by Coco Coyle
Increases in numbers and intensity of extreme weather disasters are linked to climate change and rising global temperatures. Agriculture is both a cause and a victim of climate change, and is susceptible to natural disasters and extreme weather disasters (EWDs). Lesk et al (2015) estimate global cereal production losses resulting from four major types of EWDs—extreme heat, droughts, extreme cold, and floods—in the period 1964–2007, analyze the underlying processes resulting in those losses, and identify several areas with potential for further study. They found that extreme heat disasters and droughts on average reduced national cereal production by 9–10%, while there was no significant drop in production from extreme cold and floods.
The study used a statistical analysis method known as superposed epoch analysis, which is designed to isolate the effects from the desired variable (in this case, effects from EWDs only). Lest et al used data for the time period 1964–2007 provided by the Emergency Events Database, as well as disaster reports from United Nations agencies, national governments, and the International Federation of Red Cross and Red Crescent Societies. In order to determine production losses, this study considered both total harvested area and yield, or % of maximum possible cereal grown in a particular harvested area, and included 16 types of cereal crops. Including both figures also provides a basis for analysis of the processes leading to production losses. The reported figures estimate average cereal production losses per nation, per disaster.
Using these methods, Lesk et al found a 9.1% loss of cereal production from extreme heat, 10.1% loss from droughts, and no significant losses from either extreme cold or floods. This may be because floods tend to occur in warmer regions in the springtime, and are relatively short disasters or occur before the growing season begins. Similarly, extreme cold disasters often occur in winter, outside the growing season, therefore not affecting the growth of crops. By contrast, droughts are longer-lasting disasters, affecting many years’ worth of crops, and extreme heat disasters typically occur during the summer months, at the height of the growing season, damaging more crops without time for replanting. Another possible explanation is that floods and extreme cold tend to be more localized, effecting smaller land areas than droughts and extreme heat.
The study also found evidence that droughts are increasing in intensity. A~7% greater production loss from more recent droughts (1985–2007) was found compared to the earlier years studied (1964–1985): cereal production losses in the later period averaged 13.7% while earlier droughts caused an estimated 6.7% production losses.
Additionally, the study found that developed nations are more at risk from EWDs than undeveloped nations. Several factors make developed nations more vulnerable. First, they tend to have higher instances of crop monocultures and larger average farm size, whereas undeveloped nations tend to have smaller farms with a diversity of crops providing an overall more durable agricultural system. Secondly, smaller-scale operations tend to use more risk-management strategies than large-scale ones. Finally, undeveloped nations may simply have lower yields prior to experiencing EWDs.
This kind of data collection and analysis may prove extremely important in future disaster preparation and in studying the effects of climate change on agriculture. Data analysis like that done by Lesk et al—as well as more specific analysis performed on a single region or investigating one type of disaster—could assist policymakers develop more effective disaster adaptation programs or risk management in agriculture.
Lesk, C., Rowhani, P., Ramankutty, N., 2016. Influence of extreme weather disasters on global crop production. Nature 529, 84–87.