As society reaches the limits of available farmland and accessible irrigation water, many countries have turned to international markets to help meet domestic food demand. Imports of grain worldwide have increased more than fivefold between 1960 and 2013. However, importing food as a response to resource scarcity creates dependence on global markets, writes Gary Gardner, director of publications at the Worldwatch Institute, in the Institute's latest Vital Signs Online article (www.worldwatch.org).

"In 2013, more than a third of the world's nations---77 in all---imported at least a quarter of the major grains they needed. This compares to just 49 countries in 1961," writes Gardner. "Meanwhile, the number of grain-exporting countries expanded by just 6 between 1961 and 2013."

Food import dependence has several roots. One problem is the steady loss of fertile land and fresh water. In 62 countries, the area of farmland is insufficient to meet domestic consumption needs, and in 22 countries, the consumption of agricultural products (not just grains) requires more fresh water than each country can extract.

Despite the importance of farmland, land continues to be degraded or paved over. Farmland near cities is regularly converted to accommodate housing, industry, and other urban needs. The United States, for example, lost 9.3 million hectares of agricultural land to development--- an area the size of the state of Indiana---between 1982 and 2007.

Pressure on water supplies for agriculture is also becoming widespread. A 2012 study in the journal Nature estimated that some 20 percent of the world's aquifers are pumped faster than they are recharged by rainfall, often in key food-producing areas.

Another threat to national endowments of farmland has emerged in the practice of "land grabbing"--- the purchase or leasing of land overseas by investment firms, biofuel producers, large-scale farming operations, and governments. Since 2000, agreements have been concluded for foreign entities to purchase or lease more than 42 million hectares, an area about the size of Japan. The bulk of the grabbed land is located in Africa, with Asia being the next most common region for acquisitions.

"The largest source of land grabbing is the United States, where investors see an opportunity to make money on an increasingly limited resource," writes Gardner. However, "contracts often do not take into account the interests of smallholders, who may have been working the acquired land over a long period."

Importing food as a response to resource scarcity has two clear dangers. First, not all countries can be net food importers; at some point the demand for imported food could exceed the capacity to supply it. Already, many major supplier regions are themselves experiencing resource constraints. Second, excessive dependence on imports leaves a country vulnerable to supply interruptions, whether for natural reasons (such as drought or pest infestation in supplier countries) or political manipulation.

An import strategy may be unavoidable for some nations, but it should be considered only reluctantly by countries that can meet their food needs in more conventional ways. It is crucial to conserve agricultural resources wherever possible.