Computer model for simulation of occurrence of dry spells and decrease of crop yield

Author(s)

Sérgio Antônio Veronez de Sousa

• Document type: Doctoral Thesis
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 1999-05-07
• Advisor: José Antônio Frizzone

Abstract

A computational model was written in '”turbo pascal for Windows” to simulate, using Monte Carlo’s Method, the occurrence of sequences of dry days during the cropping season and the consequent decrease in yield for a given crop. The developed program simulates, starting from a historical series, which the occurrence and the respective period of return of dry spells of different intensities. It also simulates the daily evapotranspiration for a certain month. With the simulate values, can be determined the production decrease for a given culture, due to the deficit of evapotranspiration accumulated. The model allows the choice of three options. The first simulates the occurrence frequencies and the periods of retum of dry spells of different intensities, for a region previously selected. The second, besides the occurrence of the same ones, it allows the determination ofthe effect of these dry spells on a certain culture. The third option allows to calculate the effect of a dry spell, of previously established duration, on the culture yield. The option 3 was used to simulate values of evapotranspiration deficit in the com crop, for the region of piracicaba, for periods of 7, 15 and 3 o days without rain, in the months of march and july, being the simulate deficit values for the normal and triangular functions. The values of evapotranspiration deficit were also calculated, for the as, same periods and months, being used observed values of the evapotranspiration, for three years draftee among the ten years previous to the series used in the simulations, being these values compareci with the simulate ones by the program, for the two functions. The results showed that the average values of simulated evapotranspiration déficit by normal and triangular functions differed statistically by tukey test at the 5% of probability level. The simulated evapotranspiration deficits by normal and triangular functions showed small differences, with averages less than 10% on march and 5% on july. The values ofthe evapotranspiration deficit, simulated by two functions, presented a good adjustment when compared to the observed values, for the same conditions, in the three appraised years, presenting high adjustment indexes and correlation coefficients. The normal function provided a better adjustment, when compared with the triangular function, for a same month. For a same function, the values simulated for the month of march provided a better adjustment, in relation to the simulated for july. ln another evaluation the program was used to make maps of frequencies of occurrence of dry spells of different durations for the São Paulo state. were used 25 years of precipitation data obtained in 91 pluviometrics stations of the state. The maps were made using geostatistics techniques and they allowed to identify the frequencies of occurrence of dry spells of different durations in any places of the São Paulo state. The developed model can be used to calculate the best cultivations times, working as an important tool in the planning of the agriculture, besides supplying subsidies for the study of the viability of implementation of irrigation systems. (Attachments only available in print verson) (AU)