Quantitative Analysis of Crop Yield Shocks and the Influence of Climate Change

Sudden reduction in crop yield greatly disrupts the food supply in a country. Such shocks amplify food insecurity, affect farmers welfare along with economic benefits, and destabilize global food systems. To understand these negative impacts of yield losses, it is important to quantify the variability in yield. A number of studies have investigated yield variation, but less discriminate between positive and negative deviations from the mean yield. Moreover, the assessment of drivers for yield variation often included climate variation as a key driver, but considered few socioeconomic drivers. Here, we approach these knowledge gaps, by examining the spatio-temporal patterns of negative yield deviations and their drivers. Using wheat yield as an example, we investigated the negative shocks in the yield in 90 major wheat producing countries during 19612014. To model the negative shocks, we developed a range of variables that quantify the extreme weather stress for each country, and included other socioeconomic variables in the model, such as gross domestic product (GDP), percentage area irrigated, and N fertilization. To examine the relationship between negative shocks and the drivers, we modeled the lower quantiles (e.g., 1%, 5%, and 10%) of yield anomalies, which generally represent severe yield losses in a country, using statistical and machine learning techniques of quantile regression. The preliminary results demonstrate the rising frequency and intensity of negative shocks with time, in contrast to the declining trend shown by coefficient of variation (CV). These results highlight the importance of assessing the negative shocks beside CV. Furthermore, quantified the effect for a given combination of factors outside the conditional mean of response variable. The outcome of quantile regression confirmed that a country with higher extreme heat stress tends to face severe negative shocks. However, surprisingly, GDP and N fertilization showed negative association with the shocks, indicating that improving GDP and N fertilization does not necessarily stabilize crop supply. As the extreme weather stress is enhancing in many regions of the world, the severity of negative shocks is expected to continue to rise, indicating a growing challenge for stabilizing the global food supply.