Assessing Flood Risk with ArcGIS Pro

Introduction

River floods represent the most frequent and expensive natural disaster affecting most of the countries around the world . They take place when the river exceeds its storage capacity and the water excess overflows the banks and fills the adjacent low-lying lands, producing significant social, economic, and environmental impacts including: loss of human life and negative effects on population, damage to the infrastructure and essential services, damage to crops and animals, spread of diseases, and contamination of the water supply. Many factors contribute to river floods: heavy rains at river sources, ice jams, the melting of snow pack, and land-use change (such as deforestation and urbanization) are some important factors. Runoff after heavy precipitation is the principal reason for river floods, and as urbanization increases, impervious areas increase as well, leading to higher rates of runoff. Saturated soils, high suspended matter, and landslides also increase the negative impacts of floods.

A. Importance of Flood Risk Assessment

Flooding can have devastating impacts on communities, economies, and ecosystems. Assessing flood risk involves understanding where floods are likely to happen and how severe they might be. This knowledge helps in planning and preparedness, ensuring that people and infrastructure are safeguarded. After all, being proactive can save lives and reduce property damage

B. Overview of ArcGIS Pro

ArcGIS Pro is an advanced geographic information system (GIS) software developed by Esri. Its user-friendly interface allows professionals to create, analyze, and share spatial data effectively. For flood risk assessment, ArcGIS Pro provides powerful tools and data visualization capabilities that can help address the complexities of flood planning.

II. Understanding Flood Risk

A. Definition of Flood Risk

Flood risk refers to the likelihood of flooding occurring in a specific area and the potential consequences it may bring. It takes into account both the probability of various types of floods and the vulnerability of people and property.

B. Types of Floods

Floods can come in various forms that affect different areas differently. The main types include:

• River Floods: When rivers overflow their banks due to heavy rains or melting snow.

• Coastal Floods: Caused by storm surges or high tides along coastlines.

• Flash Floods: Sudden and intense floods that can occur within minutes from heavy rainfall.

C. Factors Influencing Flood Risk

Several factors contribute to flood risk, including:

• Topography: The landscape's features can affect water flow. For example, valleys may collect water, while hills can divert it.

• Weather Patterns: Climate change and seasonal variations influence rainfall and storm occurrences, complicating flood risk assessments.

• Land Use: Urban areas with impermeable surfaces can increase runoff, leading to higher flood risks.

III. Getting Started with ArcGIS Pro

Step 1: Data Collection and Preparation

• Land Use/Land Cover (LULC): Gather data that shows how land is utilized or covered (e.g., urban areas, forests, water bodies, agriculture). This can be sourced from satellite imagery or LULC classification datasets.

• Drainage Density: Obtain stream network data (rivers, creeks, etc.) and calculate the density of drainage features in a specific area. This can be derived from topographic maps, stream networks, or hydrological datasets.

• Distance from Roads: Road network data (shapefiles or feature classes) to calculate the proximity of various locations to roads. This is essential for understanding the potential for infrastructure damage or traffic disruptions during floods.

• Distance from Rivers: Gather river boundary or waterbody data (e.g., shapefiles of rivers) to calculate distances from rivers, which are vital in determining flood risk in areas that may be affected by river overflows.

• Slope: Use a Digital Elevation Model (DEM) to calculate the slope of the terrain. This data shows the steepness of land surfaces, which influences water runoff and potential flood zones.

• Rainfall: Obtain rainfall data from https://crudata.uea.ac.uk/cru/data/hrg/.

• Elevation: Use the DEM to extract elevation data, which will help identify low-lying areas that are more susceptible to flooding, especially in river valleys and floodplains.

Step 2: Preprocessing and Reclassification

Before performing the flood risk analysis, ensure all data layers are compatible and properly formatted:

• Reclassify the Data: Convert each dataset (LULC, distance from roads, rivers, slope, etc.) into a raster format and reclassify the values to represent the contribution of each parameter to flood risk. For example:

  • LULC: Assign higher values to urban areas and impervious surfaces, as they increase runoff.

