Water scarcity already affects large parts of the world

Flickr/suburbanbloke

Climate change will affect the water security of developing countries. Lucinda Mileham explores their priorities as they struggle to cope.

Freshwater is a scarce resource. Only 2.5 per cent of the 1.4 billion km³ of water on Earth is freshwater fit for human consumption, and most of this is inaccessible — nearly 70 per cent is locked up in glaciers, snow and ice. Our greatest source of freshwater is the 8 million km³ of groundwater, with only 0.3 per cent of freshwater (105,000 km³) being found in rivers, streams and lakes. [1]

Discussions about freshwater availability increasingly focus on water security, which refers to people's access to enough safe and affordable water to satisfy their needs for household use, food production and livelihoods. [2]

Water insecurity can arise from physical scarcity, resulting either from climatic or geographical factors, or from unsustainable consumption or overexploitation. It can also have economic origins, with poor infrastructure or capacity preventing access to the water resources available, or occur where pollution or natural contamination renders water resources inaccessible.

Water insecurity and scarcity already affect large parts of the developing world. The past century has seen a sixfold increase in global water demand. Nearly three billion people (about 40 per cent of the global population) live in areas where demand outstrips supply. [2] 

Figure 1: Areas of the world already facing water scarcity full-size image (131kB)

Adapted from [2]

This situation is set to worsen in the coming decades as populations grow, economies develop and agriculture and industry expand.

Climate change has already affected water resources across the world. It has, for example, increased the global mean sea level by 1.75 mm each year in the second half of the twentieth century, [3] caused the widespread retreat of non-polar glaciers, reducing dry-season water flows, and increased borehole and marine temperatures.

Solar energy trapped in the atmosphere by greenhouse gases drives the hydrological cycle, so any increase effectively intensifies the cycle, changing rainfall patterns and exacerbating extreme events such as droughts and floods.

The effects of climate change on water security can already be seen. Globally, the area of land classified by the IPCC as 'very dry' has more than doubled since the 1970s. [4] This has been accompanied by greater flooding in the mid-high latitudes, longer and more frequent droughts in parts of Asia and Africa, and more frequent and intense El Niño events — all of which change the balance between demand and supply of water resources.

Water security in the developing world is particularly vulnerable to the impacts of climate change, partly because their locations mean these nations feel the brunt of climate change, partly because their low incomes and poor institutional capacity limit their ability to cope with changing water supplies, and partly because they rely heavily on water-based industries, such as agriculture.

In Africa, higher temperatures, increased evaporation and lower rainfall have combined to reduce water flow by up to 40 per cent in many major rivers and caused recurrent drought in the Horn of Africa (see Figure 2). [5,6]

Figure 2: Climate-change vulnerabilities and impacts in Africa, many of which are driven by changing water resources full-size image (190kB)

Anna Ballance, UNEP/GRID-Arendal, 2002

Box 1: Uncertainty

The biggest problem in assessing the future impacts of climate change on water security is the uncertainty of predictions. This uncertainty arises from the internal variability of the climate system, uncertainty in future emissions and development scenarios, uncertainty in the way models translate these emissions into climate change, and questions over the accuracy of hydrological models. [7]

Climate modelling usually uses global circulation models (GCMs) with coarse resolution (more than 150 km²), but in some regions the uncertainty in climate simulations is so great that no clear sign of change can be given, raising serious questions over the relevance of these data to projecting changes in regional hydrology.

Regional climate models (RCMs) with finer resolution (less than 50 km²) can provide more robust input data for hydrological models. These models have improved greatly since the early 1990s, but relatively few have been developed for, or applied to, the developing world.

A lack of field data is a major obstacle to regional climate modelling

Wikimedia Commons/Babakathy

One major obstacle to regional climate modelling is a lack of the high-quality field data needed to validate such models.Reliable information on local and regional meteorological parameters, such as precipitation, evaporation and temperature, are needed for water-balance models and forecasting.

In many developing regions, field observations are extremely sparse or not available. Significant improvements in monitoring networks for validating regional climate models are urgently required to improve our understanding of the climate system and the impacts of climate change on water resources.

However, temperatures will almost certainly rise — model predictions for a range of emission scenarios suggest an increase in global temperatures of 1.1–6.4 degrees Celsius by the end of the century. [4]

And, according to the IPCC, there is abundant evidence that freshwater resources could be strongly affected by climate change (see Table 1).

Table 1: Climatic changes predicted by the IPCC, and how they are expected to affect water availability, accessibility and use (compiled from data in reference [4] and [7]).

