Ingeniero

Chapter 5

Demand Forecasting

Abstract Many hydrological forecasting applications require an assessment of water demand as well as water supply, and demand forecasts can require consideration of the water requirements for a wide range of applications. Examples include the availability of raw water for irrigation, hydropower generation and industrial water supply, and of treated water forpublic water consumption. Some applications, such as hydropower generation, may only store water temporarily, returning it to river flows at a later time (with minor evaporation and seepage losses), whilst other demands can represent a permanent loss to the river system. Forecasts also often need to provided at a range of timescales, from short-term values for tactical decision making, through toseasonal and longer term values for strategic planning. This chapter discusses a range of techniques for estimating and forecasting water demand, with applications in water supply, irrigation and power generation. Some typical approaches to decision making are also introduced, with a more detailed discussion in later chapters. Keywords Abstractions · Demands · Discharges · Demand forecast · Watersupply · Agriculture · Irrigation · Power generation · Hydropower · Thermoelectric

5.1 Introduction
In many hydrological forecasting applications, it is important to consider the abstractions and discharges by key water users, particularly under low flow conditions. This can require an understanding of the likely demands for water across a range of applications, including water supply, agriculture,and power generation, and of return flows or discharges of treated water and effluent/waste-water. The need to include these influences will depend on the magnitude of the artificial component of the flows, compared to main river flows and other parameters of interest, such as reservoir volumes. For example, in flood forecasting applications, these influences may be relatively small compared to floodflows, and are often ignored (although can be important for
K. Sene, Hydrometeorology, DOI 10.1007/978-90-481-3403-8_5, C Springer Science+Business Media B.V. 2010 141

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5 Demand Forecasting

forecasting the onset of an event) whilst, for forecasting during drought conditions, they can be crucial to consider. Later chapters include several examples of operational systems which includeforecasts for abstractions and discharges, including drought forecasting models (Chapter 8) and water resources models (Chapter 11). The underlying techniques typically include supply-demand models, integrated catchment models, and distributed models. As discussed in Chapter 4, supplydemand models maintain a water balance throughout the simulation, whilst integrated catchment models typically combinerainfall-runoff, flow routing and other modeling components, and distributed models use physically-based equations for rainfall-runoff and other processes, and operate on a gridded basis. Other artificial influences on flows may also need to be considered, such as from reservoirs, sluices, barriers and other structures, and this topic is discussed in Chapter 9. The potential uses of water are many andvaried, and the volumes of water required can also vary widely. Table 5.1 shows some examples of the major types of river abstractions and discharges which can occur, and the potential impacts on river flows. For example, for England and Wales, which covers an area of approximately 150,000 km2 with a population of more than 50 million people, the Environment Agency manages about 20,000 abstractionlicences (Environment Agency 2008a). Approximately 50% of freshwater (i.e. raw water) abstractions are for public water supply, and about 30% are used to support electricity generation (Fig. 5.1). In the USA, estimates for the year 2000 under the categories of public supply, domestic (self-supplied), irrigation, livestock, aquaculture, industrial, mining, and thermoelectric-power suggested that...