L'hydrologie tropicale: séoscience et outil pour le développement (Actes de la conférence de Paris, mai 1995). IAHS Publ. no. 238, 1996. 113

Addressing arid zone problems

A. J. ASKEW Hydrology and Water Resources Department, WMO, CP 2300, CH-1203 Genève 2, Switzerland

J. C. RODDA International Association of Hydrological Sciences, Institute of Hydrology, Wallingford, Oxfordshire OX10 8BB, UK

Abstract During his half a century in hydrology, Jean Rodier spent a considerable amount of time and effort attending to the problems of the arid and semiarid areas of the world. Much of his work was for Orstom, but part of it was for the World Meteorological Organization (WMO) and for other international bodies. This paper outlines some of Jean Rodier's interests in this area, particularly in the WMO context. It considers his views of the hydrological aspects of drought and his work for the Operational Hydrology Programme. It reports several of WMO's subsequent activities in hydrology and water resources in relation to climate change. The paper goes on to deal with more recent events concerned with desertification and drought in the context of the follow up to the UN Conference on the Environment and Development (UNCED). It considers the role of the several bodies active in the field and leads on to discuss the Convention to Combat Desertification. It concludes with a review of WMO's recent studies, supported by Orstom and several other bodies, on water availability in dry lands for the International Panel of Experts on Desertification (IPED) of the Intergovernmental Negotiating Committee for a Convention to Combat Desertification.

L'étude des problèmes rencontrés dans les zones arides

Résumé Pendant un demi siècle d'activité en hydrologie, Jean Rodier a consacré beaucoup de temps et d'efforts à l'étude des problèmes rencontrés dans les zones arides et semi-arides du monde. L'essentiel de ses travaux a été accompli dans le cadre de l'Orstom, mais une partie le fut également avec l'Organisation Météorologique Mondiale (OMM) et d'autres organisations internationales. Cette communication présente quelques uns des points auxquels Jean Rodier s'est intéressé dans ce domaine et plus particulièrement ceux qui relèvent des activités de l'OMM. Elle considère ses vues sur les aspects hydrologiques de la sécheresse et ses travaux pour le Programme d'hydrologie opération­nelle. Elle relate plusieurs des activités développées ensuite par l'OMM en hydrologie, en relation avec l'étude du changement climatique. Enfin, cette communication aborde des événements plus récents, relatifs à la désertification et à la sécheresse, dans le contexte des suites données à la Conférence des Nations Unies sur l'environnement et le développement

114 A. J. Askew & J. C. Rodda

(CNUED). Elle considère le rôle de plusieurs organisations travaillant dans ce domaine. La discussion s'oriente sur la convention pour combattre la désertification. En conclusion, on se livre à une revue des études sur la disponibilité en eau dans les régions sèches, que l'OMM, appuyée par l'Orstom et d'autres organismes, a entrepris récemment pour le Groupe international d'experts de la désertification (IPED), du Comité intergouvernemental de négociation chargé d'élaborer une convention sur la lutte contre la désertification.

THE ARID ZONE

In his introduction of « Aspects of arid zone hydrology », Jean Rodier (1985) captured succinctly the challenges which are facing this arid third of the world's surface, covering the deserts, the savannah, the dry forests and the semi-desert scrubs.

« During the course of history, humanity has learned to adapt its life and its activities to these arid and semiarid conditions. In the fields of agriculture, and particularly pastoralism, there are many instances where man and his activities are perfectly adjusted to these conditions. But during the last century, the population living in these areas has increased enormously and resources have become increasingly stretched and previously tried solutions have not proved suitable for solving many of the present problems. It is even possible to say that, in many cases, agriculture is not able by itself to maintain properly the equilibrium of the economy and of the country. In many countries, the problem of water resources remains crucial and knowledge of these resources is essential, particularly the amounts of precipitation (including condensation), surface water and groundwater, which can be utilized (either separately or combined) to the maximum benefit, even if these resources appear ridiculously small upon first examination ». This plea for greater knowledge of the water resources of arid zones is even more

urgent now than it was ten years ago. Of course, if we are to discuss the arid zone, we must be able to define its extent.

