Globally, about 24% of the water used for food production is traded . Because about 10% of precipitation over land masses or 16% of terrestrial evapotranspiration is used by agro-ecosystems , virtual water trade accounts for about 2.4% of precipitation over land and 3.8% of terrestrial evapotranspiration, a nontrivial amount of water. Recent studies have shown that virtual water trade accounts for 11% of the global depletion of groundwater. In other words, 11% of the nonrenewable use of groundwater resources worldwide is due to exports, particularly from Pakistan, India, and the United States . Overall, food security strongly depends on virtual water transfers . Through the intensification of trade, some regions have become strongly dependent on food produced with water resources they do not control because they are located elsewhere . Such a globalization of water resources has been escalating since the 1980s , and its implications on food and water security have just recently started to be appreciated .Recent work has stressed the pros and cons of trade. Through virtual water trade, local food demand can be met even in water-scarce regions without engendering famine, conflict,hydroponic bucket or mass migration ; this often occurs at the expense of societal resilience and environmental stewardship while generating environmental externalities .

The possible implications of the globalization of water for food and energy security remain overall poorly understood, and it is unclear whether trade will generally act as a buffer against, or an intensifier of, vulnerability for nations relying on food imports. On one hand, trade can allow countries to maintain populations greater than would be supported by local natural resources and can act as a stabilizer when local production conditions are variable. On the other hand, this can leave importing countries more exposed to economic and/or environmental shocks that occur beyond their borders and beyond their direct control . In some developing countries, imports of underpriced or subsidized agricultural products may threaten local subsistence farmers and disrupt their systems of agricultural production and livelihoods, with the effect of increasing trade dependency . In the wake of the 2007/2008 global food crisis, it became clear that trade-dependent resource-scarce countries in particular continue to have a limited capacity for absorbing shocks to the food system . At the same time, it has been shown that trade may partly reduce inequalities and injustice in the access to water for food production.Trade across all spatial scales provides a mechanism by which actual and/or virtual resources are redistributed, thus changing inequality patterns with regard to any given resource. Note that, as resource and population distributions vary across spatial scales, inequality also occurs across local, sub-national, and international scales. Geographic conditions and climate dictate the natural distribution and local access to water resources, with potential a virtual transfer and redistribution of those water resources via trade of industrial and agricultural products . This unequal distribution and redistribution of resources is not necessarily unjust, and while trade and/or human migration affects inequality in the distribution of water resources , unless they affect the fulfillment of human rights, they may not necessarily impact injustice .

However, the distribution and redistribution of livelihood is dependent on natural resources and populations and thus inherently contains ethical considerations. The UN acknowledges that water for domestic use and agriculture is a human right . This human right to water can be related to the distribution and redistribution of water resources and populations, thus providing some framework by which to assess justice or injustice in water use for food, at least at a national scale . Within a nation, inequalities are related to poverty, conflict, and sub-national distribution networks . Even cultural food preference and lifestyle can play a role . Thus, water use for food is linked to human dietary requirements and sources of staple food commodities , which typically are impacted by social, cultural, and political influences . Various metrics are available to measure inequality, such as entropy and indicators of variability , but the Gini coefficient is commonly used . The Gini coefficient ranges between 0 and 1 and measures the extent to which the current distribution of resources differs from an egalitarian distribution . Inequality in water use for food production alone has increased over time; however, subsequent trade of food products overall acts to reduce inequality . Carr et al. note that roughly three quarters of the virtual water flows are among water-rich nations and do not reduce inequality. Interestingly, some nations trade in such a manner that it increases inequality and reduces per capita water use relative to well being and malnourishment thresholds . Although the impact of individual trade links on inequality can be determined , other changes, such as reductions in food waste or shifts to more water efficient sources of dietary proteins , can play a large role in ameliorating the impact of inequalities in water use for food.Many drivers controlling the flow of virtual water have been explored, from GDP and rainfall on arable land to geographical distances.

