Cost-bene ﬁ t of promising adaptations for resilient development in climate hotspots: evidence from lower Teesta basin in Bangladesh

It is very likely that climate change will increase the frequency and intensity of extreme events such as ﬂ oods, ﬂ ash ﬂ oods, storms, heat and cold waves, riverbank erosion, and drought in the river basin of Hindu Kush Himalayan (HKH) region. This could mean detrimental impacts to the poor and marginal people in the lower Teesta basin (LTB) in Bangladesh. Though adaptation involves ﬁ nancial costs, the farmers ’ practicing adaptation in LTB experience diminished crop loss and damage. This study was aimed at assessing the promising adaptation practices, their economic return, and social welfare in the LTB through an extended cost-bene ﬁ t analysis. The study suggests that among the adaptations, shallow tube-well (STW) based irrigation practice in both sandy and loamy soil has the highest marginal adaptation cost (MAC) but the lowest bene ﬁ t-cost ratio (BCR). The deep tube-well (DTW) based irrigation practice generates superior bene ﬁ ts to the farmers compared to the STW based farming due to initial establishment by the government which is very expensive. Maize farming as an alternate and less resource consumptive cropping produces nearly ﬁ ve times higher economic bene ﬁ ts than the costs which can be acknowledged as the most pro ﬁ table and resilient adaptation option in the LTB. Though MAC is relatively low for the short-duration variety (SDV) rice among the promising adaptations, its economic pro ﬁ tability is 62% lower than that of the maize cultivation. However, having higher BCR the maize cultivation generates US$86 higher welfare to the farmers than the SDV rice which may strengthen the farmer ’ s preference of maize cultivation over the SDV rice. It can be stated with high con ﬁ dence that strategic adaptation planning, soft credit, technological advancement, and subsidized agricultural inputs will encourage the farmers to carry out adaptation options which may reduce climate-induced loss and damages for the farmers and build socio-economic resilience in the LTB and other similar areas of South Asia.


INTRODUCTION
Climate change poses several risks to agricultural production, livelihood sectors, ecosystem services flow, and economic prosperity at national, regional and global scale  ADB ). Apart from these national efforts and initiatives, community-level adaptations are also very crucial to build climate resilience at the micro-level (Chambwera et al. ). Though there are a good number of success stories available at the grassroots level adaptations, the financial and social benefit and cost-related information of these adaptation practices are largely unknown which obstructs the integration between micro and macro-level adaptation planning. In this circumstance, this study dedicates its effort to generate evidence-based versatile knowledge on community-level adaptation options and their costeffectiveness and socio-economic viability in the LTB in northwest Bangladesh.
To attain this objective, our study has examined the most promising adaptation practices, their economic cost and socio-economic benefit in the LTB where the communities frequently affected by multiple climatic stressors.
Then we estimated the magnitude of farmers' welfare and opportunity cost and benefit of adaptations for in-depth assessment and evidence generation. As costs and benefits of adaptation options are very worthy nowadays to assist planners and practitioners in identifying the most suitable interventions for reducing micro-level vulnerability and advancing resilience (WB ; ADB ; Westphal et al.

;
ECONADAPT ). This study has adopted an extended Cost-Benefit Analysis (CBA) approach in examining the socio-economic feasibility of promising adaptations in the LTB and addresses their policy aspects for upscaling and out scaling for wider progress in development. Further, the study develops an adaptation decision support matrix containing the diversified information on social and economic aspects of widely practiced micro-level adaptation options which will enable farmers, institutions and policymakers to profitable adaptation-led resilience planning for combating climate change impacts in the agriculture sector of Bangladesh and HKH region as well. This study would further contribute to the policy planning of upscaling and out-scaling of the adaptation practices at other regions of the Global South.

MATERIALS AND METHODS
We have adopted the methodology developed by WB () to evaluate the cost-benefit of promising climate change adaptations in the LTB in Bangladesh. When assessing the costs and benefits of adaptation options, many approaches are proven to be effective in the broader context of national, regional, sectoral and micro-level planning and management (WB ). According to the UNFCCC () and GCCASF (), three most commonly used techniques for adaptation assessment are: (i) cost-benefit analysis (CBA); (ii) cost-effectiveness analysis (CEA); and (iii) multi-criteria analysis (MCA).
CBA assesses the benefits and costs of adaptation options in monetary terms. Whereas CEA identifies the least-cost option of reaching an identified target/risk reduction level or the most effective option within available resources, MCA assesses adaptation options against several criteria, which can be weighted, to arrive at an overall score.
Apart from CBA, CEA, and MCA, several approaches such as strategic environmental assessments (SEA), environmental impact assessments (EIAs), risk-based approaches, and the Delphi method are also used for adaptation evaluation. As our paper intends to examine the financial and social feasibility of adaptation through the quantitative lens, the CBA method along with decision-support matrix and real benefit measurement approaches are used to scrutinize the most practiced adaptation options in the LTB of Bangladesh.
Typically, CBA accounts for the economic return of different projects, programs, interventions or policies to be compared in order to determine which of the interventions yields a greater level of benefits in relation to the resources invested. Given that a variety of adaptations and development interventions is considered, it is indeed essential to know which of these are the most resource-efficient and cost-effective in producing high benefits for the people.
Based on the findings of CBA, we can determine which adaptation should be dropped, improved and scaled up in favor of other more effective and beneficial interventions. Figure 1 illustrates the analytical framework of the adaptation assessment that is followed in this study. It shows how the necessary data has collected and adaptation evaluation has carried out to deliver a justifiable outcome and generate policy relevant evidence for flourishing socioeconomic resilience in the LTB. It appears in Figure 1 that, beyond the CBA, the study adopted wage days, purchasing power and opportunity cost analysis that further assist the stakeholder in making effective decisions and supporting the welfare-enhancing policymaking for the farmers.
Three tools such as the internal rate of return (IRR), net present value (NPV) and benefit-cost ratio (BCR) usually used in the CBA to measure the quantitative impacts and benefits of an intervention (WB ; McAllister ).
where CFo ¼ initial investment; CF 1 , CF 2 …, CFn ¼ cash where ÀCo ¼ initial investment; C ¼ cash flow at different time; r ¼ discount rate; and T ¼ time/duration.
where PV b ¼ present value of benefits; and PV c ¼ present value of costs. The PV c is the summation of all costs (total cost, TC) involved with specific adaptation. The formula of TC estimation is then: Similarly, the present value of benefits can be described as a summation of all associated benefits of an adaptation.
The equation for estimating the total benefits is furnished as follows.
Due to the nature of the adaptation options in the LTB and unadoptability of IRR and NPV coupled with the unavailability of required data, the BCR approach is considered in this study for performing CBA exercise. The BCR is a ratio of the present value of the flow of benefits to the present value of the flow of costs of a measure. The BCR signifies the overall value for money. If it is greater  For the welfare measurement of the farmers, sellers, and society of the LTB, the following equation has been estimated.
Here, RP f denotes the reservation price of the farmers; and AP f indicates the actual payment made by the farmers.
Here, RP s is the reservation price of the sellers and AP s is the actual payment received by the sellers. It is also worthy to look over the situation of social welfare along with the farmers' and sellers' welfare. This will enable us to reveal and appraise how much welfare the adaptation options are adding to society.
Further, in order to inspect the time benefit of adaptation, the number of wage days enjoyed has been estimated in response to a specific adaptation.
No: of wage days enjoyed ¼ TR cp DW sw (9) where TR cp represents the total revenue receipt from a cropping period; and DW sw is daily wage received for the substitute work.

