Abstract:
The effect o f rainfall on cropping pattern among farm ers in the Hambantota district was studied by analyzing the spatial and temporal variation o f rainfall, with respect to rainfall magnitude, risk and onset. The rainfall data over 42 years (1960-2002) in six rain gauge stations andpan evaporation data atAngunakolapelessa meteorological station in Hambantota district were used for the analysis. Yearly and monthly magnitudes o f rainfall were expressed by mean annual rainfall, annual dependable rainfall and monthly mean rainfall respectively. Hargreaves Moisture Availability Index at 75% probability dependable rainfall level was used to fin d the wet weeks in each station through out the year. Hargreaves Moisture Availability Index at 60% probability dependable rainfall level was used fo r rainfall onset identification. Farmer survey was conducted to fin d out the existing cropping pattern o f farm ers. The amount o f rainfall, which accumulated on the date o f crop commencement, was assessed using forward accumulation method. • \ The results revealed that mean annual rainfall decreased with time in the Hambantota district. Less than 20% wet weeks were recorded in all stations. It revealed that high risk was involved in rainfed crop cultivation in Hambantota district. Rainfall onset fo r Yala andM aha seasons varied from 12th to 14th week andfrom 38th to 42nd week respectively. The farm ers were able to minimize the irrigation needs o f crops when crop cultivation commenced with the onset o f rain at the given magnitude o f 60% probability. The farm er survey revealed that crop commencement week in M aha season varied between 39th and 41st week and farm ers rarely cultivated during Yala season. According to the forward accumulation method at 75% probability level the amount o f water accumulated at crop commencement time was 75mm. The results indicated that the crop commencement week based on the farm er survey coincided with calculated rainfall onset during M aha season.