By exploring the impact of multiple factors, such as embedded water, population, GDP, geographical distance, arable land, and dietary demand, the main drivers of virtual water flow appear to be GDP, population, and geographical distance with anonnegligible effect of exporter production . Subsequent work has leveraged this information to explore both link and flux predictions, population, geographical distance, and GDP strongly controlling link activation and the fluxes along those links . Econometric analyses have been used to investigate the extent to which water is a source of comparative advantage , in addition to the classic factors typically considered by international trade theories. Virtual water was found to be a moderate source of comparative advantage with water-rich countries exporting more water-intensive products .Whether the planet Earth will be able to feed the growing human population has been the focus of an ongoing debate lasting more than 200 years . Water availability is expected to become increasingly crucial to food security and human welfare under the increasing demographic pressure . Projections of population growth coupled with predictions of water availability and agricultural productivity have highlighted the manner in which humankind might run out of water for food production in the next few decades under a variety of climate change and land use scenarios . Thus, new strategies are urgently needed to avoid new severe global water and food crises . Current demographic theories rarely consider the scarcity of resources, such as water, as a limiting factor for population growth . However, in some regions of the world the local limits to growth have already been exceeded . Several countries already consume more food than allowed by locally available freshwater resources. This is possible because the water-poor countries rely on the import of food and virtual water from other nations. Thus, the limits to population growth depend on the local water resources and virtual water/food trade. The temporal dynamics of population, local carrying capacity, and post trade carrying capacity can be used to investigate country-specific changes in trade dependency, self-sufficiency, and the extent to which local self-insufficiencies can be successfully addressed by trade . Future projections of the increasing demand for water resources under climate change and population growth scenarios require a better understanding of how food production, human diets, and international virtual water trade are expected to change in the decades to come. Recent studies have provided some preliminary insights into future trajectories of water demand and international virtual water trade . For countries importing food, trade has the effect of increasing the carrying capacity . In this case,stackable planters the long-term trajectory of population growth needs to account for such an increase in carrying capacity, as shown by Suweis et al. with a simple logistic model of population dynamics . In other words, the populations of importing countries are relying on virtual water imports for their long-term trajectory of demographic growth . The opposite is not true, however, for countries exporting food. In fact, there is no evidence of their carrying capacity being reduced because of trade . An analysis based on demographic, crop production, and trade data has shown that in exporting countries the long-term trajectory of population growth tends to converge to a carrying capacity calculated on the basis of local water resources without accounting for the fact that part of those resources are presently contributing to virtual water exports.

This finding means that importers and exporters are counting for their long-term growth on the same pool of virtual water resources . This unbalanced situation could eventually lead to export reduction, which will likely impede the import-dependent countries from meeting their water demands. Some major exporting countries have already reduced their exports in response to spiking food prices during the food crises of 2007–2008 and 2011 . These results highlight a global water unbalance and point out the long-term unsustainability of global food and virtual water trade. Unless new freshwater resources become available or investments in a more water efficient agriculture are made, trade-dependent populations will experience major water stress conditions .The implications for food security are important, particularly if the land was previously used for agriculture by the local populations. In fact, with some exceptions, the crops produced on the acquired land are typically exported and sold on the global market . It has been estimated that the food crops that land investors plan to cultivate on the acquired land could feed about 300–550 million people, which corresponds to about 30–50% of the undernourished global population . These numbers are concerning because most countries targeted by land investors are affected by undernourishment. This phenomenon establishes long-distance teleconnections and inter dependencies between crop production areas and global demand . On the receiving end, the globalization of food markets and the vulnerability and exposure to food crises and climatic shocks make transnational investments in agricultural land a strategic food security priority in order to gain resilience through diversification of the agricultural regions that importer and investor countries rely on. Interestingly, most target countries are endowed with productive agricultural land that in some regions require relatively small amounts of irrigation water and are not affected by aridification under climate change scenarios . As small-scale farming is the most prominent system of food production globally, LSLAs and expansion of commercial agricultural models are producing a global agrarian transformation that has radical societal implications in the target regions. As noted in section 11.1, there is evidence that most of the world’s rural populations depend directly on natural resources and local land for self-subsistence , 2009; Wily, 2011. Moreover, the major share of land small-scale farmers rely on is governed by traditional, customary, and indigenous systems of common property. In sub-Saharan Africa, for example, it has been calculated that 70% of this land can be categorized as customary common property .Transnational LSLAs impact the property access and use of land by traditional users with evidence that traditional systems of common property are most affected . The societal implications of this agrarian transformation include a variety of critical problems , such as dispossession of traditional users and systems of production , evictions and forced migrations , ethical concerns related to violations of human and land tenure rights with particularly negative impacts on women , rise in social conflicts and dynamics of coercion , and multidimensional impacts on rural livelihoods in developing countries .Through LSLAs, land can be put under productive use to the benefit of investors and local communities, arguably , because of “trickle down” effects on employment, and access to modern technology and markets . An often overlooked impact, however, is the land degradation and land use change associated with large-scale land investors . In fact, forests and savannas may be cleared to accommodate new mines or farmlands . Several studies have found that in Indonesia and Cambodia LSLAs are a preferential mechanism for deforestation, with rates of forest loss exceeding those in similar adjacent areas outside land concessions . In other regions of the world, the effect of land acquisitions on forest loss can be indirect. For instance, for Brazil, Hermele reports that acquired land often replaces pastures with cropland, with herders and ranchers then encroaching on forested areas to find new grounds for livestock grazing.The recent escalation in international investments in land has substantial hydrological implications .