yield time series, fluctuation, stability, variability, risk
Abstract
The long term time series of the yields of various crops in many countries show wide fluctuations around an increasing trend, the main reasons of them may be variability of weather and the continuously changing economic environment.
Technology can be considered suitable for the production, if it agrees with the ecological features of the area, that is, it can compensate for the weather anomalies typical for the region, so that yields do not vary to a great extent. The measurement of yield variations caused by different natural resources and changing weather is not
straightforward, and it is not easy to say what amount of variability can be considered reasonably small for the safe, riskless production, and what is the extend at which risk is unacceptably high.
The application of absolute or relative standard deviations, or variances to measure yield variability do not seem satisfactory for the assessment of yield stability. For this reason the present paper introduces an indicator, which measures the extreme variations around the trend in long term time series. The objective of
the analysis is to assess the main agricultural crops of the world by the yield time series of the last 40 years, and evaluate the impacts of technology on yield stability. An attempt is made to distinguish crops and countries for which production may be considered "well technologised" and those for which there is reason to
expect crucial technological change. Yield time series of 10 countries and 18 crops were collected from the FAO database for the time period of 1961-2000, to demonstrate the advantages of the applied method.
