THE EFFECTS OF USE OF AVERAGE INSTEAD OF DAILY WEATHER DATA IN CROP GROWTH SIMULATION-MODELS

Development and use of crop growth simulation models has increased in the last decades. Most crop growth models require daily weather data a s input values. These data are not easy to obtain and therefore in man y studies daily data are generated, or average values are used as inpu t data for these models. In crop growth models non-linear relations of ten occur. Thus the simulation result with average data can be differe nt from the average result with daily data. In this study the effects of using average weather data on simulated potential and water-limited yields were investigated with a spring wheat crop growth model. It wa s expected that deviation in simulation results was related to the var iability of the weather. Therefore effects were studied for sites in t hree different climates: temperate maritime, mediterranean and humid t ropical. Variability of the weather during the growing season on these sites was quantified. Intuitively the weather in the mediterranean an d humid tropical climates is far more constant than the weather in the temperate maritime climates. However, for all locations the variabili ty of the weather during the growing season was nearly the same. The e xplanation for this unexpected result was found in the fact that on al l sites crops were grown in that part of the year in which it rains. T he existence of dry and wet days during the growing season causes a la rge day-to-day variation in weather. For all sites an overestimation o f the simulated potential yield of 5-15% was found as a result of usin g average weather data. For water-limited production the use of averag e data resulted in overestimation of yield in the wet conditions and u nderestimation of yield in dry conditions (up to 50%).