climate, land form and vegetation.
b. development of shifting sands (encroachment) and wind blowing (deflation),
c. destruction of natural vegetation1/
d. denudation of hard rock or hard pans,
e. development of badlands on soft material.1/ in areas where no other degradation process occurs.
5.4 The group considered that the assessment of the process of degradation of the natural vegetation would raise problems since there was no cartographic document available for vegetation on a worldwide basis similar to that for soil resources. It was, however, recognized that the degradation of natural vegetation was an integral part of the process of desertization in certain areas. The map could not therefore be based only on the consideration of physical factors such as soil, climate and physiography.
6. CONCLUSIONS
The Expert Consultation stressed that an integrated ecological approach should be used in the preparation of the map rather than an approach which would only consider individual physical factors of desertization. It recognized that the map would only represent a first approximation which would be used to promote national activities to arrive at a better assessment of the problems.
The group also considered that desertization was a major aspect but only one among many others which lead to the environmental degradation of land resources. Recognizing the importance of the problem, it recommended that the Director-General of FAO give consideration to the establishment of an advisory panel which would regularly review the state of degradation of land resources on a worldwide basis and guide the development of international cooperation for the assessment of land degradation and/or its monitoring and control.
