Estimating variability of growing season and drought occurrence for rainfed lowland rice area by simulation model

บทคัดย่อ

A simulation model was used for estimating the start and end of growing period using rainfall data from 8 meteorological stations in the Northeast during 1951-2014. Three groups of rainfall based on mean across 64 years were separated to be high (1556 mm.), intermediate (1397 mm.) and low (1161 mm.) rainfall groups. To determine the difference in rainfall, start and end of growing periods (SGP and EGP) and opportunity of drought occurrence, the rainfall data were grouped into 5 periods, 1951-1979, 1980-1989, 1990-1999, 2000-2009 and 2010-2014 in comparison to means of 64 years. Amount of rainfall among the periods was not different, excepted 2000-2009 which was slightly increased. Start and end of growing period were determined at 80 percentage probability. Mean of SGP was not different between the high and intermediate rainfall groups (late May) but it was late under low rainfall group to mid-June to late July. Among the periods of years, there was no difference but it trended to be earlier for the last 5 years period. Mean of EGP across 64 years was earlier for the lower than higher rainfall groups. Among the periods, there was no difference, excepted during 2010-2014 which trended to be slightly delayed. Possibility of early season drought (ESD) was higher in low than high and intermediate rainfall groups. However, there was the increase during the last period in comparison to mean of 64 years for intermediate rainfall group. Late season drought (LSD) occurrence was the same as ESD which higher in lower than higher rainfall groups. The result suggested that there was not much change in SGP and EGP. However, there was increase in possibility of ESD under low and intermediate rainfall groups. In order to minimize risk to the change, planting date and rice varieties need to be considered.