Adapting to Climate Change

Strengthening the Climate Resilience of Water Sector Infrastructure in Khulna, Bangladesh

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• Publisher: Asian Development Bank
• Year: 2011
• Print ISBN: 9789290922483
• eBook ISBN: 9789290922728
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Global Warming & Climate Change
• Index: Biological Sciences

Climate change and the resulting rise in sea level would affect water sector infrastructure, such as surface water supply and urban drainage systems. The climate resilience of such infrastructure should then be made more climate-resilient to optimize its expected benefits. This publication provides a specific example of assessing the impacts of climate change on the water sector infrastructure in Khulna, Bangladesh, by developing the climate change and socioeconomic development scenarios for 2030 and 2050, and running mathematical models to obtain the level of salinity in river water---where the proposed intake for water supply is located---and the extent of waterlogging in the city. The study then identifies and makes a financial evaluation on adaptation options to cope with the impacts. While various uncertainties still remain, the proposed investments would be made more climate-resilient by incorporating adaptation options into the project design.

Study Approach and Methodology

To assess climate change risks and impacts for Khulna, the study (i) made climate change projections for Khulna for 2030 and 2050; (ii) developed socioeconomic development scenarios for Khulna for 2030 and 2050; (iii) developed and calibrated three mathematical models; (iv) ran the models for 2030 and 2050, using the climate and socioeconomic changes projected; (v) assessed impacts through geographic information system mapping; and (vi) identified and analyzed adaptation options. A flow diagram showing this approach and work flow is in Figure 3.

Figure 3 Flow Diagram of the Study

GDP = gross domestic product.

Source: Adapted from ADB.

Climate Change Projection

Climate

Two greenhouse gas emission scenarios, A2 and B1, from the Special Report on Emissions Scenarios by the Intergovernmental Panel on Climate Change (IPCC) were used because they represent the high and low brackets of the estimated global temperature increases under the report story lines.⁹ A2 is the business-as-usual scenario, a very heterogeneous, market-led world, with high population growth, slow economic development, and slow technological change. B1, however, is the sustainable development scenario, a convergent world with rapid changes in economic structures toward a service and information economy, with resulting lower greenhouse gas emissions.

Statistical downscaling was then undertaken from a Global Climate Model (ECHAM5/MPI-OM)¹⁰ to a finer resolution (0.5° x 0.5°), mainly because of the time available for the study. The model outputs were bias-corrected for rainfall and temperature.¹¹ The findings are outlined in Table 1.

Table 1 Summary Features of Climate Projections for Khulna

Scenario	A2	B1
Temperature	The average monthly temperature rise by 2050 varies from +0.5°C in October to +1.7°C in January and February.	The average monthly temperature rise by 2050 varies from +0.5°C in June, July, and August to +1.5°C in February and April.
Rainfall	The annual rainfall increases by about 5.0% by 2050 (1,860 mm per year) from the reference period.^a	The annual rainfall increases by about 9.3% by 2050 (1,739 mm per year) from the reference period.^b
Seasonal rainfall	Increase in July-September by 4.6% and a decrease in December-February by 26.3%	Increase in July-September by 10.5% and a decrease in December-February by 46.2%.^c
Rainfall intensity	50 mm or more rainfall in 6 hours increases from 4.20 times per year to 5.90 times per year in 2050.	50 mm or more rainfall in 6 hours marginally increases from 4.20 times per year to 4.25 times per year in 2050.

C = Celsius, mm = millimeter.

^a The value is compared with 1,769 mm, the average annual rainfall from 2001 to 2020 projected in the model under the A2 scenario, and thus is different from the observed value (1,924 mm from 2004 to 2009) in the past. The observed value is higher than the projected value. The historical observed average between 1985 and 2009 is 1,887 mm.

^b The value is compared with 1,591 mm, the average annual rainfall from 2001 to 2020 projected in the model under the B1 scenario, a much lower figure than the observed value.

