عنوان مقاله [English]
نویسندگان [English]چکیده [English]
The water crisis has become a serious issue in Iran in recent years due to the arid and semi-arid nature of the country. The water issued in the production processes is called "Virtual Water", some of it remains in the product. When these products enter the international markets, virtual water trade happens. Virtual water trade is expected to decrease water use in national and international levels due to the efficient and specialized use of water. Nowadays, the concept of virtual water is an important issue in water resource management.
In this paper, the volume of virtual water trade was investigated for six main crops of Hamedan province in four groups: cereal (wheat and barley), vegetables (potato and garlic), industrial (sugar beet), and provender (alfalfa) over the period 2001-2010.
The components of crop VWC are the type of water resources used in the crop growth process, including blue water (surface water or groundwater) and green water (effective precipitation). Under a rain-fed scenario, green water is equal to the total VWC of the crop. The VWC of primary crops can be calculated according to the methodology developed as follows:
where c، i، j are crops number, city and year, respectively indicates average water requirement (m3/ha), Ac,i,j is Area (ha), TAc,j is Total area (ha), VWCc,j is virtual water (m3/ton), and indicates average yield (ton/ha).
The water requirement of crops was calculated by Hargereaves-Samani method and daily meteorology data of Hamedan station (equation 2):
where Ra is solar radiation (Mj/m2/day), Tmean is the average air temperature (oC), and Td is Tmax-Tmin (oC).
The results showed that the virtual water volume of industrial and vegetables group is lower than 1 kg/m3 and not water-intensive crop with high water use efficiency. Meanwhile, cereal groups with virtual water volume greater than 2 m3/kg are water-intensive crops with low water use efficiency. Furthermore, during 2001-2010, the difference between virtual water exports and imports demonstrated that 1538.4 MCM net water is harvested from water resources of Hamedan province.
Table 1- The required parameters for calculating VWC, Total net virtual water trade (TNVW), CWP, Water use intensity (WI), Water dependency (WD), Water self-sufficiency (WSS) of six crops during 2001-2010
WSS WD WI WA WU CWP TNVW VWI VWE VWC Parameter
100 0.0 17.7 3091 546.1 1.2 -65.9 0.0 65.9 0.8 11.2 9066 Alfalfa
100 0.0 16.4 3091 507.6 0.4 -132.8 0.0 132.8 2.5 2.7 634 Barley
100 0.0 32.5 3091 1004.7 0.2 -1146.2 213.7 1359.9 4.5 1.7 7169 Wheat
100 0.0 0.5 3091 14.3 3.5 -4 0.0 4 0.4 15.8 4561 Garlic
100 0.0 8.6 3091 266.4 3.6 -167.5 0.0 167.5 0.3 32.1 8889 Potato
100 0.0 2.3 3091 72.4 3.6 -21.9 0.0 21.9 0.3 31.1 8741 Sugar beet
100 0.0 13.0 3091 401.9 2.1 -256.4 35.6 292 1.5 15.8 7461 Mean
According to Table 1, the minimum amount of water requirement belongs to garlic crop with 4560.8 m3/ha and maximum amount of requirement water is equal 9066.3 m3/ha in alfalfa crop. The important point in Table 1 is less the amount of virtual water on alfalfa, potato and sugar beet crops with high water demand, in contrast barley and wheat crops with less water requirement.
With consideration of irrigation efficiency about 60%, the actual amount of water harvesting from Hamedan water resources is 2564 MCM. The economic value of virtual water calculations showed that Hamedan province is exported an average of 19547 Rials water out of the province during the years 2001- 2010. Therefore, it is necessary to apply suitable policy to prevent large amounts of water exports. By considering the results of this study, it seems that the increasing trend of agriculture crop exports, especially those with high water requirements in the recent years facing with drought event isn’t compatible with water resource contents.
Therefore, reducing the area under cultivation and lower exports of agricultural products, lead to storage of water resources in the province. However, a more appropriate solution is increasing of crop yield. Due to the negative balance of water in the aquifers of the province, it could be based on studies of virtual water, and economic valuation of water, with imported products with high virtual water content, and export products with low levels of virtual water, water use efficiency will be increased. Therefore, for optimal use of water, it should be combined policy of export and import of agricultural products, taking into account the economic benefits.