A Quantitative Approach to Associate Crop Production and Precipitation

Enhancing realization of precipitation impacts on agricultural crop production requires an appropriate method, which can explain precipitation distribution. In this study Uniformity Indices based on the distance between cumulative precipitation curves and the respective theoretical Uniformity precipitation lines, which join the lowest and highest cumulative precipitation values within the considered time period, were calculated and applied as a method to explain precipitation distribution. In addition, the concentration index (CI) that evaluates the varying weight of daily precipitation, i.e. the contribution of the days of greatest precipitation to the total amount, was calculated as well for comparison. The relationship between the derivative indices and yield of two major crops (wheat and barley) were also evaluated over a 30-years period (1984-2013), under two different climate conditions (Semi-Arid and Mediterranean) in two different regions. Both methods were applied for the whole crop growth season, planting to harvest, and two critical crop development stages, germination and reproductive growth. Both crops yield showed significant association with ER (the slope of the Uniformity line) (up to 0.75), but not to UR (The index of the non-Uniformity of precipitation distribution). Significant correlations were also found by calculating the indices over short-term periods during reproductive stage of crops growth (up to 0.64), which indicates that how these indices can be more effective when appropriate development periods for different crops were considered. The CI index was not able to realize the semi-arid and Mediterranean conditions compared with uniformity index.