Sustainable Farming

For the first time, satellite remote sensing of a 2000-kilometer swath running from eastern Pakistan across northern India and into Bangladesh has put a solid number on how quickly the region is depleting its groundwater. The number "is big," says hydrologist James Famiglietti of the University of California, Irvine--big as in 54 cubic kilometers of groundwater lost per year from the world's most intensively irrigated region hosting 600 million people. "I don't think anybody knew how quickly it was being depleted over that large an area."
...
groundwater was being pumped out 70% faster in this decade than the Central Ground Water Board of India estimated it was in the mid-1990s. The apparent surge in withdrawal would have been large enough to turn a once-stable water table into a falling one that demands ever-deeper wells and bigger pumps and may draw in salty or polluted water

- Science Magazine

The world's food production needs to double by 2050 to feed the world's growing population. But over this period, climate change, reduced access to water and changing land use are likely to make growing crops harder rather than easier.

- BBC News

On one hand, we are loosing our water reservoirs - groundwater, snow packs and glaciers, freshwater lakes - rapidly. Water tables are falling almost everywhere in India, due to "Green Revolution" methods that emphasized pumping groundwater:

To date, India’s 100 million farmers have drilled 21 million wells, investing some $12 billion in wells and pumps. In a survey of India’s water situation, Fred Pearce reported in the New Scientist that “half of India’s traditional hand-dug wells and millions of shallower tube wells have already dried up, bringing a spate of suicides among those who rely on them. Electricity blackouts are reaching epidemic proportions in states where half of the electricity is used to pump water from depths of up to a kilometer.”

In Tamil Nadu, a state with more than 62 million people in southern India, wells are going dry almost everywhere. According to Kuppannan Palanisami of Tamil Nadu Agricultural University, falling water tables have dried up 95 percent of the wells owned by small farmers, reducing the irrigated area in the state by half over the last decade. As a result, many farmers have returned to dryland farming. [ref]

Even a small increase in temperatures ... could push down crop yields in southern regions of the world... A greater frequency of droughts and floods, the agency added, could be particularly bad for agriculture.

"Rain-fed agriculture in marginal areas in semi-arid and subhumid regions is mostly at risk," Diouf said on a visit to the southern Indian city of Chennai. "India could lose 125 million tons of its rain-fed cereal production, equivalent to 18 percent of its total production."

• build ever larger dams and canal networks [ref],
• exploit deep water aquifers,
• build expensive water desalination plants [ref], and
  
• commodify water [ref, ref]

• promote universal small scale water harvesting, especially on drylands [see previous post] and
• phase out annual crops that are completely dependent on rains in favor of perennials and tree crops that can withstand inconsistent and unpredictable weather patterns.