One of the most widely used methods was devised within the framework of the UNESCO MAB Programme. This method employs the ratio of the measured precipitation to the estimated potential transpiration computed by the Penman (1948) method. A version of this approach adopted by UNEP is shown in Table 1 and it indicates clearly the extent of the areas of the world involved. They range from the rainless dry rocks or shifting sands of the eastern Sahara to the semi-desert scrub that surrounds most deserts. In some regions differences of relief are very important, because there are locally important sources of water in the higher areas. In others, the water resources are dependent on the juxtaposition of mountains and on the rivers which drain these areas and cross the dry lands.

JEAN RODIER AND WMO

Jean Rodier was most closely associated with Orstom, and it was in the context of that agency's work in overseas countries that he developed his great knowledge and sensiti-

Addressing arid zone problems 115

Table 1 Aridity zones by PI PET ratios.

Climate zone R = PI PET ratio % of world covered

Hyper-arid R < 0.05 7.5 Very limited human activity around oases

Arid 0.05 R< 0.20 12.5 Pastoralism is possible but highly susceptible to interannual climate variability or groundwater resources

Semiarid 0.20/? < 0.50 17.5 Sustainable pastoralism. Agriculture susceptible to high degree of interannual climate variability

Dry sub-humid 0.50/? < 0.65 9.9 Wide range rain fed agricultural activities practised

vity to the problems of undertaking hydrological work in developing countries. It is not surprising, therefore, that he found a natural outlet for these concerns within the frame­work of WMO's international activities in hydrology. In the 1960s there was conside­rable debate as to the nature and extent of these activities and Jean Rodier was amongst those who championed the cause of a stronger role for WMO in the field. France designated him as a member of what was initially called the Commission on Hydro-logical Meteorology and which is today the Commission for Hydrology (CHy). In 1961, the First Session of the Commission elected him to chair the Working Group on Network Design: one of the basic topics of concern to the Commission at that time, and still one on which much remains to be done, both as regards the theory and the practice.

When plans for WMO's participation in the International Hydrological Decade (IHD) were being made, J. A. Rodier (France) was named to serve on the Panel of Experts established by the WMO Executive Committee to oversee WMO's contributions to the Decade.

For the Second Session of CHy, which was held in Warsaw in 1964, Jean Rodier chaired one of the two committees established to conduct the business of the meeting. Subsequently, CHy appointed him chairman of the Working Group on Representative and Experimental Basins, thus drawing on another of his fields of expertise and establishing another link to the IHD. He was re-appointed to chair the same Working Group at the Commission's third session in 1968, and again at its fourth session in 1972. When he finally relinquished the position in 1976, he had been chairing CHy working groups for 15 consecutive years.

Of equal, if not greater importance, was his election as Vice-President of the Commission for the period 1968 to 1972. As Vice-President of CHy, Jean Rodier played an important part in the convening of the Technical Conference of Hydrological and Meteorological Services (Geneva, 1970). This Conference brought together the heads of the world's Hydrological Services to discuss the co-ordination of their activities and how WMO might assist in this task. It made a number of recommendations for strengthening the role of hydrology in WMO which, in due course, led to a number of decisions that were taken by the Seventh World Meteorological Congress in 1975. Principal amongst these was an amendment to the basic legal document of the

116 A. J. Askew & J. C. Rodda

Organization; the WMO Convention, so as to include hydrology more clearly as part of the remit of the Organization. Over more than a decade, therefore, Jean Rodier worked to give hydrology a sound basis within WMO and it is to his credit that this basis has served so well over the subsequent two decades. These and similar events are recorded in the report of the Silver Jubilee of the Commission for Hydrology that was celebrated in July 1986 (WMO, 1986).

Other WMO activities where Jean Rodier played a significant part are less well documented. This is because in many of them he was more the facilitator than the principal actor. In particular: he facilitated the participation of Orstom staff in inter­national programmes, as well as the participation of hydrologists from other agencies in France and that of hydrologists from other French-speaking countries in various aspects of the WMO Hydrology and Water Resources Programme. Through these means, his contribution to WMO was very broadly based. The activities of working groups, the proceedings of workshops and symposia and the contents of various publications benefitting from an input by Jean Rodier, or originating with him. Strangely, he was the author of only one WMO publication, in fact the co-author (with Max Beran) of a joint WMO-UNESCO publication on hydrological aspects of drought (Beran & Rodier, 1985).

