Hydrogeology. Kevin M. Hiscock

10⁶ m³ a⁻¹ (Zektser and Everett 2004). By the 1970s, in the Ouargla Oasis of northern Algeria, there were approximately 2000 boreholes developed in the NWSAS in order to irrigate date palms (see Plate 1.6). In southern Tunisia, exploitation of the Complex Terminal aquifer increased from 9 × 10⁶ m³ a⁻¹ in 1900 to about 190 × 10⁶ m³ a⁻¹ in 1995. The impact of this intensive development on the aquifer system has been observed in discharge areas. In Algeria, the flow of springs decreased from 200 L s⁻¹ in 1900 to 6 L s⁻¹ in 1970, whereas in Tunisia, the flow from springs decreased from 2500 L s⁻¹ in 1900 to virtually nil (less than 30 L s⁻¹) in 1990 (Zektser and Everett 2004). Traditional irrigation methods in the region used sustainable quantities of water, but the more intensive modern irrigation methods used at present have led to a degraded water quality, decreased water levels and loss of artesian pressure, as well as salinization of the superficial water table and soil zone due to the drainage conditions. This salinized water is typically at a depth of 0.5–1.5 m below the soil surface and is detrimental to date palms (UNEP 2008).

      1.6.1 Global groundwater abstraction

With rapid population growth, groundwater abstractions have tripled over the last 40 years (Fig. 1.11), largely explained by the rapid increase in irrigation development stimulated by food demand in the 1970s and by the continued growth of agriculture‐based economies (World Bank 2007). Emerging market economies such as China, India and Turkey, which still have an important rural population dependent on water supply for food production, are also experiencing rapid growth in domestic and industrial demands linked to urbanization. Urbanized and industrial economies such as the European Union and the United States import increasing amounts of ‘virtual water’ (Allan 1998, 2003) in food (see Box 1.4) and manufactured products, while water use in industrial processes and urban environments has been declining, due to both technological changes in production processes and pollution mitigation efforts (WWAP 2009).

Fig. 1.11 1960–2000 trends in total global water demand (right axis, indexed for the year 2000), global groundwater abstraction (left axis, km³ a⁻¹) and global groundwater depletion (left axis, defined as groundwater abstraction in excess of groundwater recharge in km³ a⁻¹) for sub‐humid and arid areas (Wada et al. 2010).

      (Source: Wada, Y., vanBeek, L.P.H., vanKempen, C.M. et al. (2010). Global depletion of groundwater resources. Geophysical Research Letters 37, L20402, 5 pp. © 2010, John Wiley & Sons.)

Table 1.3 shows that three countries, India, China and the United States, are estimated to abstract in excess of 100 km³ a⁻¹ of groundwater and that several countries, including Pakistan, Saudi Arabia, Syria, India, Iran and Bangladesh, use greater than 86% of groundwater abstraction for irrigation, while Indonesia, the Russian Federation and Thailand use greater than 60% of groundwater abstraction for domestic use. Also, Saudi Arabia, Bangladesh, Syria and Iran abstract more than 57% of their total freshwater demand from groundwater.

In regions of the world where the rate of groundwater abstraction exceeds the rate of natural groundwater recharge over extensive areas and for long time periods, over‐exploitation or persistent groundwater depletion is the consequence. As shown by the global overview of Wada et al. (2010), in the year 2000, the rate of total global groundwater depletion is estimated to have increased to 283 km³ a⁻¹ (Fig. 1.11). Groundwater depletion rates were found to be highest in some of the world's major agricultural regions including north‐east Pakistan and north‐west India, north‐east China, the Ogallala aquifer in the central United States (see Section 10.2.1), the San Joaquin aquifer in the Central Valley of California (see Box 2.7), Iran, Yemen and south‐east Spain.

Table 1.3 Countries with estimated groundwater abstraction greater than 10 km³ a⁻¹ (Margat and van der Gun 2013).

      (Source: Adapted from Margat, J. and van der Gun, J. (2013) Groundwater Around the World: A Geographic Synopsis. CRC Press/Balkema, EH Leiden.)

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Country	Estimated groundwater abstraction (km^3 a^−1)	Groundwater abstraction by sector	Groundwater share of total freshwater abstraction (%)
Irrigation (%)	Domestic use (%)	Industry (%)
India	251.00	89	9	2	33
China	111.95	54	20	26	18
United States of America	111.70	71	23	6	23
Pakistan	64.82	94	6	0	32
Iran	63.40	87	11	2	57
Bangladesh	30.21	86	13	1	79
Mexico	29.45	72	22	6	35
Saudi Arabia	24.24	92	5	3	95
Indonesia	14.93	2	93	5	11
Turkey	13.22	60	32	8	16
Russian Federation