Since this is the quantitative part of a larger report describing the Vietnamese natural hazard environment, its main constraint is the availability of data. If a hazard or an impact channel cannot be described quantitatively, it cannot be analyzed here, but will still be discussed in the main report. For several relevant assets exposed to natural hazards, no official catalogues of geolocated assets exist or could be found. To still provide estimates of hazard exposure where possible, this work assembles some datasets from openly available sources. While these datasets should not be regarded as complete, they provide the best possible estimates, and hopefully as such are useful to policymakers.

In locating assets affected by hazards, data compiled from satellite imagery is especially important. Rather than simply using the raw output from the sensor, this analysis combines multiple types of such data and algorithmically detects specific objects, such as aquaculture ponds or rice paddies. While no such datasets were created originally for this analysis, several developed in other contexts were applied here. The employment of such datasets opens analyses of hazards at spatial granularities and geographic ranges that were not possible before, covering very large areas at very fine resolutions.

Sections two and three of this paper describe the hazard and sectoral data employed in the analyses, respectively. Section four details the methodology through which exposure estimates were computed for all relevant hazard/sector combination. Section five describes an approach to approximate the impact of such exposure in economic terms. Section six finally discusses the methodologies employed and concludes.

# 2. Hazard data

This analysis quantitatively considers four types of natural hazards affecting coastal Vietnam: flooding, typhoon winds, coastal erosion, and drought and saline intrusion. These hazards were selected based on discussions with experts and insights from existing literature describing the risk landscape in Vietnam (Rentschler et. al 2020, chapter 3). In this section, the data employed to model each hazard are described.

## 2.1. Flooding

This analysis uses one dataset modelling fluvial and pluvial flooding and a second one modelling coastal flooding. For sake of simplicity the combination of fluvial and pluvial flooding is addressed as riverine flooding in the main report. Fluvial flooding occurs when excessive rainfall over an extended period of time causes a river to exceed its capacity. A pluvial, or surface water flood, is caused when heavy rainfall creates a flood event independent of an overflowing water body. A coastal flood occurs in areas that lie on the coast of a sea, ocean, or other large body of open water, and is typically the result of extreme tidal conditions caused by severe weather (World Meteorological Organization, 2011).

The first dataset combines information on flood extent and flood depth from pluvial and fluvial flooding into one flood map. It was developed by the company Fathom, formerly known as SSBN. The map covers all of Vietnam at a resolution of about 90 by 90 meters. Flood events with return periods of 5, 20, 50, 100, 250, and 500 years are modelled. A 100-year event, for example, is expected to occur once every 100 years, on average (figure 2.1.a). As with most large-scale flood maps, the effects of man-made flood protection structures like dikes are not incorporated. The dataset is in raster format (Bangalore et al. 2017).

Existing coastal flood maps covering Vietnam, most prominently the Global Tide and Surge Reanalysis (GTSR) data set (Muis et al. 2016), are expected to underestimate coastal flood risk in Vietnam. Resulting from coarse resolution in modelling elevation, bathymetry and meteorological forcing, the dataset underestimates extreme sea levels. In addition, the largest tropical cyclone-induced surges are not all 4