Spatial variability of climate change impacts on Rice (Oryza sativa L.) yield in Kerala

Abstract

Rice is one of the essential food crops of the world. Almost 40% of the world’s population consumes rice as their staple food. Nearly 12% of the total cultivated area in Kerala accounts for rice cultivation. It is cultivated in both plains and high altitudes, therefore long-term climatic changes within a region and their impact on productivity is very important. Crop weather models have a vital role in climate change studies. Rice studies are mainly carried out in the CERES- Rice (Crop Environment Resource Synthesis- Rice) model. The CERES - Rice has been calibrated and validated and found suitable for simulation of rice growth and development in the tropical humid climate. The present experiment was aimed to study the impact of climate change on phenophase and yield aspects of rice varieties under climate change scenarios of RCP 4.5 and 8.5 in 14 districts of Kerala. Short-duration rice variety, Jyothi and medium-duration variety, Jaya have been selected for the experiment. The experiment was carried out with the split-plot design. The main plot treatments were five dates of plantings (June 5 th , June 20th , July 5 th , July 20th and August 5 th) and subplot treatments were two varieties (Jyothi and Jaya) with four replications. Various observations like weather, phenological, biometric, physiological, yield and yield attributes had been recorded to studythe crop weather relationship. The crop weather analysis has been carried out with SPSS software. The results indicated that duration of phenophases had a negative correlation with the maximum temperature. A significant variation in the biometric observations was also obtained. Plant height and dry matter accumulation were found to be higher in Jyothi when compared to Jaya. Both varieties recorded the maximum leaf area index (LAI) and leaf area duration (LAD) at 75 days after planting. The crop growth rate was obtained maximum at an interval of 45 to 60 days after planting irrespective of the variety. The highest grain yield in Jyothi was obtained during June 5th and August 5th plantings which were found to be on par. In Jaya, July 20th planting and August 5 th planting were found to be on par. Using the observations from the field, validation of genetic coefficient of DSSAT- CERES model. To study the impact of climate change on rice production, climate change in Kerala had been estimated. The current climate (1980 – 2020) has been compared with three different future 2010-2030 (near-century), 2021-2050 (mid-century) and 2051-2080 (latecentury) simulations for the 14 districts of Kerala under Representative Concentration Pathway (RCP) 4.5 and 8.5. The annual and seasonal (southwest monsoon, northeast monsoon, winter and summer season) comparison of weather data has been carried out. Under RCP 4.5 the amount of solar radiation is expected increase by greater than 1 MJ/m2 districts like Wayanad, Malappuram, Thrissur, Ernakulam, Kottaym and Pathanamthitta by the end of century. Under RCP 8.5 a normal departure (-1 to 1 MJ/m2 ) is expected by the end of century in most parts except in Wayanad and Thrissur, where an above normal increase is predicted. At the same time in Palakkad a below normal decrease is expected in solar radiation. During the southwest monsoon an increase in solar radiation is expected in mid-century and by the end of century a normal departure is expected except in Malappuram, Palakkad and problematic zone where the solar radiation is expected to increase. Under RCP 8.5 a normal departure is expected by the end of century except in Kasargod, Kozhikode, Wayanad and Thiruvananthapuram where a below normal departure is expected. In northeast monsoon season solar radiation is expected to increase in central and problematic zone and a normal departure is expected in other parts under RCP 4.5. In RCP 8.5 by the end of century solar radiation is expected to decrease in Kozhikode, Idukki and Thiruvananthapuram during northeast monsoon. An increase in solar radiation is expected in central, problematic and southern zone during RCP 4.5 in winter season while in northern zone solar radiation is expected to be normal in RCP 4.5 and a below normal departure is expected in RCP 8.5. In Thiruvananthapuram a solar radiation is expected to decrease in both scenarios. A normal departure of solar radiation is expected to increase in most parts of Kerala during the summer season. In Kannur, Kozhikode, Thiruvananthapuram and Wayanad solar radiation are expected to decrease by -1.5 MJ m2 or less than that by the end of century under RCP 8.5 except in Malappuram where an above-normal increase is expected. An increasing trend in maximum and minimum temperature is expected in future simulations. The annual temperature is expected to increase in all parts of Kerala except in Idukki where a below normal departure (-1.5 to 1.5°C) is expected in near and mid-century. By the end of century a normal departure of annual maximum temperature is expected in high range zone and Thiruvananthapuram under RCP 4.5 and while under RCP 8.5 only Idukki and Thiruvananthapuram is showing a normal departure. In southwest monsoon season temperature is expected to rise by 1.5°C by end of century under