🛠️ Workflow

This document outlines the step-by-step workflow used to project the extent of coastal flooding in Hong Kong in 2100.

Steps

A. 🔩 Data Preparation

• Download Land Utilization Raster Grid, and Hong Kong Digital Terrain Model from DATA.GOV.HK
• Restyle classification symbology for Land Utilization Raster Grid layer
• DTM dataset does not contain any coordinates
  • Manual Georeferencing is required

B. 🗺️ Topographic Map

Run Contour (Spatial Analyst) to convert DTM layer into a topographic map

• As a Python Script:

  import arcpy
  
  # Setting workspace
  arcpy.env.workspace = r"C:\Users\User\Documents\JonathanLeung_Winter2025\HK_DTM_5m_Full"
  arcpy.env.overwriteOutput = True
  
  # Contour Tool
  HK_DTM = "Whole_HK_DTM_5m.asc"
  outContour = r"C:\Users\User\Documents\JonathanLeung_Winter2025\HK_DTM_5m_Full\HK Processing\HK Processing.gdb\Contour_Whole_HKDTM"
  arcpy.sa.Contour(HK_DTM,outContour,contour_interval=30,base_contour=0, z_factor=1,contour_type='CONTOUR') 

C. 📡 Digital Elevation Model

• Set boundary for Topo to Raster (Spatial Analyst)
  • Generate a feature class of polygons covering the entire Hong Kong territory

• Run Topo to Raster (Spatial Analyst) to convert the topographic map to a DEM

D. 💧 Flood Level Simulation

• Run Raster Calculator (Spatial Analyst) to generate binary raster layers that indicate areas that would be submerged under water or not. This project uses these figures for analysis:

Emission Scenario	Median (m)	Algebra Expression
Very low	0.38	"HKDEM" <= 0.38
Intermediate	0.56	"HKDEM" <= 0.56
Very High	0.78	"HKDEM" <= 0.78

Red indicates flooded areas Grey indicates non-flooded areas

• Delete the grey label in the symbology tab for better visualization

E. 🔣 Symbology

• Main Map
  • Apply OpenStreetMap Dark Gray Canvas Base (WGS84) as basemap
  • Overlay flood binary raster layers on top of each other
  • Style all binary raster layers in different shades of blue or cyan

• Inset Maps: highlight 3 specific areas to showcase impact
  • Overlay the intermediate emission scenario flood binary raster layer on Land Utilization Raster Grid
  • Apply transparency and layer blend to show what land use would be affected by coastal flooding

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Final Product