Nimpact Academy - Module 12: Human Impact Assessment

Quantifying Human Footprint from Space

Natural environmental factors (temperature, vegetation, erosion) tell only part of the story. Human activities—development, urbanization, lighting—profoundly impact coastal ecosystems. Nimpact uses satellite sensors to measure these anthropogenic pressures.

Why Human Impact Matters for Beaches

Development increases runoff → More sediment, pollutants, and nutrients entering water
Impervious surfaces alter hydrology → Reduced infiltration, increased peak flows during storms
Light pollution disrupts ecosystems → Affects nesting sea turtles, migratory birds, nocturnal species
Urbanization indicates pressure → More visitors, potential for pollution and habitat loss

The Four Human Impact Metrics

Night Lights Intensity: Direct measure of human activity and development density
Urban Development Index (NDBI): Tracks built-up area expansion over 20+ years
Development Pressure Score: Combines multiple indicators into single risk metric
Land Surface Temperature: Shows urban heat island effect and land use changes

Metric 1: Night Lights Analysis

Nimpact uses VIIRS (Visible Infrared Imaging Radiometer Suite) data from NOAA satellites to measure nighttime radiance—a proven proxy for human activity, economic development, and population density.

# Night Lights Data Source
Satellite: NOAA-20 VIIRS Day/Night Band
Dataset: VIIRS DNB Monthly Composites
Resolution: 500 meters
Coverage: 2021-2024 (monthly averages)
Measurement: Average radiance (nW/cm²/sr)

# Processing Method
1. Filter to 500m buffer around beach
2. Calculate mean radiance across 36+ months
3. Classify intensity level
4. Compare to regional benchmarks

Night Lights Classification

Radiance Range	Classification	Interpretation
< 5 nW/cm²/sr	Remote/Dark	Minimal human presence—wilderness, protected areas
5-15	Low Development	Rural areas, small communities, low-density recreation
15-40	Moderate Development	Suburban areas, medium towns, active development
40-80	Urban	Cities, commercial districts, high population density
> 80	Dense Urban	City centers, industrial areas, maximum development

McGregor West Example:

Mean Radiance: 0.52 nW/cm²/sr
Classification: Remote/Dark

Interpretation: This is a remote location with minimal light pollution—excellent for stargazing, natural habitat preservation, and minimal anthropogenic disturbance. The low value (< 1) indicates virtually no nearby urban development.

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Metric 2: Urban Development Index (NDBI)

The Normalized Difference Built-up Index (NDBI) uses shortwave infrared and near-infrared bands to distinguish built structures from vegetation and bare soil.

NDBI Calculation Method

# NDBI Formula (Sentinel-2)
NDBI = (SWIR - NIR) / (SWIR + NIR)
NDBI = (Band11 - Band8) / (Band11 + Band8)

# For Landsat 7/8
NDBI = (Band5 - Band4) / (Band5 + Band4)

Values range from -1 to +1:
  NDBI > 0.2:   Urban/built-up areas
  NDBI 0 to 0.2: Bare soil, sparse development
  NDBI < 0:     Vegetation, water

Why NDBI Works

Built-up areas (concrete, asphalt, roofs) reflect SWIR strongly but absorb NIR → high NDBI

Vegetation reflects NIR strongly but absorbs SWIR → negative NDBI

This creates a clear spectral signature for urbanization!

20-Year Change Analysis

Nimpact compares two periods to track development trends:

Period	Years	Satellite	Purpose
Historical	2000-2009	Landsat 7	Baseline conditions
Recent	2020-2025	Sentinel-2	Current development

Development Pressure Classification

# Change Analysis
NDBI_Change = Recent_NDBI - Historical_NDBI

# Classification Thresholds
Change > 0.10:    HIGH pressure (Rapid development)
Change 0.05-0.10: MODERATE pressure
Change -0.05-0.05: LOW pressure (Stable)
Change < -0.05:   DECLINING (Decreasing development)

Interpreting Development Metrics

NDBI Change	Pressure Level	Environmental Implications
> +0.10	High	Rapid urbanization—expect increased runoff, habitat loss, water quality impacts
+0.05 to +0.10	Moderate	Active development—monitor for cumulative impacts on beach ecosystems
-0.05 to +0.05	Low/Stable	Minimal change—development pressure not a primary concern
< -0.05	Declining	Vegetation recovery or de-urbanization—positive environmental trend

