Climate change impact on crop water requirement of rice in Thrissur district

Abstract

Rice crop occupies a major position in the agricultural production in Kerala State. Under the present climate change scenarios the climatic parameters are subject to variations and that in turn will affect the water requirement of the crop. A great stress on the irrigation reservoirs and projects for additional water to be released will be effected. It was attempted to generate the climate data for 2030, 2050, 2080 under IPCC emission scenarios RCP.45.The crop water requirement for rice was calculated under the predicted climate for Thrissur district using CROPWAT model. The minimum temperature in the district were found to increase during the future years. The maximum temperature also showed an increasing trend through the future years. The summer months January – March were found to remain as the hot months during the predicted years. The solar radiation was also found to increase. The average annual rain fall for Thrissur district was found to vary as 3139.1, 3089.8 and 3307.6 mm for the future years of 2030, 2050, 2080. The onset of south west monsoon may become early. The summer rains will continue to give a good amount of rain fall through the future years. There will be a reduction in the post monsoon rain fall and a poor distribution of rain fall over the district. The crop evapotranspiration in all the three rice growing seasons of virippu, mundakan and punja was found to increase under the predicted scenario. Crop evapotranspiration was found to increase from 49.99 mm during 2015 to 61.27 mm during 2080 in the first crop season (virippu). During the second and third crop season (mundakan and punja) crop evapotranspiration varied from 56.53 mm to 82.17 mm and 77.06 mm to 83.17 mm respectively. When compared to the year 2050 the irrigation water demand was found to decrease during the year 2080. During the first crop season the irrigation water demand will increase to 319.6 mm in the year 2050 and later during 2080 it was found to decrease to 265.6 mm. There will be a considerable increase in the water requirement during the second crop season during 2050’s and 2080’s when compared with the present day demand. It was also indicated that under RCP 4.5 scenario the water demand to the rice crop during second crop season will be more by 100 mm of water.The crop water use efficiency was found to decrease during future years. An additional amount of 200 billion litres of water will be required for meeting increased water requirement during the second crop season for irrigating rice. The requirement for the third crop season will be high as 750 billion litres.