Climate stresses and adaptation practices
The LTB of Bangladesh experiences multifaceted climate stresses in different seasons throughout the year. These climate stresses affect the livelihood sectors including agriculture, fisheries, and livestock in different ways.

Selection of most practiced adaptations for CBA
As presented in Table 1

Appraisal of short duration variety (SDV) rice
To protect the crop from extreme weather events, the farmers of the LTB apply SDV rice during boro cropping period.
The SDV allows farmers to harvest the crop earlier compared to the traditional type of variety. for SDV rice production indicating US$1 investment in this adaptation option produces US$1.7 return to the farmers. If SDV rice is not adopted in the rice production system, the farmers experience an economic loss of US$370 per ha.  welfare. If other things remain unchanged, the rise in the sellers' welfare will cut the farmers' welfare and vice versa.
In other words, a 10% decrease in the price level of SDV rice causes to escalate the farmers' welfare by 10% keeping the social welfare level constant. In the case of SDV rice, farmers' welfare is exceedingly higher than the sellers' welfare indicating the SDV rice is a highly farmer-friendly and an economically gainful adaptation option which has a considerable impact on farmers' socio-economic resilience to climate change.

Appraisal of alternate cropping (maize)
Alternative crops often have considerable prospect to emerge as a gainful adaptation option over the traditional crop practices. Farmers can enjoy a comparative advantage by adopting alternate crop cultivation in a certain ecosystem. In the LTB, maize was found as one of the most promising adaptations in the sandy and char land. As an alternative crop to rice, maize is popular and vastly   It is found from the CBA in Table 2  Maize produces substantial welfare for the farmers and little for the sellers.    Hence, the total welfare is US$40 which entirely goes to the farmer's level. If the price was negotiated between farmers and BADC, then BADC may have the opportunity to generate some welfare. In the present system, welfare is only concentrated on the farmers. If BADC attempts to maximize its welfare, the farmers need to sacrifice their welfare level. As the government provides subsidies to the BADC for the irrigation service, the irrigation scheme has no objective for profit generation, therefore, farmers can maximize their welfare and receive irrigation at a truncated cost.
In the LTB, the existence of a few co-operative society (CS) based DTWs can be found in different parts that are running through direct participation of the farmers. The member of the CS is responsible for the maintenance and management of the DTW. The member farmers usually get irrigation facilities at a cheaper price which is found lower than the price of BADC in most cases.

Appraisal of shallow tube-well based irrigation
The easy installation and mobility feature allow the shallow tube-well (STW) to use in any type of land in the LTB. Farming of the char land in sandy soil requires more irrigation than the normal land in loamy soil which leads to increased production costs. Table 3

Adaptation decision support matrix
The adaptation decision support matrix (ADSM) explained by Table 4 shows the financially and economically feasibility of adaptation practices. It is also worth mentioning, that the total production expenditure and the contribution of adaptation costs are much higher for STW-based irrigation in sandy/char land which is estimated at US$520 per ha.
While the lowest share of adaptation cost is found for SDV rice which at only US$7.2 per ha. The share of adaptation cost appears less than US$100 for maize cultivation,

Beyond the cost-benefit analysis
In this section, net revenue from the adaptation is assessed from other perspectives of economics such as purchasing power, equivalent wage days, unearned days and opportunity cost. Table 5 demonstrates the number of wage days,   practice presents an additional 97 earning days which estimated opportunity gain is US$349.
The STW-based irrigation (sandy char land) offers comparatively highest opportunity cost for the farmers which is more than double that of other adaptation options.
Likewise, the lowest opportunity cost is found for SDV rice among the adaptation practices which is equivalent to US$50. It is evident that maize as alternate cropping generates opportunity benefit equivalent to US$349 per ha assuring the optimum gain to the farmers which helps