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Climate Change Risk and Adaptation Assessment for Irrigation in Southern Viet Nam: Water Efficiency Improvement in Drought-Affected Provinces (December 2020)

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Executive Summary

This report presents the results and findings of the climate risk and adaptation assessment (CRA) of the Water Efficiency Improvement in Drought-Affected Provinces (WEIDAP) project in Viet Nam. The assessment was done during the project preparation phase, with an individual consultant from the United Kingdom (UK) Met Office supporting the technical assistance (TA) team.

The CRA adopted good practices from the Asian Development Bank (ADB) Climate Risk Management Framework (ADB 2015a, 2016b) and international guidelines (e.g., EUFIWACC 2016), particularly in considering a wide range of possible climate futures and potential risks over the lifetime of the proposed investment. The TA team was thus able to take stock of climate adapation activities that were already part of the project, as well as to refine the team’s recommendations. Those same practices also informed the detailed design of the project and the monitoring of progress in implementing climate adaptation measures.

This report was prepared to capture lessons learned from the CRA for the WEIDAP project and new developments in climate risk assessment that are relevant to ADB operations and future risk assessment projects. These lessons and new developments are highlighted throughout the report with cross-references to other ADB reports or external resources.

Climate Risk and Adaptation Assessment for the Water Efficiency Improvement in Drought-Affected Provinces Project

The WEIDAP project is expected to improve water productivity in irrigated agriculture by replacing inefficient rice irrigation schemes with modernized systems using pipes (pressurized and gravity), upgraded canals, and impounding weirs designed for irrigating high-value crops, such as mango, coffee, pepper, and dragon fruit. The improvement is to be achieved through institutional and capacitybuilding activities (component 1), modernized irrigation schemes (component 2), and enhancements in on-farm water efficiency (component 3).

The 2015–2016 drought influenced by the El Niño–Southern Oscillation affected around 60,000 hectares of agricultural land in the Central Highlands, including the main area of coffee production, as well as 20%–30% of the areas growing rubber, pepper, cashew, and tea (ADB 2017a). The global assessments of hydrological droughts indicate an increase in the frequency of dry conditions in southern Viet Nam since the 1950s (e.g., Beguería et al. 2013). Rainfall during the southwest monsoon period was 40%–70% below the long-term average in the five target provinces, as shown in the analysis done for the CRA.

Future climate change scenarios project an increase in annual average rainfall within the region (MONRE 2016), but a delayed start and reductions in rainfall in the monsoon season cannot be ruled out. If the full range of published climate change scenarios is considered, there are plausible scenarios that indicate a reduction in rainfall during the monsoon period (Katzfey, McGregor, and Suppiah 2014).

The Fifth Assessment Report of the Intergovernmental Panel on Climate Change states that El Niño– Southern Oscillation-related precipitation variability on a regional scale is likely to intensify with increased moisture availability (van Oldenborgh et al. 2013). More recent research published in Nature (Cai et al. 2015) suggests that the frequency of El Niño conditions may increase twofold by the end of the century. The assessment of Coupled Model Intercomparison Project 5 (CMIP5) models for this project shows that dry periods may occur more frequently even when there is an increase in annual average rainfall.

The CRA used climate change scenarios from the Ministry of Natural Resources and Environment (MONRE 2016) and several supporting research projects. Twenty-five future climate projections for the 2050s, covering medium- and high-emission scenarios, were reviewed. Rather than adopting a multi-model median or average scenario, the CRA used a climate-futures approach (Whetton et al. 2012) in translating these into three simple scenarios for analysis:

• Scenario 1 is a warm-and-wet scenario under lower emissions, with warming of just over 1ºC in the coastal provinces and a significant increase in average annual river flow and groundwater recharge.

• Scenario 2 is a hot-and-wet scenario under high emissions, with warming of 1.5ºC in the highland provinces and almost 2ºC in the coastal provinces. Similar changes in annual rainfall occur, but the increased evaporation translates into smaller increases in river flow and recharge than under scenario 1.

• Scenario 3 is a hotter scenario under high emissions, with a warming of 2ºC in the highland provinces and 2.6ºC in the coastal provinces. It has a drier start to the southwest monsoon season and is likely to have a delayed onset in drier years. Flow and groundwater recharge decrease under this scenario.

From the perspective of climate vulnerability and the ability of communities to cope with drought conditions, the target areas have poverty rates of 15%–30% but also include some wealthier farming communities. Overall, these areas have relatively low vulnerability compared with surrounding areas; Dak Nong and Ninh Thuan, however, have a higher proportion of people living in poverty and rank lowest on the Human Development Index.

The climate risk assessment considered potential impact based on the three climate scenarios, using a mixture of hydrological modeling, literature review, and expert elicitation within the TA team. A range of biophysical, agricultural, and infrastructure risks, such as increase in evaporation, higher crop water demand, change in river flows and crop yield, and damage to project infrastructure due to flooding, was included. All scenarios presented increased risks of flooding and sea-level rise. The hotter scenario posed risks of both increased flooding and more frequent drought conditions.

Economic analysis to test subproject economic rates of return under climate change, with and without the WEIDAP project, was also carried out. It indicated the likelihood of high returns from the project even under the most severe hotter climate scenario. The highest risk to the project investment comes from a succession of severe droughts, particularly at the start of the project, and from extreme flooding and damage to newly built infrastructure. The impact on farmer incomes would be significant but will still be improved with the project under the more extreme climate scenarios.

Asian Development Bank: © Asian Development Bank