Climatic considerations which support the choice between natural rubber and oil palm in Nakhon Si Thammarat, southern Thailand

Four climatic variables-rainfall, number of rainy days, relative humidity, and temperature-were studied to observe the characteristics and probable occurrences outside the required bounds for the optimal growth of oil palm and natural rubber. These two economic crops have become increasingly popular among farmers in Nakhon Si Thammarat province, southern Thailand. Monthly and annual data during 1981-2011 were analyzed using appropriate time-series techniques. The out-of-bound probabilities were calculated using the counting method. Only the rainfall showed a significant and increasing trend while the trends in the other variables were not significant. All studied variables showed seasonal fluctuation and cyclical movements. No significant irregularities appeared in the data. The probable occurrences of these climatic variables are crucial in determining the regular and sufficient levels of rainfall required for oil palm and natural rubber. Climate risks were less for growing natural rubber. This study concluded that natural rubber was a more climatically suitable crop for Nakhon Si Thammarat province, if only the four stated climatic variables were considered.