DROUGHT

Recently published statistics for the period 1963 to 1992 (DHA, 1994) indicate that drought, taken world-wide, is one of the worst of natural disasters globally (Fig. 1). They also show that it is very important in vulnerable regions, such as western Africa (Fig. 2), where drought causes more damage and affects more people than any other type of disaster.

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Addressing arid zone problems 117

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Fig. 2 Major disasters by region, 1963-1992, western Africa (% of significant disasters by type and category) (DHA, 1994).

Of course, as Beran & Rodier (1985) and many others have pointed out, there is great difficulty in defining drought. Definitions of drought abound, one starting point being: prolonged absence or marked deficiency of precipitation (UNESCO/WMO, 1992). Beran & Rodier (1985) quote six versions of the definition of hydrological drought (Table 2) and there are many others falling under headings such as « meteorological drought » and « agricultural drought ». Severity may vary throughout a

Table 2 Types of hydrological drought (Beran & Rodier, 1985).

1 A three-week to three-month runoff deficit during the period of germination and plant growth. This could be catastrophic for farming that is dependent upon irrigation drawn directly from the river without the support of reservoirs.

2 A minimum discharge significantly lower or more prolonged than the normal minimum but not necessarily advanced much in its position relative to the growing season. Because the germination period is not affected this type of drought is of less consequence to agriculture.

3 A significant deficit in the total annual runoff. This affects hydropower production and irrigation from large reservoirs.

4 A below normal annual high water level of the river. This may introduce the need for pumping for irrigation. This type of drought is related to Type 3 - deficit in annual runoff.

5 Drought extending over several consecutive years as with the « Secas » of northeast Brazil. Discharge remains below a low threshold or the rivers dry up entirely and remain dry for a very long time.

6 A significant natural depletion of aquifers. This is difficult to quantify because observation of the true level of the aquifer is disturbed by the over-utilization of groundwater during the drought.

118 A. J. Askew & J. C. Rodda

drought and hydrological processes may act to maintain the drought: the phenomenon of persistence which has been found in many time series, but not in all of course. There are variations in space during a drought, as well as in time, a factor which makes droughts more difficult to characterise than floods, for example. Spatial heterogeneity is one reason why drought intensity is frequently presented in the form of maps of rainfall depth, or rainfall deficiency, defined for example as the measured rainfall for the period as a percentage of the corresponding long term mean.

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Addressing arid zone problems 119

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Beran & Rodier (1985) gave attention to rainfall deficits, but they also looked at runoff deficiencies as a measure of drought. They investigated the return period of the mean annual discharge for selected rivers world-wide for the driest year during the 1960s and 1970s (Fig. 3). They also examined the variations in time of the ten highest and ten lowest flows for rivers in west and southern Africa (Fig. 4). In considering the relation between drought and climate change they stressed that, even under a different climatic regime, drought is expressed as a departure from normal.

DROUGHT AND CLIMATE CHANGE

Although Beran & Rodier (1985) did not dwell on the possibility that the African droughts of the 1970s and 1980s were indicative of climate change or that future changes

120 A. J. Askew & J. C. Rodda

in climate would alter the incidence of drought in Africa, this is something that others have considered. For example, Sircoulon (1991) has asked « Has there been a significant statistical change in the rainfall or discharge time series in the sahelian region during the last 100 years when global temperatures are observed to have increased? »

In considering this question, it is important to recognize that, quite apart from any question of climate change, the world faces a serious water crisis. We can but applaud the successes of modern hygiene and medicine which have led in the last few decades to a significant drop in the death rate, and hence to an unprecedented increase in the world's population. We must also recognize, however, that this means more people to provide with drinking water and greater demands for water for crop production so that those same people might have food to eat. Add to this the understandable aspirations of all peoples to improve their standard of living and we have the complication of increased demand for water per capitum. This is not only a problem of the quantity of water, but also the quality of water as pollution levels rise alarmingly, particularly in developing countries and newly independent states which do not have the resources to combat this threat.

