Sea-level rise vulnerability mapping using LiDAR DEMs

Global sea-level rise SLR is projected to accelerate over the next century, with research
indicating that global mean sea level may rise 18–48 cm by 2050, and 50–140 cm by 2100.
Decision-makers, faced with the problem of adapting to SLR, utilize elevation data to identify
assets that are vulnerable to inundation. This paper reviews techniques and challenges stemming
from the use of Light Detection and Ranging LiDAR Digital Elevation Models DEMs in support
of SLR decision-making. A significant shortcoming in the methodology is the lack of
comprehensive standards for estimating LiDAR error, which causes inconsistent and sometimes
misleading calculations of uncertainty. Workers typically aim to reduce uncertainty by analyzing
the difference between LiDAR error and the target SLR chosen for decision-making. The
practice of mapping vulnerability to SLR is based on the assumption that LiDAR errors follow a
normal distribution with zero bias, which is intermittently violated. Approaches to correcting
discrepancies between vertical reference systems for land and tidal datums may incorporate tidal
benchmarks and a vertical datum transformation tool provided by the National Ocean Service
VDatum. Mapping a minimum statistically significant SLR increment of 32 cm is difficult to
achieve based on current LiDAR and VDatum errors. LiDAR DEMs derived from ‘ground’
returns are essential, yet LiDAR providers may fail to remove returns over vegetated areas
successfully. LiDAR DEMs integrated into a GIS can be used to identify areas that are
vulnerable to direct marine inundation and groundwater inundation reduced drainage coupled
with higher water tables. Spatial analysis can identify potentially vulnerable ecosystems as well
as developed assets. A standardized mapping uncertainty needs to be developed given that SLR
vulnerability mapping requires absolute precision for use as a decision-making tool.