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Projections of On-farm Salinity in Coastal Bangladesh

D. Clarkea
Faculty of Engineering and the Environment, University of Southampton,Southampton, SO17 1BJ, United Kingdom

S. Williamsa
Faculty of Engineering and the Environment, University of Southampton,Southampton, SO17 1BJ, United Kingdom

M. Jahiruddin
Department of Soil Science, Bangladesh Agricultural University,Mymensingh, Bangladesh

K. Parks
Faculty of Engineering and the Environment, University of Southampton,Southampton, SO17 1BJ, United Kingdom

M. Salehin
Institute of Water and Flood Management, Bangladesh University ofScience and Technology, Dhaka-1000, Bangladesh

Abstract/ Executive Summary:

This paper quantifies the expected impacts of climate change, climate variability and salinity accumulation on food production in coastal Bangladesh during the dry season. This forms part of a concerted series of actions on agriculture and salinity in Bangladesh under the UK funded Ecosystems for Poverty Alleviation programme and the British Council INSPIRE scheme. The work was undertaken by developing simulation models for soil water balances, dry season irrigation requirements and the effectiveness of the monsoon season rainfall at leaching accumulated salts. Simulations were run from 1981 to 2098 using historical climate data and a daily climate data set based on the Met Office Hadley Centre HadRM3P regional climate model. Results show that inter-seasonal and inter-annual variability are key factors that affect the viability of dry season vegetable crop growing. By the end of the 21st century the dry season is expected to be 2-3 weeks longer than now. Monsoon rainfall amounts will remain the same or possibly slightly increase but it will occur over a slightly shorter wet season. Expectations of sea level rise and additional saline intrusion into groundwater aquifers mean that dry season irrigation water is likely to become more saline by the end of the 21st century. A study carried out at Barisal indicates that irrigating with water at up to 4 ppt can be sustainable. Once the dry season irrigation water quality goes above 5ppt, the monsoon rainfall is no longer able to leach the dry season salt deposits so salt accumulation becomes significant and farm productivity will reduce by as a much as 50%, threatening the livelihoods of farmers in this region.

Keywords: Projections, On-farm salinity, Coastal area, Bangladesh

Location: The region around Barisal

Start Date: 00-01-1981

End Date: 00-12-2098

Program Area: Resource Development and Management

Non-commodity: Adoption and mitigation technology

Objectives:

The work was undertaken by developing simulation models for soil water balances, dry season irrigation requirements and the effectiveness of the monsoon season rainfall at leaching accumulated salts. Simulations were run from 1981 to 2098 using historical climate data and a daily climate data set based on the Met Office Hadley Centre HadRM3P regional climate model.

Methodology:

The region around Barisal was selected as a study area because it lies in the transition zone of soil salinity problems. The dry season soil salinity in Barisal is relatively low (~2 dSm^-1) but nearby areas are becoming affected by increasing salinization eg Bhola (~4 dSm^-1) and Jhalokati (~6 dSm^-1). Barisal has a long climatic record and is included in the FAO CLIMWAT 2 climatic database28. A daily soil moisture deficit (SMD) model was constructed for the Barisal region between 1981 and 2098. SMD is defined as the amount of water in units of mm of rain (or irrigation) required to rewet a dry soil so that the plant root zone is at field capacity (i.e. it can hold no more water). The model is based on the FAO CROPWAT single layer approach29. It requires daily values of rainfall and potential evapotranspiration, crop characteristics (crop type, rooting depth and crop coefficient) and soil characteristics (soil type, structure and porosity). Daily precipitation values for 1981-2098 were provided by a 17 member ensemble of simulations of the HadRM3P (PRECIS) regional climate model developed by the Met Office Hadley Centre.30 The model is based on the HadCM3 global climate model and dynamically downscaled to assess regional climate variability.31 The model runs at a 0.22° x 0.22° resolution (~25 km by 25 km), with 19 vertical levels and 4 soil levels32. The ensemble member (labelled Q0) represents an unperturbed version of the model physics. The projections are driven by the Special Report on Emissions Scenario (SRES) A1B scenario33, which lies between RCP6.0 and RCP8.5 in terms of atmospheric CO₂ concentrations and global temperature projections34. This represents a future for the coastal areas in Bangladesh which is approximately 4^oC warmer and 9% wetter by the year 2098. This paper reports results from the unperturbed model Q0. Two alternate scenarios were used to examine the sensitivity of the models developed, one which is warmer and drier (Q8) another which is warmer and wetter (Q16) 30. The differences between the salinity accumulation due to the three climate scenarios is discussed at the end of the paper.

Source of Information: Environmental Science: Processes & Impacts., 2015, 00, 1-11

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Results showed that inter-seasonal and inter-annual variability are key factors that affect the viability of dry season vegetable crop growing. By the end of the 21st century the dry season is expected to be 2-3 weeks longer than now. Monsoon rainfall amounts will remain the same or possibly slightly increase but it will occur over a slightly shorter wet season. Expectations of sea level rise and additional saline intrusion into groundwater aquifers mean that dry season irrigation water is likely to become more saline by the end of the 21st century. A study carried out at Barisal indicates that irrigating with water at up to 4 ppt can be sustainable. Once the dry season irrigation water quality goes above 5ppt, the monsoon rainfall is no longer able to leach the dry season salt deposits so salt accumulation becomes significant and farm productivity will reduce by as a much as 50%, threatening the livelihoods of farmers in this region.

Knowledge Management: Journal