Assessment of the suitability of temperature and relative humidity for rice cultivation in rainfed lowland paddy fields in Kurunegala district

Climatic suitability analysis is a prerequisite to achieve optimum utilization of the available resources in rainfed rice cultivation. Therefore, a study was conducted to assess the climatic factors and to map their suitability for rainfed paddy farming in Mahananeriya, Ibbagamuwa and Alawwa ASC regions representing dry, Intermediate and wet areas of Kurunegala District in Yala and Maha seasons using Geo-Informatics. Daily weather data of maximum temperature, minimum temperature, and relative humidity for 10 years were averaged on a weekly basis. The IDW interpolation technique was used to prepare thematic maps. The maximum temperature was grouped as 270C - 320C, 320C - 350C, and more than 350C. The minimum temperature was grouped as less than 190C and more than 190C. Relative humidity was grouped into three classes as 60% - 80%, 80 % - 85% and more than 85%. The temperature maps and relative humidity maps were overlaid with the weighted sum technique giving weights as 0.75 and 0.25 respectively to produce suitability maps for rice cultivation on weekly basis throughout the year. Results show that minimum temperature is not in the critical level for rice cultivation within Kurunegala District throughout the year. Maximum temperature is optimum (270C - 320C) for rice cultivation in all three ASC regions during Maha season and in Ibbagamuwa and Alawwa ASCs during Yala season. Relative humidity in all three ASCs is more than 85% during Maha season and in between 80 % and 85 % during Yala season. Considering temperature and relative humidity, whole rainfed paddy lands in Ibbagamuwa and Alawwa ASCs are highly suitable for rice cultivation in the Yala season. Rainfed paddy lands in all three ASCs are in suitable category in terms of the suitability of temperature and relative humidity during Maha season. Spatial variations of the suitability of the interactive outcome of the maximum temperature and relative humidity appear among Mahananeriya, Ibbagamuwa and Alawwa ASC regions representing Dry (DL1b), Intermediate (IL1a) and Wet (WL3) zones in Kurunegala District. Intra regional spatial variations are very rare. Temporal variations among two seasons of Yala and Maha and the intra variations within the seasons also evidence. Date of seed sowing or crop establishment should be aligned according to the suitability levels matching with the flowering and grain filling stages of rice.