Impacts of rainfall variability on paddy production: A case from Bayawa minor irrigation tank in Sri Lanka

摘要

Rainfall (RF) variability has been suggested as the primary reason for low paddy production in the recent past under minor irrigation tanks (MITs). A study was conducted to verify the relationship between observed crop success/failures and the RF variability in the Bayawa MIT system in the Kurunegala district of Sri Lanka. Seasonal and annual RF variability and its effect on paddy crops were analyzed. Daily rainfall data were obtained from the Wariyapola station from 1983 to 2014. Paddy production data for 20 consecutive seasons from 2003 to 2014 were collected from the Department of Census and Statistics (DCS), Colombo. Paddy samples from the Bayawa command area were used to calculate the land productivity and compared between the two cultivation seasons. Three types of direct RF impacts on paddy production in the Bayawa MIT system were identified: (1) reductions in the cropping intensity (CI), (2) total crop failures and (3) reductions in yield. During the study period, the CI was 80-173% with an average of 140% (expected value is 200%). Sixty percent of annual and seasonal RF values were below the long-term average showing a direct effect of RF on crop failures. Low production is not only due to the variability of annual or seasonal RF during the cultivation seasons, but also due to poor water management decisions, such as not cultivating considering the available water in the MIT. Thus, there is a need for wise water management decisions of MITs in this study area based on the variability of RF for sustainable paddy production.