Identification of the potential of growing seasons by the onset of seasonal rains: A study in the DL1 region of the north central dry zone

Abstract

Although rainfall in the Dry Zone of Sri Lanka is highly variable spatially and temporally, years with favourable rainfall distribution could occur and it is necessary to strive for agricultural product maximizing strategies in such years. Recent studies have shown that there is a possibility of predicting the potential of the rainy seasons ahead using the correlation structure of the onset of rains and subsequent seasonal characteristics. Nevertheless, non-availability of long sequences of data limit the appropriateness of parameters of such stochastic models due to the relatively low number of extreme events found in a short data series. Under these circumstances, stochastic simulation of long sequences of rainfall data provide a better estimate of the frequency of infrequent notable events simply by providing an increased number of such events in long sequences of simulated rainfall records. Hence, a study was undertaken to find the relationship between onset time of the seasonal rains in DL, agro-ecological regions and subsequent seasonal characteristics such as withdrawal of rains, length of the season and amount of seasonal rainfall. The data used for the study was simulated using a stochastic rainfall generator developed for the Dry Zone's environment. Results revealed that the withdrawal of the Maha rains occurs at the end of January and hence, late onset of the Maha rains in the DL, region reduces the length of the effective Maha season. However, there was no strong evidence to suggest that the onset of the Maha season has an impact on the amount of total rainfall during the Maha season. Irrespective of the onset of the season, Yala rains paused around 5-6 weeks from their onset. However, it was clearly evident that tho onset of the Yala rains cannot be used as a predictor for the amount of seasonal rainfall during the Yala season.