Developing a multivariable lookup table function for estimating flood damages of rice crop in Vietnam using a secondary research approach

It is increasingly important to evaluate the economic flood damage toward agricultural crops to further improve decision-making and mitigate flood impacts in developing countries. In this study, we derive a multivariable lookup table function for estimating flood damages to rice crops based on a secondary research approach, which involves collecting and integrating fragmented secondary information sources of rice damage caused by inundation and event data observed in southern rural areas of the Ca River Basin, Central Vietnam. The derived lookup table function includes the effects of the rice growth stages on the damage caused, in addition to flooding parameters such as inundation level and inundation duration. This indicates that the rice crops are generally the most vulnerable and robust to inundation in the ripening and the reproductive stages. The yield loss in the ripening stage dramatically increases from 50% to 90% when the complete inundation lasts 5 to 8 days. Even after 7 days of 75% inundation, the yield hardly decreased at the reproductive stage and was reduced by almost half for 7 days of complete inundation. Four-five days of complete inundation at the ripening and vegetation stages are likely to cause almost the same damage to rice crops as that caused by 7 days of inundation at the reproductive stage. Utilization of the function to estimate rice damage in four flood events reveals that the derived multivariable function captures flood damages well and outperforms the univariable damage functions for the target area.