Climate Change in the Brahmaputra Valley and Impact on Rice and Tea Productivity

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Given the vulnerability of agricultural sector to variations in weather conditions, it will be one of the sectors most affected by climate change. This study assesses the state of climate change and variability in the Brahmaputra valley of India and consequent implications on productivity of two important crops rice and tea grown extensively in the valley. The trends and fluctuations of the major climatic variables were assessed using statistical techniques. A quantitative assessment of the impact of observed as well as projected climate on rice and tea productivity was carried out in the study area through statistical and process-based simulation models. Historical rainfall data from 1901 temperature data from 1951 and sunshine duration data from 1971 were analyzed for assessing long-term trends. A suite of climate change indices derived from daily rainfall (1955 and temperature (1971 data, with a primary focus on extreme events, were computed and analyzed to understand the trends. The impact of climate change and its variability on yield patterns of rice and tea were based on 26 years of district level rice yield data (1985 and 20 years of estate level tea yield data (1991 The CERES-Rice crop simulation model was used to predict rice yield under future climate scenarios. The likely impact of future climate changes on tea yield was based on the statistical models developed for monthly yields and climate data of 1991 to 2010. Annual and monsoon rainfall in the study area exhibited a weak diminishing tendency during 1901 due to significant decrease in rainfall in the eastern part of the valley. Significant declining trend of monsoon rainfall during the recent 30-year period was due to significant decrease of July and September rainfall and this trend was consistent at different spatial scales. The intensity of monsoon rainfall was found to diminish over the entire valley due to decrease in the extreme fractions of rainfall, marked by extremely wet, very wet and moderately wet days during the recent three decades (1981 Decrease of rainfall fraction due to moderately wet days was particularly significant in the eastern and western parts of the valley. Rainfall during pre-monsoon and post monsoon season showed increasing tendency during the most recent 30-year period due rise in extreme rainfall indices over the valley. Increase of rainfall during pre-monsoon was primarily contributed by significant increase of April rainfall in the western part of the valley.
Supervisor: Mrinal Kanti Dutta