Built Area Percentage

The report also estimates % of land area developed:

# Conversion Formula (calibrated)
Built_Area_% = max(0, min(100, (NDBI + 0.2) × 150))

Example:
  NDBI = -0.10 (mostly vegetation)
  Built% = (-0.10 + 0.2) × 150 = 15%
  
  NDBI = 0.15 (urban area)
  Built% = (0.15 + 0.2) × 150 = 52.5%

⚠️ Critical Context: Water Masking

Nimpact uses JRC Global Surface Water to mask out water pixels before calculating NDBI. This ensures the analysis measures LAND development only—not open water, which would artificially lower NDBI values at coastal sites.

McGregor West Example:
Recent Built Area: 14.7%
NDBI Change: -0.102 (Declining pressure)

Only ~15% of the land area within 500m is developed, and that percentage has actually decreased slightly over 20 years—likely vegetation recovery.

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Metric 3: Development Pressure Index

The Development Pressure Index combines multiple indicators into a single comprehensive score:

Components of Development Pressure:

Night lights intensity (1km buffer)
Night lights trend (5km buffer for regional context)
NDBI change rate
Built area percentage increase
Proximity to urban centers (from population data)

Scoring: 0-100 scale, where higher = greater development pressure

Pressure Score Interpretation

Score Range	Level	Management Implications
0-25	Low	Remote areas—minimal development threat, focus on conservation
25-50	Moderate	Emerging pressure—establish monitoring programs, consider zoning
50-75	High	Active development—implement stormwater BMPs, restrict clearing
75-100	Very High	Urban beaches—require intensive management, restoration programs

McGregor West Example:

Development Pressure Score: 17.1/100
Level: Low
Night Lights (1km): 0.530 nW/cm²/sr
Night Lights (5km): 0.650 nW/cm²/sr

Analysis: Both the immediate area and broader region show minimal lighting, confirming low development pressure. The slightly higher 5km value suggests small rural communities exist in the broader area, but they're not impacting the beach site.

Metric 4: Land Surface Temperature

Landsat's thermal infrared band measures land surface temperature (LST)—the actual temperature of the ground and vegetation, not air temperature.

LST Calculation

# Landsat 8/9 Thermal Band (Band 10)
# Step 1: Convert Digital Numbers to Brightness Temperature
Brightness_Temp_K = DN × 0.00341802 + 149.0

# Step 2: Convert Kelvin to Celsius
LST_°C = Brightness_Temp_K - 273.15

# Analysis Parameters
Period: Summer months (Jun-Sep Northern / Dec-Mar Southern)
Years: 2020-2025
Buffer: 500m around beach

Temperature Classification

LST Range	Class	Typical Land Use
< 18°C	Cool	Water bodies, dense forest, irrigated agriculture
18-23°C	Moderate	Mixed vegetation, grasslands, low-density development
23-28°C	Warm	Bare soil, dry grassland, moderate urban areas
28-35°C	Hot	Urban surfaces, exposed rock, arid lands
> 35°C	Very Hot	Dense urban, industrial, deserts, parking lots

Urban Heat Island Effect

LST is typically 5-10°C higher in developed areas compared to vegetated surroundings. This "heat island effect" results from:

Dark surfaces (asphalt, roofs) absorbing more solar radiation
Reduced evapotranspiration from vegetation loss
Heat from buildings, vehicles, industrial processes
Reduced wind flow in urban canyons

Elevated LST near beaches can stress coastal ecosystems and increase water temperatures through runoff.

Practical Applications

For Beach Managers:

Low pressure sites (< 25) → Prioritize conservation, limit development
Moderate pressure (25-50) → Implement smart growth policies, buffer zones
High pressure (> 50) → Require stormwater treatment, habitat mitigation

For Property Buyers:

Low night lights → Quiet, dark skies, minimal neighbors
Declining NDBI → Neighborhood greening, increasing property values
High LST + high development → Potential for beach water quality issues

Page 3 of 3 - Ready for Quiz

🏙️ Module 12: Human Impact Assessment