The most recent studies reviewed in support of the work of the IPCC (Lang, 1995) note that these developments have made societies more sensitive and vulnerable to any variability in water supplies. The floods and droughts which, in the past, might have caused some inconvenience because a temporary high water levels or a shortage of water, now threaten the very lives of whole communities. Any change in climate would influence the hydrological cycle and very likely add an extra stress to this fragile situation. It is in this sense that the threat of climate change is so important for hydrology and water resources.

This threat is the greater in arid and semiarid areas because the very delicate balance of precipitation, évapotranspiration, infiltration and runoff is particularly sensitive to climate variations. The percentage of precipitation that runs off or infiltrates is much smaller than in other regions and can easily be reduced to zero as the result of a small, but significant, reduction in rainfall or an increase in temperature. Sircoulon (1990) has estimated that in the sahelian zone of west Africa the supply of water over the next few decades might vary by ±30-40%, but the demands on this supply are likely to increase by 250-500%!

It can be argued that hydrological modelling will clarify and even quantify the extent of such problems and threats, but here we face several serious problems.

First, the predictions of change in precipitation and temperature are not precise enough in space and time to allow us to interpret them in terms of changes in soil moisture, aquifer levels and streamflow.

Secondly, the great majority of hydrological models have been developed in temperate climates and, while the hydrological processes are the same the world over, their relative importance varies enormously and many models fail to truly represent the hydrological regimes of arid regions. For example, most of the classical models have great difficulty in reproducing the regimes of rivers which flow only intermittently after major rare storms and are dry for 90-95% of the time. Yet it is precisely such rivers as this which can be of greatest importance for the survival of societies in many regions of the world.

A third problem is that in the arid zone the networks of instruments and the measurements they make are amongst the poorest in the world, rarely reaching the

Addressing arid zone problems 121

standards recommended by WMO (1994). Consequently, we lack much of the data needed to characterize these areas hydrologically in the same manner as we do for many other parts of the globe (Rodda, 1995).

The call therefore is for more research on the hydrology of arid regions which would lead to a better ability to predict the potential impact of climate change, and more data from such regions to support this research.

Some skill has now been developed in making seasonal predictions of rainfall. These are in very general terms, but they are still in terms that can be of great value to those responsible for agricultural activities and water resources management. There are great hopes for further improvements in this regard but, as always, there is need for improved data and research efforts if these improvements are to be achieved. An interesting aspect of this is that the data needed, such as sea surface temperatures, must be collected over large areas, often far from the regions that can benefit from the forecasts. This presents a real challenge for international solidarity: one that we can hope the national agencies and international organizations involved will rise to with conviction.

While there is much variation in the various estimates of the impacts of climate change on the water balance of the regions of the world, something that seriously limits our ability to interpret them in terms of hydrological systems, there is fairly general agreement that the dry regions will become warmer, particularly in the higher latitudes, and hence more arid - a worrying prospect for those facing the dual problems of drought and desertification in these regions.

NATURAL DISASTERS

The United Nations has declared the 1990s as the International Decade for Natural Disaster Reduction (IDNDR). When one considers the nature of the major disasters around the world (see Fig. 1) it is clear why WMO has been so involved in the Decade since its very conception. What is more, the statistics clearly show that disasters of hydrological origin such as floods and droughts are responsible for two thirds of the persons affected and over half of the damage caused. Although they are listed as causing only one third of the deaths, one has to ask how many of those who died from epidemics or other medical causes did so because of their resistance was lowered as a result of starvation during droughts.

The danger of flooding in arid areas is often underestimated, or even ignored, because floods of any significant magnitude are so rare. Widespread flooding can occur, however, and can cause extensive economic damage, especially if the water lies on the ground for long periods during critical growing seasons for crops. Of greater danger to life, are the flash floods which are very difficult to monitor and to predict. Nevertheless, there is no doubt that the major threat in arid zones is that of drought. This is clearly demonstrated in the statistics for western Africa (see Fig. 2): a region with which Jean Rodier was particularly associated. This led WMO many years ago to establish the project entitled « Agrometeorology and operational hydrology and their applications (Agrhymet) », based in Niamey, and in more recent times, the Drought Monitoring Centres in Nairobi and Harare where efforts are now being made to interpret present meteorological condition and limited climate predictions in terms which can be used to minimize the impact of both meteorological and hydrological droughts.

