Arid and semi-arid regions present special challenges for water management. They are, by definition, areas where water is at its most scarce, and face great pressures to deliver and manage freshwater resources. Demand for water has increased dramatically, due to population growth, increasing expectations for domestic water use, and expansion of industrial and agricultural activities. Available water resources have been reduced by pollution and over-abstraction. Many of the world's arid regions are further threatened by climate change. In addition, the science base to support water management remains limited. Hydrological processes can be very different from those of humid regions, precipitation and flow exhibit extreme variability in space and time, and data are often restricted in spatial coverage, record length and data quality.

UNESCO has identified, within the International Hydrological Programme, a special need to exchange knowledge on scientific aspects of water resources (with respect to both quantity and quality) in arid and semi-arid lands, and is supporting a number of regional centres to promote exchange of information and dissemination of good practice. At the global level, UNESCO has initiated G-WADI, a Global network for Water and Development Information for arid lands. Information on G-WADI products and a news-watch service can be found on the G-WADI website (www.gwadi.org). G-WADI aims to facilitate the global dissemination of state-of-the-art scientific knowledge and management tools, and to facilitate the sharing of scientific and technical knowledge and management experience of new and traditional technologies to conserve water.

GROUNDWATER RESOURCES, GROUNDWATER MODELLING AND THE QUANTIFICATION OF RECHARGE

The traditional development of water resources in arid areas has relied heavily on the use of groundwater. Groundwater uses natural storage, is spatially distributed and, in climates where potential evaporation rates can be of the order of metres per year, provides protection from the high evaporation losses experienced by surface-water systems. Traditional methods for the exploitation of groundwater have been varied, including the use of very shallow groundwater in seasonally replenished riverbed aquifers (as in the sand rivers of Botswana), the channelling of unconfined alluvial groundwater in afalaj (or qanats) in Oman and Iran, and the use of hand-dug wells. Historically, abstraction rates were limited by the available technology, and rates of development were low, so that exploitation was generally sustainable.

However, in recent decades, pump capacities have dramatically increased and hence agricultural use of water has grown rapidly, while the increasing concentration of populations in urban areas has meant that large-scale well fields have been developed for urban water supply. A common picture in arid areas is that groundwater levels are in rapid decline; in many instances this is accompanied by decreasing water quality, particularly in coastal aquifers where saline intrusion is a threat. Associated with population growth, economic development and increased agricultural intensification, pollution has also become an increasing problem. The integrated assessment and management of groundwater resources is essential so that aquifer systems can be protected from pollution and over-exploitation.

INTRODUCTION

Groundwater quality issues now assume major importance in semi-arid and arid zones, since scarce reserves of groundwater (both renewable and non-renewable) are under threat due to accelerated development as well as a range of direct human impacts. In earlier times, settlement and human migration in Africa and the Middle East regions were strictly controlled by the locations and access to fresh water mainly close to the few major perennial rivers such as the Nile, or to springs and oases, representing key discharge points of large aquifers that had been replenished during wetter periods of the Holocene and the Pleistocene. This is a recurring theme in writings of all the early civilisations where water is valued and revered (Issar,1990). The memory of the Holocene sea-level rise and pluvial periods is indicated in the story of the Flood (Genesis 7:10) and groundwater quality is referred to in the book of Exodus (15:20). More recent climate change may also be referred to in the Koran (Sura 34:16).

In present times, groundwater forms the primary source of drinking water in arid and semi-arid regions, since river flows are unreliable and large freshwater lakes are either ephemeral (e.g. Lake Chad) or no longer exist. The rules of use and exploitation have changed dramatically over the past few decades by the introduction of advanced drilling technology for groundwater (often available alongside oil exploitation), as well as the introduction of mechanised pumps.

INTRODUCTION

As a result of the ever-growing global population, pressure on water resources is increasing continuously, above all in arid and semi-arid regions. In many cases, the presently applied management practices are non-sustainable and lead to serious water-related problems such as the depletion of aquifers, the accumulation of substances to harmful levels, to water conflicts or economically infeasible costs. In this contribution, we illustrate these problems with several case studies. The northwest Sahara aquifer system is used to show the consequences of the overpumping of aquifers. A typical upstream–downstream problem is discussed with the example of the Okavango delta. Another case study discussed is the Yanqi basin in China. The Yanqi basin is a typical example showing how inappropriate irrigation practices can lead to soil salinisation and ecological problems of the downstream. Possible solutions to these problems and the role of numerical modelling as a tool to develop sustainable management practices are discussed. Some of the most common problems in setting up reliable models are highlighted and ideas how to address these problems are given. In the last part of this chapter, we discuss strategies to close the existing gap in thinking between scientists and decision makers.

DEFINITION OF SUSTAINABLE WATER MANAGEMENT

In a pragmatic definition, sustainable water management describes a practice which prevents irreversible damage to the resource water and resources related to it such as soils and ecosystems and which preserves in the long-term the ability of the resource to extend its services (including ecological services).

INTRODUCTION

Groundwater is a particularly vital resource in arid and semi-arid areas owing to the scarcity of suitable surface-water resources and the high evaporation from surface-water storage. However, if it is also to be a reliable resource, able to meet current and future demand, it has to be managed effectively, not only in terms of quantity (i.e. abstraction) but also quality. Recent decades have seen substantial progress in the development of methods for remediating contaminated groundwater (Reddy,2008). However, because of the complexities associated with the removal and/or destruction of pollutants in the subsurface this is often both costly and time consuming. The maxim ‘prevention is better than cure’ is therefore an important one in groundwater resource management.

One of the key instruments for seeking to maintain good groundwater quality is groundwater protection policy. In most developed countries groundwater protection has been formally incorporated into legislation as a means to ensure good groundwater quality on a sustainable basis and as part of an integrated approach to environmental protection (e.g. EU, 2009). In practice, this is achieved through aquifer vulnerability mapping at the regional scale and source zone protection at the scale of local abstractions. This chapter summarises these two complementary approaches to groundwater protection and considers how they can be implemented in arid and semi-arid regions. This focus on climate is important, as the geological and hydrological conditions are generally very different from those in more temperate regions (Robins et al., 2007).