Effect of AGW on wheat

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Re: Effect of AGW on wheat

Postby HBS Guy » 19 Jul 2017, 19:31

The effect of AGW on wheat crops

Wheat, with about a 2.1 million km2 total harvested area, is the most abundant crop in the world: it is the first rain-fed crop after maize and the second irrigated crop after rice (Portmann et al 2010). With a total production that surpassed 700 million tons (MTons) in year 2010, it is contributing to about the 20% of the total dietary calories and proteins worldwide (Lobell and Gourdji 2012, Shiferaw et al 2013).

So wheat is kinda important—and it is in trouble from AGW!

Field studies . . . have shown that higher than optimal temperatures during the growing season are generally accelerating the progress of the plant phenological stages, affecting photosynthesis and its balance with respiration, and reducing the final yield (Lobell and Gourdji 2012, Rezaei et al 2015). Higher temperatures also increase the atmospheric demand for water and reduce the crop water-use efficiency (Ray et al 2002). Exposure to extremely high temperatures (i.e. heat stress) leads to plant damages by inducing perturbations in cellular structures and metabolic processes (Nakamoto and Hiyama 1999). Isolated occurrences of extreme high temperatures around a sensitive stage of crop development, such as flowering and grain-filling, can reduce grain yield considerably (Tashiro and Wardlaw 1990, Ferris et al 1998, Porter and Gawith 1999, Luo 2011), while a prolonged period of extreme high temperatures might result in almost total yield loss (Semenov and Shewry 2011).

Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate. . . .phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle. Examples include the date of emergence of leaves and flowers. . .

While irrigation may provide some cooling in extreme temperatures by evaporation,
On the other hand, extreme amounts of precipitation and water excess in the soil can also be responsible for wheat loss due to proliferation of pests and diseases, leakage of nutrients, inhibition of oxygen uptake by roots, and interference with agronomical practices (e.g waterlogging during harvest). . . .

Compared to other important crops, the main wheat producing regions are characterized by 'close-to-average' yield variability (Ben-Ari and Makowski 2014). However, increasing unfavorable conditions under observed and projected climate change conditions will probably impact wheat production variability (Gourdji et al 2013, Deryng et al 2014, Siebert and Ewert 2014, Asseng et al 2015, Ray et al 2015), especially because of the exacerbated effects of heat stress on grain number and grain size (Lobell et al 2015).

This years winter wheat harvest in Kansas and surrounding states was hurt by the warm winter causing the plants to grow and develop much faster than normal in the winter months. When a late spring blizzard hit the wheat fields a lot of the plants were killed off. Are these warm US winters a new trend—if so winter wheat will have to be planted later.

. . .considering that the human population increased proportionally from 4.4 billion in 1980 to 6.9 billion in 2010 (UN 2015), negative yield deviations from the mean trend can be a potentially increasingly threat to food security. Indeed, changes in wheat yield variability have already been suggested as one of the primary factors influencing global food prices, market stability and food security, especially in developing countries (FAO 2011, OXFAM 2012, Porter et al 2014, Deryng et al 2014, GFS 2015). Moreover, the current urbanization trend at the expense of cropland area extent would imply, to be sustainable, a further increase of crop yield (Bren d'Amour et al 2016), and presumably an increased sensitivity of food security to the climate induced yield interannual variability.

More people, less cropping land—better that nothing too harmful will come from AGW!

The study concluded:
The combined stress index (CSI), defined as a linear superposition of the Standardized Precipitation Evaporation Index (SPEI, Vicente-Serrano et al 2010) and of the Heat Magnitude Day (HMD, this study), allows explaining the 42% of the variability globally (confirming and strenghtening the result of Ray et al 2015), and often at country level as well. Therefore, accurate yield forecasts in the major producing countries could provide useful insights in global production, potentially increasing food security. In fact, we are currently working on the application of the CSI in a seasonal forecasts context (Ceglar et al submitted).

Our result points to a clear role of climate anomalies and extreme events on wheat yield anomalies and enables identifying the relevant contributors and the associated effects. Heat stress is often the most important predictor, consistently with field studies and future projections, and it is in general as important as drought. As a prominent exception, we have found that in the Mediterranean countries drought carries a larger detrimental effect on wheat yield than heat stress.

Heat stress over wheat cropping regions increased significantly in the period 1980–2010, especially since the mid-1990s. This produced less compensating and more concurrent yield anomalies, motivating the general concern about food security.

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