^c A higher degree of increase and decrease under the B1 scenario in comparison to that under the A2 scenario is different from what one normally expects. Due to the interannual and decadal variability and chaotic nature of atmospheric process, individual model runs can result in different changes in rainfall. Therefore, these differences are considered within the margin of error and do not necessarily mean that there will be higher variation under the B1 scenario.

Source: Adapted from ADB.

These results are, however, based on the outcomes of a single Global Climate Model. Other models indicate similar changes, but there are still considerable uncertainties about the possible change in rainfall in Bangladesh.

Sea-Level Rise

As for the rising sea levels, two different levels (i.e., plausible high and plausible low) were used in the different model runs, due to high uncertainty of the levels. The plausible-low scenarios, 10 centimeters (cm) in 2030 and 20 cm in 2050, are about midrange in the IPCC scenarios. The plausible-high scenarios, 25 cm in 2030 and 40 cm in 2050, assume significant melting of land ice. This is in line with the findings of recent new models and research, which indicate that the contribution of melting land ice to rising sea levels may be substantially more than what IPCC projected (footnote 9).

River Discharge

Another important factor is the intake discharge of the Gorai and Arial Khan rivers from the Ganges and Padma rivers, respectively. As it was not possible in the study to develop a hydrological model for the complete Ganges and Brahmaputra basins to determine future discharge rates, the output of the same Global Climate Model (ECHAM5/MPI-OM) on the runoff changes of the Ganges and Brahmaputra basins was used. Under both the A2 and B1 scenarios, the intake discharge of the Gorai and Arial Khan rivers is reduced in 2030 and 2050 during most of each year, except in October (i.e., the end of the rainy season) when the discharge is increased.

Socioeconomic Scenario Development

For the study, numerous assumptions were made regarding Khulna’s socioeconomic scenarios in 2030 and 2050. Socioeconomic surveys, various census data, literature reviews, and discussions with relevant agencies and experts were the basis of scenario development. Key parameters are shown in Table 2.

Table 2 Key Parameters for Socioeconomic Development

Parameter	Assumption	Remarks
Population in KCC area	2% growth per year: (i) 976,000 in 2010; (ii) 1,450,000 in 2030; and (iii) 2,155,000 in 2050	Population distribution among the 31 wards was assumed to be maintained.
Water demand	Per capita domestic demand of 120 liters per day in 2030 and 150 liters per day in 2050	100% of the population in the KCC area will be served by the proposed water supply system.
GDP growth rate	6.2% per year	The national average rate of growth between 2001 and 2009 was 6.2%.
Urban development	Proportion of impervious areas (weighted average): (i) 17.7% in 2010, (ii) 29.0% in 2030, and (iii) 38.7% in 2050	For each subcatchment area, a change in the proportion between pervious and impervious areas was projected.

GDP = gross domestic product, KCC = Khulna City Corporation.

Source: Adapted from ADB.

Hydraulic Models Development

Three mathematical models were developed and/or calibrated to assess the impacts of climate change for the study. The roles of these models—the Southwest Regional Hydrodynamic Model, Salinity Model, and Urban Drainage Model—are shown in Figure 4, and the main features of each model are given in Table 3.

Figure 4 Model Framework

Source: Adapted from ADB.

Table 3 Features of the Three Mathematical Models

IWM = Institute of Water Modelling, KCC = Khulna City Corporation, TA = technical assistance.

^a Mike 11 is a software program that could simulate flow and water level, water quality, and sediment transport in rivers. Mike 11 is a one-dimensional model.

^b Mike Urban is a geographic information system-based urban water ...

Table of contents

• Front Cover
• Title Page
• Copyright Page
• Contents
• Tables and Figures
• Acknowledgmensts
• Abbreviations
• Weights and Measurements
• Introduction
• Study Approach and Methodology
• Estimating Impacts on the proposed Surface Water Supply Systems
• Estimating Impacts on the Current and Proposed Urban Draining System
• limitations and Conclutions
• Footnotes
• Back Cover