In 2008, the IPCC predicted with high confidence that the negative effects of climate change on water resources would outweigh the benefits, with the area subject to increasing water stress by the 2050s being more than double that facing decreasing water stress. [7]

Such water insecurity can have devastating effects on a country's economic prosperity and the well-being of its citizens (see Box 2).

Actions to mitigate climate change by reducing the levels of greenhouse gases in the atmosphere will be essential in the long term. But climate change is already happening, and even if mitigation efforts could immediately reduce carbon emissions to zero, water supplies would already be affected.

Treadle pumps tap groundwater for small-scale irrigation

Flickr/Mukul Soni

Fortunately, this does not necessarily require new technologies. Water managers use a range of tools to cope with variability in water supplies, from high-tech, high-cost desalination plants, which turn sea water into drinking water, to traditional, low-cost treadle pumps that tap groundwater for small-scale irrigation (see Table 2).

Box 3: Integrated strategies for improving water security

High-cost case study: Saudi Arabia

Saudi Arabia relies exclusively on rainfall, groundwater and desalinated seawater to meet water demands that, in 2000, stood at 17,320 million cubic metres (MCM).

Saudi Arabia's desalination plants cost an estimated US$10 billion

Flickr/Waleed Alzuhair

Groundwater resources in the country are plentiful — more than 2,000 billion cubic metres — but they recharge very slowly, at just 2,763 MCM each year. Extensive extraction and ineffective management of these resources has led to falling water tables and a decrease in water quality.

In the 1990s the government realised it needed to protect and conserve water resources. It began encouraging modern and efficient irrigation systems, changing cropping subsidies, implementing water tariffs, controlling leakage, building dams and desalination plants, and recycling treated wastewater.

These measures limited the excessive use of fossil groundwater, reduced environmental degradation, encouraged water conservation and created a strong framework for coping with water stress.

But they were not cheap — the country's 35 desalinisation plants alone are estimated to have cost US$10 billion.

Low-cost case study: Ghana

In contrast, Ghana has focused on traditional low-cost practices to cope with the water insecurity induced by climate change. Today, Ghana receives 20–30 per cent less rainfall than 40 years ago. In the Offin basin, small-scale farmers have also faced more variable rainfall, up to 45 per cent less river flow, and wells drying up, causing yields to fall and crops to fail.

To cope, families have started re-using wastewater for irrigation, adopted traditional rooftop rainwater-harvesting techniques, and replaced traditional 'thirsty' crops, such as cocoa, with more drought-resistant crops, such as cassava. Local authorities also distribute affordable filters to improve water quality, and have begun fining people found clearing the vegetation alongside rivers and streams to prevent siltation and low flows.

Thousands of small reservoirs and ponds have been built to supply water for domestic use, livestock and small-scale irrigation. The government actively promotes community ownership and management of water resources, providing training and financial aid, and encouraging the use of traditional communication techniques to educate communities about water use, conservation and development.

The extent to which countries can adapt to increasing water insecurity is influenced by several factors. First, there may be a physical limit to adaptation — for example, it may be impossible to adapt where rivers dry up completely.

Finally, the capacity of water management agencies may pose institutional limits. Many developing countries suffer from a lack of coordination between agencies and sectors, ineffective water governance, and a poor skills base.

The first is the need to prioritise the management of water resources. This may seem obvious, but many countries have no long-term water policies. Policies will need to integrate all the sectors that rely on water, from agriculture and fisheries to manufacturing and municipal water use.

Improving watershed and resource management is also vital. The IPCC has advocated integrated water-resources management as a framework for adapting to climate change across socioeconomic, environmental and administrative systems.

Involving local stakeholders and promoting community-based approaches is essential to ensure that adaptation options are taken up and achieve long-lasting results. This requires a better understanding of water-based livelihoods in the developing world and their vulnerability to climate-related hazards and the impacts of water security on food and livelihood security.

Addressing gaps in our knowledge about climate change and water is also a priority. Field data are sparse and, in many cases, observational networks are shrinking. The IPCC has highlighted the "need to improve understanding and modelling of climate changes related to the hydrological cycle at scales relevant to decision-making". [7] It also says that information about the water-related impacts of climate change is inadequate.

Without further investment in data collection and knowledge building, the uncertainty associated with predicted changes will remain high, and estimates of hydrological change will remain inaccurate. Until we can better predict the change, we will be poorly equipped to plan for the future.