Implications of seasonal rainfall trends for agriculture in the dry zone of Sri Lanka

Abstract

Sri Lanka is vulnerable to the changing climate because of the departures from the usual rainfall. This paper analyses the consistency in trends of rainfall in the dry zone of Sri Lanka with particular emphasis on the influence of four monsoon seasons on the regional agriculture. The data analyzed consists of the daily rainfall records (1996-2015) at 10 stations distributed throughout the dry zone of Sri Lanka. The non-parametric Mann-Kendall and Sen-Theil statistical methods were used for the investigation which is appropriate for the non-normal data with missing or censored records. To analyse the data with seasons, modified seasonal Mann-Kendall trend test was used. The pre-whitening method was applied to remove autocorrelation from the time series. Though the results show an increasing annual rainfall, a consistent reduction has been revealed in monthly rainfall during June and July. Nearly 30% of the stations demonstrated a statistically significant (p<0.05) increase in rainfall during the northeast monsoon season. However, statistically significant decline in monthly rainfall during June and July led the dry zone drier, which may have reduced the availability of the irrigable surface water during Yala (minor rainy) season. Findings of rainfall variation in dry zone help speculate water availability for crop requirement in the dry zone in Sri Lanka.