Biology subjects

Mehrabi, Z.

Publications and source records attributed to Mehrabi, Z..

3 recordsLinked to original sources

bioRxiv2018

On the synchronized failure of global crop production

Multiple breadbasket failure is a risk to global food security. However, there are no global analyses that have assessed if global food production has actually tended towards synchronized failure historically. We show that synchronization in production for major commodities such as maize and soy has declined in recent decades, but that increased synchrony, when present, has had marked destabilizing effects. Under the hypothetical case of a synchronized failure event, we estimate simultaneous global production losses for rice, wheat, soy and maize between -18% and -36%. Our results show that maintaining asynchrony in the food system and mitigating instability through food storage in good years, both require a central place in discussions of future food demand under mean climate change, population growth and consumption trends.

ecology↗

bioRxiv2017

The cost of heat waves and droughts for global crop production

Heat waves and droughts are a key risk to global crop production and quantifying the extent of this risk is essential for insurance assessment and disaster risk reduction. Here we estimate the cumulative production losses of six major commodity groups under both extreme heat and drought events, across 131 countries, over the time period of 1961-2014. Our results show substantial variation in national disaster risks that have hitherto gone unrecognised in regional and global average estimates. The most severe losses are represented by cereal losses in Angola (4.1%), Botswana (5.7%), USA (4.4%) and Australia (4.4%), oilcrop losses in Paraguay (5.5%), pulse losses in Angola (4.7%) and Nigeria (4.8%), and root and tuber losses in Thailand (3.2%). In monetary terms we estimate the global production loss over this period to be $237 billion US Dollars (2004-2006 baseline). The nations that incurred the largest financial hits were the USA ($116 billion), the former Soviet Union ($37 billion), India ($28 billion), China ($10.7 billion) and Australia ($8.5 billion USD). Our analysis closes an important gap in our understanding of the impacts of extreme weather events on global crop production and provides the basis for country relevant disaster risk reduction.

ecology↗

bioRxiv2017

Does no-till agriculture limit crop yields?

No-till is an agricultural practice widely promoted by governments, development agencies, and agricultural organisations worldwide. However, the costs and benefits to farmers adopting no-till are hotly debated 1-4. Using a meta-analysis of unprecedented study size, Pittelkow et al.5 reported that adopting no-till results in average yield losses of -5.7%, but that these losses can be limited with the added implementation of two additional conservation agriculture practices - crop rotation and crop residue retention, and in dry environments. They claimed that, as a result, resource limited smallholder farmers, that are unable to implement the whole suite of conservation agriculture practices are likely to experience yield losses under no-till. In a re-evaluation of their analysis, we found that they overly biased their results toward showing that no-till negatively impacts yields, and overlooked the practical significance of their findings. Strikingly, we find that all of the variables they used in their analysis (e.g. crop residue management, rotation, site aridity and study duration) are not much better than random for explaining the effect of no-till on crop yields. Our results suggest that their meta-analysis cannot be used as the basis for evidence-based decision-making in the agricultural community.

ecology↗