Key Words: Global warming, crop production, Crop simulation model, Spatial-EPIC
Abstract
Agriculture is always vulnerable to unfavorable weather events and climatic conditions. Despite technological advances such as improved crop varieties and irrigation systems, weather and climate are still key factors in agricultural productivity. Often the linkages between these key factors and production losses are obvious, but sometimes the linkages are less direct. The impacts of climate change on agricultural food production are global concerns, and they are very important for Bangladesh. Agriculture is the single most and the largest sector of Bangladesh's economy which accounts for about 35% of the GDP and about 70% of the labor force. Agriculture in Bangladesh is already under pressure both from huge and increasing demands for food, and from problems of agricultural land and water resources depletion. The prospect of global climate change makes the issue particularly urgent. It is well established that atmospheric concentration of CO2 is increasing and this would be beneficial for crop growth and productivity. But the nature and magnitude of climatic change associated with the increase of CO2 and other radioactive trace gases are uncertain. Thus, it is difficult to predict the combined impact of increasing atmospheric CO2 on agricultural productivity. Crop simulation models are used widely to predict the crop growth and development in studies of the impact of climatic change.
So far, climate-based models for estimating potential productivity are used for this purpose. These models are relatively easy to apply, but they fail to estimate actual productivity and possible effects of mitigation measures. On the other hands, process-based crop models are advantageous to estimate actual productivity, but they are applied to only limited numbers of test sites due to heavy data requirement in applying them for wide areas.
A comprehensive GIS-based biophysical crop simulation model, Spatial-EPIC, was used in order to demonstrate the crop growth response to the combined effects of CO2 concentration increase and CO2-induced climate change at the national level. Modeling within a GIS offers a mechanism to integrate the many scales of data developed in and for agricultural research. Rice and wheat cropping system in Bangladesh were studied for this purpose.
Introduction
The balance of scientific evidence now suggests that over the last century humans have begun to have a discernible influence on the earth's climate, causing it to warm (IPCC, 1996, 1998). Since the beginning of the industrial age, the concentration of CO2 in the atmosphere has increased from 280 to 350 parts per million (Bazzaz and Fajer, 1992). The increase of CO2 in the atmosphere has been more rapid in recent years. The major reason for this increase may be attributable to the extensive use of fossil fuels, such as oil, coal and gas. The destruction of carbon sink by excessive land use and deforestation might be another important cause for the atmospheric CO2 increase over the last 100 years (Houghton et. al., 1990). It has been projected from the historical data and simulation models that the CO2 level in the atmosphere will reach 600 ppm in the last half of this century (Strain, 1987). The increase of CO2 and several other green house gases such as methane, nitrous oxide, chlorofluorocarbons (CFCs) could cause an increase global temperature of about 4.2°C and possibly a change in precipitation patterns and amounts in some regions (Kimball et. al., 1993). Global warming due to increasing concentrations of green house gases poses a threat to human society by changing the living and working environment to which society has adapted over many generations (Jodha, 1989). Agricultural impacts of climate change could have profound effect in poor and developing countries.
Bangladesh, a developing country in South Asia, is primarily a deltaic flood plains, and elevations in most of the country do not exceed 10m. The country has a humid tropical climate. Average rainfall in drier and wetter regions are 1500mm and 5000mm per year respectively. In winter, the average minimum and maximum daily temperatures are about 9.7 and 26.6°C respectively. In the summer, the average maximum temperature is about 32.2°C (BARC, 1991). Despite technological advances such as improved crop varieties and irrigation system, weather and climate are still key factors in agricultural productivity. The rise of CO2 level in the atmosphere and the concomitant climate change will have a direct impact on agriculture. It is generally well accepted that this increase will have beneficial effects on plant productivity. What remains most uncertain is the nature and magnitude of the climate changes that will occur as a result of the increase of CO2 and other radioactively trace gases. Thus it is difficult to predict the combined impact on agricultural productivity. Crop simulation models can be used predict the impact. These models can provide a way to estimate crop production under climate-change condition. Research on crop simulation has concentrated on determining the relationships between crop growth, yields and environmental variables through field experiments as well as simulated experiments. Geographic Information System (GIS) provide another technology for crop modeling researches. GIS is a unique tool on solving spatial related problems. In recent times, several scientists/researchers have attempted to link crop models with GIS. For the research purpose of this paper, a spatial biophysical crop model- "Spatial-EPIC" (Satya et. al., 1998) is chosen. This model is the modification of EPIC (Erosion Productivity Impact Calculator) developed by USDA/ARS, which offers a spatial dimension to the original one.