• Distance from Roads: Assign higher values to areas closer to roads, as they are often impacted by road-related flooding.

• Distance from Rivers: Areas close to rivers should have higher values indicating greater flood risk.

• Slope: Assign higher values to flatter areas, as they are more prone to water accumulation and flooding.

• Rainfall: Higher values for areas with higher rainfall intensity, indicating more potential for flooding.

• Elevation: Assign higher values to lower elevations that are more likely to be flooded.

• Normalize the Data: Standardize all layers to a common scale (e.g., 0-1 or 0-100) so that the different parameters can be compared and weighted equally during the analysis.

Step 3: Assign Weights to Each Parameter

Each parameter has a different impact on the flood risk assessment. Assign a weight to each parameter based on its relative importance to flood risk. For example:

• LULC: 10%

• Drainage Density: 15%

• Distance from Road: 5%

• Distance from River: 20 %

• Slope: 10%

• Rainfall: 25%

• Elevation: 15%

The total weight should equal 100%. The weights can be adjusted based on your understanding of how each parameter influences flood risk in the specific region you are studying.

Step 4: Perform Weighted Overlay Analysis

ArcGIS Pro provides a Weighted Overlay tool to combine these reclassified and weighted parameters. Follow these steps:

• Input Layers: Load all the pre -processed, reclassified raster layers into the Weighted Overlay tool.

• Set Weighting: Assign the weight values for each layer in the tool’s settings.

• Execute the Analysis: Run the tool to combine all the layers. The result will be a new raster layer where areas of higher flood risk are represented by higher values.

Step 5: Flood Risk Mapping and Classification

After performing the weighted overlay analysis, you will obtain a raster layer representing flood risk. The next steps include:

• Map Visualization: Visualize the resulting flood risk layer in ArcGIS Pro. Areas with higher risk will have higher values (e.g., red for high risk, yellow for moderate risk, green for low risk).

• Classify the Results: Classify the flood risk values into risk zones (e.g., low, medium, high) to make the results more understandable and actionable.

• Create Flood Risk Map: Customize your map to display key features like flood risk zones, road networks, and rivers. This map can be used for decision-making, urban planning, and flood mitigation strategies.

Step 6: Evaluate Vulnerability and Exposure

Once the flood risk zones have been mapped, you need to evaluate the vulnerability and exposure of the population, infrastructure, and critical assets to the identified flood risks.

• Vulnerability: Assess the resilience of buildings, roads, and infrastructure in flood-prone areas. Areas with more critical infrastructure or high population density near flood zones should be considered high priority for flood mitigation measures.

• Exposure: Analyze the level of exposure based on the flood risk zones and the population or infrastructure located within them. You can use demographic data or infrastructure layers (e.g., hospitals, schools) to assess exposure.

Conclusion

In conclusion, ArcGIS Pro is an essential tool for conducting comprehensive flood risk assessments. By integrating and analyzing multiple datasets—such as Land Use/Land Cover (LULC), drainage density, distance from critical infrastructure, slope, rainfall, and elevation—this approach enables a detailed understanding of flood-prone areas. The use of Weighted Overlay Analysis provides an effective method to combine these variables, allowing for the identification of areas with varying levels of flood risk.

Through this assessment, communities and decision-makers can better understand the potential impacts of river, coastal, and flash floods. By identifying high-risk zones, evaluating the vulnerability and exposure of infrastructure and populations, and visualizing flood risk through detailed maps, ArcGIS Pro supports informed decision-making in urban planning, disaster preparedness, and flood mitigation strategies.

Ultimately, this approach contributes to improved flood resilience, safeguarding lives, property, and critical infrastructure from the devastating effects of flooding. It empowers authorities to take proactive measures to manage flood risks effectively, reduce potential damage, and protect communities.