122 A. J. Askew & J. C. Rodda

Again, the call is for data which can be used to sustain and improve the work of these centres and the will of government departments to act on their advice.

DESERTIFICATION

In recent years, the focus of attention has switched to the growing threat of desertifi­cation, with its links to famine and sustainable development. Although he did not use the word « desertification » himself, Rodier obviously included this process in his thinking about the arid zone. Had he used the word, undoubtedly he would have identified the problem of water resources as being crucial to desertification. This is in marked contrast to the recently agreed International Convention to Combat Desertification, where the drafters seemed to be largely unaware that absence of water resources is one of its prime causes. To a hydrologist, what could be more of an enigma?

In recent times, WMO has been working closely with the International Panel of Experts on Desertification that has been set up by the International Negotiating Committee for the Convention. The aim has been to introduce appropriate references in both the background documents and the action plans to water and to water resources. As a contribution to this effort, Jacques Claude, an Orstom expert, has prepared a report for WMO in which he notes that in fact the importance of water in the International Convention to Combat Desertification is masked by the fact that references to it are distributed throughout the text and are generally implicit in all activity areas. Water is certainly a renewable resource, but it is not the same as other natural resources: — it is not a resource which is directly productive (it is a non-biotic element), but it is

an indispensable factor in production and, in arid zones, the primary factor limiting biological production;

— it does not in itself offer the potential for economic development, but provides the necessary conditions for the development and exploitation of biological resources;

— it is not available everywhere and in each location, its spatio-temporal distribution being discrete. It is therefore necessary to manage its distribution, even to modify it, in order to make rational use of it in arid zones, it is often a factor in the degradation or destruction of bio-productive resources or their infrastructure (soil erosion, salinization, flooding ...);

— it is also a reservoir and vehicle for the dissemination of so-called "water-borne diseases" which at one stage or another in their development pass through water. This is a major factor in health risk. It is therefore also necessary to control its harmful powers (Claude, 1995) There is evidence that desertification is spreading, the process that sparked the

Convention and the process which the Convention seeks to halt and reverse. This is because the already difficult conditions in the arid zone have been exacerbated by the recurring and protracted droughts of recent years, rendering ineffective the indigenous methods of adaption employed traditionally during droughts.

Desertification is now a direct threat to over 250 million people across the world, and an indirect threat to a further 750 million (Williams & Balling, 1994). The UN Conference on Environment and Development held in Rio de Janeiro in 1992 defined desertification as « land degradation in arid, semiarid and dry sub-humid areas resulting from various factors, including climate variations and human activities ».

Addressing arid zone problems 123

At the time of the UN Conference on Desertification (UN, 1977) the view was that desertification was principally the result of poor management of land and human resources. The call was for the governments concerned to take account of the fragility of the land in such regions and to implement policies, particularly those concerning farming and grazing techniques and the movement of populations, so as minimize the threat to these lands. In 1977 little was said about the possibility of « natural causes » for desertification and there was no doubt that the emphasis was then on governments to accept the major responsibility.

This was before the recent great interest in climate and climate change. The pendulum can easily swing the other way, of course, and governments can point to climate change as the real cause - a tempting option as it would allow them to abrogate their responsibility in the matter.

It would appear that the truth lies somewhere in between and current thinking is to give clear recognition to the importance of climate variability and, if proven also to, climate change, in the whole process but to recognize that there is little we can do at the local scale to prevent this and so governments and local communities should continue and strengthen their efforts to halt the processes of desertification.

The interaction between desertification and climate is a close and complex one. There is always the possibility of desertification influencing the climate, but it is generally agreed that the influence is local rather than continental or global in nature. On the other hand, there is no doubt that climate is one of the main factors affecting desertification.