RCP 8.5 while under RCP 4.5 a normal departure is expected in Wayanad, Idukki and Kollam. During the northeast monsoon season and summer season the maximum temperature is expected to increase in all parts expect in Idukki in near and mid-century under both RCPs. In RCP 4.5, a normal departure of annual maximum temperature is projected in the high range zone and Thiruvananthapuram by the end of the century, but only Idukki and Thiruvananthapuram will show a normal departure under RCP 8.5. During the winter season a decrease in temperature is expected in Idukki while in other districts the temperature is expected to increase. The minimum temperature is expected to increase in Kerala except in Idukki in all the future simulations under both RCPs in all seasons. In Idukki the minimum temperature is expected to decrease in near century and then increase in mid and end of century with a normal depature. A spatial variation in rainfall is expected in Kerala in future simulations, with an excess or normal rainfall in some parts at the same time deficiency in other parts of Kerala. The annual rainfall is expected to increase in most parts of Kerala. In districts like Kasargod, Idukki and Alappuzha a normal departure (+19 to -19%) in annual rainfall is expected in all the future simulations under RCP 4.5 ad 8.5. During the southwest monsoon season, rainfall is expected to show a large excess and excess in most parts of Kerala except in Kasargod where a normal departure is expected. Under RCP 4.5 the rainfall is expected to decrease in Wayanad and Alappuzha by the end of century. While under RCP 8.5 the rainfall is expected to increase in Wayanad and Thiruvanathapuram by the end of century. Northeast monsoon is expected to be show a normal departure in most places. Under RCP 4.5 it is expected to decrease in Idukki, Pathanamthitta, Kollam and Kasargod. While under RCP 8.5 it is expected to increase in Ernakulam, Alappuzha, Pathanamthitta and Kollam at the same time a deficit rainfall is expected in Kannur and Thrissur. Winter rainfall was predicted to decrease from normal in almost all parts of Kerala in near and mid-century. By the end of century under RCP 4.5 and by mid and end of the century under RCP 8.5 and excess rainfall is predicted in parts of the northern zone and problematic zone. Summer rainfall is expected to be large excess and excess in most parts during near and mid century under RCP 4.5 and in the near century of RCP 8.5. In the end of century under RCP 4.5 and in mid and end of the century under RCP 8.5 a normal rainfall is expected in most places. In Idukki and Thiruvananthapuram the rainfall is expected to be deficient. The potential yield had been predicted with the DSSAT- CERES model using the genetic coefficient validated using field experiment. the predicted weather for 13 districts of Kerala. The duration of crop is expected to decrease as a result of increase in temperature in both varieties. Yield reduction is expected in future simulations under both the RCPs in most places of Kerala. Under RCP 4.5 in Jyothi, June 5th planting showed maximum deviation from base period (2020). The maximum deviation was observed in Kozhikode i.e. in near (-58%), mid (-63%) and end of century (-60%) under RCP 4.5 and in near (- 62%), mid (-60%) and end of century (-64%) under RCP 8.5. The least deviation was found in July 20th planting in all the future simulations. In Idukki, an increase in yield had been observed in July 5 th , July 20th and August 5 th plantings. An increase by 34%, 28% and 23% in near, mid and end of century respectively is expected. Under RCP 8.5 in July 20th planting higher yield has been observed and shows a positive deviation of 38%, 28% in near and mid century respectively in Idukki. By the end of century yield is expected to decrease except in August 5th planting which showed a positive deviation of 12%. In southern zone the highest potential yield had been observed in August 5 th planting. In Jaya also the maximum deviation had been observed during June 5th palnting in Kozhikode i.e. in near (-58%), mid (- 63%) and end of century (-60%) under RCP 4.5 and in near (-62%), mid (-60%) and end of century (-64%) under RCP 8.5. In Idukki under RCP 4.5 an increase in yield was observed during July 20th planting with an increase by 27% in near and mid century and by the end of century a deviation of 20% was observed. Under RCP 8.5 in July 20th planting higher yield has been observed and shows a positive deviation of 27%, 24% and 10% in near, mid and end of century. In southern zone of Kerala, highest potential yield of Jaya has been observed in July 20th planting in all the future simulations under both RCPs. The duration of crop showed a negative correlation with the temperature. As a result decrease in duration of phenophase had been observed in future simulations. An increased temperature and precipitation patterns during panicle initiation to anthesis may be the reason for the yield variability. During the base period higher yield was obtained during June 5th and June 20th planting i.e. early plantings while in future simulations the higher yield is expected in July 5th, July 20th and August 5th plantings i.e. late plantings. Hence there is a chance of shift in date of planting in Kerala in future.