When water availability is so low to be life threatening, yield will be very low even if plants survive.
The ongoing drought in Californian has also threatened yields.
Much of northern China is in the grips of a months-long drought that could threaten yields of wheat and other crops this spring.
The pattern typically brings below average rainfall for the Asia Pacific region, threatening the yields of agricultural crops, while America is often hit by wetter than average weather.
The threatened return of budget deficits as the Bush administration and Congress prepare $100 billion in stimulus packages lifted longer-term yields.
These environmental changes are already threatening crop yield but their long-term impact on ecosystems and food productivity remains unclear.
They include millions of smallholder farmers who are bearing the brunt of today's major global changes: widening economic inequality, relentless degradation of the ecosystems on which food production depends, and the quickening pace of climate change, which threatens crop yields worldwide.
Sustainable disease management must be developed for plant pathogens that could threaten maximized yields.
And because it washes away rich topsoil, erosion can threaten crop yields.
A Syngenta spokesman told the Guardian's Damian Carrington that without the use of neonicotinoids, pests (in particular flea beetles) threaten crop yields.
