Adaptation Options in the Water Sector

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Adaptation to changing conditions in water availability and demand has always been at the centre of water management. Typically, it is assumed demand will grow and that the natural resource base is constant, except where land-use change occurs (Kundzewicz et al. 2007). Conventionally, it is also assumed that the future resource base will be similar to that of the future. Given the inevitability of climate change, this assumption is incorrect. Scenarios of future conditions vary and are not detailed. The IPCC (2007a) point to decreasing water availability in mid-latitudes semi-arid low latitudes and increased water availability in moist tropics and high latitudes. Annual average river runoff and water availability are projected to increase by 10-40% at high latitudes and in some wet tropical areas, and decrease by 10-30% over some dry regions at mid-latitudes and in the dry tropics, some of which are presently water-stressed areas (IPCC 2007b).

Climate processes powered by solar energy drive the hydrological cycle that determines the global distribution of water resources. The key question for those involved in planning and investment in the water sector is: if the climate warms in the future, will the water cycle intensify and what will be the nature of that intensification? A number of studies have addressed this question. To see how rainfall had changed with the 0.4°C global warming of the past 20 years, Wentz et al. (2007) analysed data collected by US weather satellites from 1987 to 2006. According to the results of this work, global warming will increase precipitation globally by three times the amount predicted by climate models. Wentz et al. (2007) state it impossible to predict where additional precipitation will fall; wet areas may get wetter, but drought-prone regions might also get some relief. Huntington (2006) reviewed the findings from more than 100 scientific studies that assessed trends in hydrologic variables, including precipitation, runoff, tropospheric water vapour, soil moisture, glacier mass balance, evaporation and evapotranspiration. According to Huntington, although data are not complete, and sometimes contradictory, the weight of evidence indicates an ongoing intensification of the water cycle, but the results of the work show no increase in storms or floods. Smith et al. (2006) reviewed variations in annual global precipitation for the period 1979-2004 and found that "trends have spatial variations with both positive and negative values, with a global-average near zero". This is reflected in global precipitation anomalies over the long period from 1900 to 2005 (Fig. 9.1). Based on these findings it would seem water managers have little to go on. But this might not be the case. Water management is based on minimization of risk and managers are accustomed to adapting to changing circumstances, including extreme climatic events, many of which can be regarded as analogs of future climate.

A wide range of adaptive options are available to water managers faced with changing circumstances. One widely used classification distinguishes between

Fig. 9.1 Annual global precipitation anomalies for the period 1900-2005. (NCDC, NOAA: 'Climate of 2005 - Annual Report' 2006)

"supply-side" and "demand-side" options. Examples of supply-side options are: prospecting and extraction of groundwater; increasing storage capacity by building reservoirs and dams; expansion of rain-water storage; water transfer; desalination of sea water; and removal of invasive non-native vegetation from riparian areas. Examples of demand-side options are: improvement of water-use efficiency by recycling water; reduction in water demand for irrigation by changing the cropping calendar, crop mix, irrigation method, and area planted; reduction in water demand for irrigation by importing agricultural products, i.e., virtual water; promotion of indigenous practices for sustainable water use; expanded use of water markets to reallocate water to highly valued uses; and expanded use of economic incentives including metering and pricing to encourage water conservation (Kundzewicz et al. 2007).

Supply-side options focus on increasing capacity, while demand-side options focus on managing demand and changing institutional practices and operating rules for existing water resource systems. From the supply side, even now fresh water shortages occur virtually everywhere from time to time. Any change in local weather patterns driven by changes to global climate processes will have direct effects on water availability, but it will also have unpredictable indirect social and economic regional effects, such as impacts on agricultural productivity, availability of renewable hydroelectric power and supply of municipal water. From the demand side, agriculture and industry are the major users of water globally. Population growth, agricultural expansion, and demand for water by an expanding the industrial sector are likely to make water shortages even more prevalent in coming years.

Another classification scheme proposed here distinguishes between (1) technological, (2) behavioural, (3) economic and (4) legal adaptive measures to manage and extend water resources. The following sections summarise these adaptive options. It assumes that the relative merits of one adaptive technique over another can be characterized in terms of the benefits and costs of the adaptation, across a spectrum of no effect ("no adaptation" or "wrong choice of adaptation") to perfectly effective ("adaptation sufficient to eliminate all effects of climate change") at an optimal level of cost effectiveness. There is also the issue of conflicting choices.

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