Relationships between weather variability, agricultural production variablilty and food security.

摘要

Global food security is impacted by aggregate agricultural production variability at the global level. The United States produces and exports a substantial amount of crop commodities. So, a production shortfall in the U.S. results in some price spike as well as quantity shortfall at the global level. This study examined production variability of corn in the U.S. since 1970 and found that relative production variability after factoring in the trend effect had declined over time. In the U.S. and world, weather has been a primary factor causing occasional production shortfall of major crops. To better understand the impact of weather on corn yield a new index, Net Crop Moisture Deficit (NCMD), was created. NCMD captures the marginal contribution of an inch of water on yield at different spatial and temporal scales taking into consideration plant biological requirements. NCMD was compared with more widely used seasonal aggregate precipitation data for fourteen sample Nebraska counties and was found to do a superior job of identifying both drought and non- drought years. Moreover, it was also found that NCMD values through July predicted expected deviation from yield quite well. This study also empirically analyzed and found that the recently popular Drought Mitigation Center (DMC) data was linked satisfactorily to corn yield. When the DMC measure was compared with NCMD it was found that NCMD was marginally superior to DMC data in identifying drought and no-drought years as well as making predictions for expected deviation of yield for corn. After identifying the years when production shortfall was a result of yield and/or acreage decrease in the U.S for three major crops (corn, soybeans, and wheat), examination of changes in utilization categories and effect on world price indices was done. The analysis revealed that stocks and exports accounted for the majority of the adjustments during production shortfall years. However, the rebound time or time required to reach the expected production level as well as utilization level for all major categories, after production shortfall was only one or two years, suggesting the normal market forces rather quickly restore production and prices of major crop commodities. The world price indices saw some increase due to the U.S. production shortfall but for the most part also fell back to the shortfall previous year level within one to three years. This implied that global food security problem in the short run is generally manageable given appropriate levels of stocks maintained at national and global levels.