Climate has a major impact on soils, vegetation and water resources in dry lands and consequently on land use. The soils in these regions are inherently vulnerable to deserti­fication processes because of the sparse vegetation and low levels of organic matter. The result is a great vulnerability to erosion by wind and by water.

Lack of knowledge here, as everywhere, is one of the limiting factors in combating desertification and it is important that not only more research is undertaken, but that national agencies in the regions concerned maintain long-term programmes for monitor­ing desertification processes and the accompanying geophysical characteristics such as precipitation, temperature, radiation, soils moisture, groundwater levels and streamflow. Making such observations requires considerable capital investment and then a long-term commitment to the maintenance of the networks. This is expensive, far more expensive than is often taken into account at the outset. The result is that, all too often, monitoring programmes last only a few years or, in the case of developing countries, until external support is no longer available. This is one of the reasons why WMO and others are working to establish a World Hydrological Cycle Observing System (WHyCOS) (Rodda et al., 1993). Short records are of very limited value and there is a fundamental need for all countries in the world to establish and maintain adequate monitoring programmes of all factors of national importance. Knowledge is power - so we are told. Knowledge such as is referred to above gives governments the power to make the right decisions. The lack of data and hence of knowledge leaves the authorities without the power to control their own resources and hence their own destinies.

KNOWLEDGE BASE

The International Conference on Water and the Environment (Dublin, 1992) called for

124 A. J. Askew à J. C. Rodda

« fundamental new approaches to the assessment, development and management of fresh­water resources » and included in its « Action Agenda » a recognition of the importance of data and information under the heading:

« the knowledge base: measurement of components of the water cycle, in quantity and quality, and of other characteristics of the environment affecting water are an essential basis for undertaking effective water management. Research and analysis techniques, applied on an interdisciplinary basis, permit the understanding of these data and their application to many uses. With the threat of global warming due to increasing greenhouse gas concentrations in the atmosphere, the need for measurements and data exchange on the hydrological cycle on a global scale is evident. The data are required to understand both the world's climate system and the potential impacts on water resources of climate change and sea level rise. All countries must participate and, where necessary, be assisted to take part in the global monitoring, the study of the effects and the development of appropriate response strategies ». Arid countries, faced as they are with the threat of drought and desertification, should

see climate and water resources data as a national treasure to which they can add year by year, for a price surely, but at a very moderate price when one considers the cost of making wrong decisions in the face of such worrying threats to the life and safety of their populations.

Jean Rodier was a strong and articulate advocate of increasing our knowledge of water resources and hy drologicalprocesses, inparticular in arid zones. There canbe nobetter way of recognizing his contributions to the science and practice of hydrology than to strengthen the hydrologicalmonitoringnetworksandwaterresources studies in these zones, where the existence of life itself is so closely linked to the availability of such resources.

REFERENCES

Beran, M. A. & Rodier, J. A. (1985) Hydrological Aspects of Drought. WMO-UNESCO Panel Report, Studies and Reports in Hydrology, UNESCO Press, Paris.

Claude, J. (1995) Gestion de la resource en eau. WMO (draft of February 1995).

DHA (1994) Disasters around the world - a global and regional view. Information Papers no. 4, Department of Humanitarian Affairs, United Nations, New York.

Hare, F. K. & Ogallo, L. A. J. (1993) Climate Variations, Drought and Desertification. WMO, Geneva.

Lang, H. (1995) Personal communication.

Penman, H. L. (1948) Natural evaporation form open water, bare soil and grass. Proc. Roy. Soc. Lond. A193,120-146.

Rodda, J. C , Pieyns, S. A., Sehmi, N. S. &Matthews, G. (1993) Towards a world hydrological cycle observing system. Hydrol. Sci. J. 38(5), 373-378.

Rodda, J. C. (1995) Guessing or assessing the worlds water resources. / . Chart. Instn Wat. Environ. Manage. 9,360-368.

Rodier, J. A. (1985) Aspects of arid zone hydrology. Chapter 8 in: Facets of Hydrology II(ed. par J. C. Rodda), 205-247. Wiley, Chichester, UK.

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