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Understanding the Spatially Variable Effects of Climate Change on Rice Yield for Three Ecotypes in Bangladesh, 1981–2010

Iffat Ara
Department of Geography and Environment, Jahangirnagar University, Savar, Dhaka 1342, Bangladesh

Megan Lewis
School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia

Bertram Ostendorf
School of Biological Sciences, The University of Adelaide, Adelaide, SA 5005, Australia

Abstract/ Executive Summary:

Climate change will impact on rice food security in many parts of the world, including Bangladesh. Little attention has been given to understanding the impact of climate on rice yield for three main ecotypes (Aus, Aman, and Boro) in different areas of the country. The aim of this paper was to analyse the spatiotemporal dynamics of rice yield and climatic variables and the spatially variable climate effects on rice yield for these ecotypes in Bangladesh during 1981–2010 by employing linear mixed models and generalized linear models. The results demonstrated the substantial spatiotemporal variations of rice yield for all ecotypes across the country. Rice yield for ecotypes was more susceptible to temperature changes than rainfall effects. Modelling of a 1⁰ C temperature increase in the country showed strong regional differences in rice yield for these ecotypes. The study concludes that future temperature changes are likely to change regional rice yield for all ecotypes and hence impact food security. The results have important consequences for food security by indicating the need for appropriate region-specific adaptation measures to reduce rice yield variability in the future. The results show the need to consider spatial differences for policy development to improve food security in Bangladesh.

Keywords: Climate Change, Rice Yield, Bangladesh

Location: All over Bangladesh

Start Date: 00-00-1981

End Date: 00-00-2010

Program Area: Risk Management in Agriculture

Non-commodity: Climate change

Objectives:

The specific objectives of the study are (1) to understand the spatiotemporal variations of rice yields for the three main ecotypes and the spatial variations of growing seasons climatic variability of these ecotypes across Bangladesh; (2) to evaluate the spatially variable impacts of climate on rice yield for three rice ecotypes; and (3) to assess regional rice yield changes due to a 1⁰ C temperature increase in Bangladesh.

Methodology:

2.1. Rice Yield Data. Data for rice harvested area in a hectare (ha) for the three different ecotypes Aus, Aman, and Boro and total production of rice at greater districts level (tons) were obtained from the series of Agricultural Statistical Year Books of Bangladesh, published by the Bangladesh Bureau of Statistics (BBS) for the years 1981–2010. These data were then converted to an annual rice yield (tons/ha) for 23 greater districts in the country, dividing the rice production data by the harvested area for the respective ecotype. 2.2. Climate Data. Daily rainfall and maximum and minimum temperature data were sourced from the Bangladesh Meteorological Department for 31 weather stations. Initially, we calculated the daily average temperature of each station from the maximum and minimum temperatures. In the next preparatory step, we calculated the average monthly temperature and monthly average rainfall for all stations. The kriging method was applied to interpolate the station-based climate data. The analysis was conducted using the ArcGIS Version 10.3 Geographic Information System. Finally, we derived 30-year (1981–2010) time series of seasonal average temperature and rainfall for all ecotype and all greater districts, respectively. Note that the climatic season calculation for Boro required consideration of two calendar years (e.g., December 1981 to May 1982 were considered for Boro yield of 1982). 2.3. Analysis. To assess the impact of climate change on the different ecotypes, we developed statistical models relating yield records from the government statistical yearbooks to the environmental conditions in the districts during the study period. We developed separate models for the three ecotypes (Aus, Aman, and Boro), respectively, and we used two model types to assess the impact of climate change at national and district levels. At the national level, we used linear mixed models (LMM) (1) with districts as a random effect in order to evaluate overall changes, yet acknowledging the spatial variability in the models. To assess the overall performance of the models, we estimated a pseudo-R-squared value for generalized mixed effect models using the “r.squaredGLMM” function from the MuMIn package. We report both the marginal and conditional' 2 estimates to distinguish the variance explained for fixed effects compared to overall fixed and random factors in the models, respectively. In order to assess the spatial pattern of rice yield changes across Bangladesh, as affected by a temperature increase, we applied a temperature increase (Δ) to the GLM models by using the standardized relative changes equation (3). These changes are the product of the temperature coefficients -1- from GLM models for the separate ecotypes multiplied by Δ = 1, to assess the impact of a 1⁰ C temperature increase. Standardized rice yield changes (Δ) for all districts are estimated.

Source of Information: Advances in Agriculture Volume 2017, Article ID 6287156, 11 pages

Article Link (Online Journal): https://doi.org/10.1155/2017/6287156

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The objective of the present study was to understand the spatially variable effects of climate change on rice yields for three ecotypes across Bangladesh. Based on past yield observation records, the overall findings reveal that the impact of climatic variables on rice yields is ecotype specific.The results demonstrate that Aman yield may be the worst affected ecotype by a future temperature increase, when compared with the Aus and Boro yields. There is a substantial spatial variability of rice yield sensitivity to a 1⁰ C temperature increase amongst the 23 greater districts. Temperature has adversely impacted Aus and Aman yields in most of the districts compared to an overall positive temperature response of Boro yield. Given this sensitivity to regional rice yield variations, ecotype specific adaptation strategies need to be adopted urgently in different districts to combat future climate change. Priority might be given to the disadvantaged districts where the rice yield will decrease noticeably. Adaptation strategies include the improved dissemination of climate information along with the development and introduction of new temperature tolerant varieties in these districts. However, substantial use of new varieties in different districts needs to be monitored continuously. For this, adequate investment and public private sector involvement will be necessary for a significant time period. The spatially aggregated time series data used in the present study has primarily focused on climate variables alone. Due to a lack of data, the study did not consider other important variables, which contributed to higher yields in many districts during the study period. Therefore, future research should focus on both climate change and other variables to capture a more robust picture of regional rice yields for the ecotypes favored across Bangladesh.

Knowledge Management: Journal