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Long-term Changes in Bright Sunshine Duration in Bangladesh and Its Effects on Crop Evapotranspiration

M. Shahjahan Mondal*
Associate Professor
Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh,

Farzana Nasrin
Professor
M. Sc. Student, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh,

Sinora Zaman
Professor
M. Sc. Student, Institute of Water and Flood Management, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh,

Mollah Md. Awlad Hossain4
Head
GIS Division, Center for Environmental and Geographic Information Services, Gulshan-1, Dhaka-1212, Bangladesh,

Abstract/ Executive Summary:

Solar radiation received by the earth is the primary source of energy which drives the general atmospheric and oceanic circulation and hence the climate system. Any changes in insolation due to natural and anthropogenic factors have important implications for climate change studies as well as agriculture, water resources, and solar energy applications. Solar radiation and sunshine duration are positively correlated. In this study, long-term changes and trends in sunshine duration in Bangladesh are estimated at different time scales: annual, seasonal, monthly and 10-day. Spatial pattern of trends is analyzed. The role of agriculture in solar dimming is also explored through bivariate correlation analysis. To see the combined effect of climatic variables on reference crop evapotranspiration (ET0), all-Bangladesh ET0 time series was determined. The results of the analyses reveal that the sunshine in Bangladesh is decreasing at all time scales – the decrease being higher in the north and west. Agricultural development may have played an important role in this solar dimming. ET0 per unit area is found to be decreasing mainly due to solar dimming and irrigation expansion

Keywords: Trends, Correlation, Sunshine duration, Reference crop evapotranspiration, Cloud coverage, Agricultural development

Location:

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

To observe and study the long-term changes in bright sunshine duration in Bangladesh and its effects on crop evapotranspiration.

Methodology:

Bright sunshine duration data were analyzed at annual, seasonal, monthly and 10-day time scales. Diurnal sunshine duration data were available for 34 stations for a period of 47 years (1961-2007) from Bangladesh Meteorological Department (BMD), Climate Change Cell of Department of Environment, Center for Environmental and Geographic Information Services, and Institute of Water and Flood Management. BMD maintains these meteorological stations and keeps record of the daily climatic variables. There are two methods for analysis of trends in time series data: parametric and non-parametric. Parametric method was used in this study for its simplicity in application. The role of agriculture in dimming via increasing humidity and cloud was explored through correlation analyses. To see the combined effect of the changes in climatic variables on evapotranspiration, reference crop evapotranspiration (ET₀) was estimated using the CropWat software in which FAO Penman-Monteith method is implemented. The method requires the data on maximum and minimum temperatures, air humidity, wind speed and sunshine duration for ET₀ determination. All-Bangladesh values of these variables were estimated from available records at 34 stations of BMD. Ten-day average ET₀ was estimated using 10-day average climatic data.

Source of Information: 2nd International Conference on Water & Flood Management (ICWFM-2009), BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Sunshine duration is found to be shortening all over Bangladesh. The declining trends in the winter, dry season, summer and monsoon seasons are 5.7%, 5.0%, 3.9% and 3.8%, respectively, in every 10 years for entire Bangladesh. The overall annual decrease is 4.7% a decade. There is a spatial pattern in the declining trends – the trends increase from south to north and from east to west. This trend is positively correlated with the general rainfall distribution pattern of the country. Though cloud coverage is found to have slightly increased in the country, the increase is not large enough to account for the decrease in sunshine. Changes in cloud attributes and/or increases in water vapor in the atmosphere may have significant roles in the observed dimming. The all-Bangladesh ET0 time series indicates that ET0 is decreasing, which is in contrary to the general belief and many study findings that due to global warming ET0 and hence irrigation water demand would increase

Knowledge Management: Report/Proceedings