LAUSR

Abstract The rationale for mapping hydrological risks in the Mekong River Delta (MRD) is the large extent of flood-affected and salinity-affected areas that severely constrain rice production. This new study on risk mapping expands previous approaches in depth (resolutions of 300 × 300 m and 1 h) and width (combining different types of maps). Data obtained with a hydrological model have been evaluated through four different methods of mapping individual attributes of risks that collectively comprise a comprehensive risk assessment for rice production: 1) Peak risk maps: These maps show the maximum water heights in a high-water year and maximum salinity concentrations in a low-water year. 2) Time-sequenced risk maps: The article provides hyperlinks to videos that encompass time-sequenced maps for the critical periods of floods (July-December in daily intervals) and salinity (March-April in hourly intervals) for all provinces. 3) Sustained risk maps (for rice): This approach is based on clearly defined thresholds of flood and salinity risks considering the duration of risk exposure at a given location. We have set thresholds for water heights exceeding 0.4 m and salinity concentrations above 2 g/l for 7 consecutive days to define start and end dates of sustained risks for rice. 4) Risk profile maps (for rice): The data on sustained risk have been aggregated at province level to calculate the geographic coverage of risk areas as compared with the total rice area. The rice area exposed to sustained flood risks in the MRD comprises 39% of the total rice area, which can be further subdivided into 24% with long (>three months), 12% with moderate (1–3 months), and 3% with short (1–4 weeks) risk duration. Likewise, the salinity-prone rice area accounts for 44% of the total rice area and can be subdivided into 31% with long, 8% with medium, and 5% with short risk duration. Finally, we have discussed the pros and cons of these different risk mapping methods in view of required adaptation strategies for rice production to cope with rapidly changing environmental conditions.