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As populations increase and development calls for increased allocations of groundwater and surface water for the domestic, agricultural, and industrial sectors, the pressure on water resources intensifies, leading to tensions, conflicts among users, and excessive pressure on the environment (FAO 2007). In the past 20 years, many indices have been developed to quantitatively evaluate water resources' vulnerability (e.g., water scarcity or water stress). The Falkenmark indicator (FI) is perhaps the most widely used measure of water stress. It is defined as the fraction of the total annual runoff available for human use. Many countries have been surveyed and the water usage per person in each economy has been calculated. Based on the per capita usage in Table 1, the water conditions in an area can be categorized as: no stress, stress, scarcity, and absolute scarcity (Brown & Matlock 2011).

Table 1

Water barrier differentiation proposed by Falkenmark (1989) 

Index (m3 per capita)Category/condition
>1,700 No stress 
1,000–1,700 Stress 
500–1,000 Scarcity 
<500 Absolute scarcity 
Index (m3 per capita)Category/condition
>1,700 No stress 
1,000–1,700 Stress 
500–1,000 Scarcity 
<500 Absolute scarcity 

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