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Introduction to Spatial Introduction to Spatial CalculationCalculation
Estimation of Areas Estimation of Areas Susceptible to Flood and Susceptible to Flood and
Soil LossSoil Loss
Estimation of Areas Estimation of Areas Susceptible to Flood and Susceptible to Flood and
Soil LossSoil Loss
Spatial CalculationsSpatial Calculations
• Integrating multiple layers of information– Susceptibility to flood– Vulnerability to soil loss
– Other examples:• Land cover change (e.g., deforestation,
agricultural / urban expansion)
Areas Susceptible to FloodsAreas Susceptible to Floods
• Selection of certain DEM characteristics– Spatial Analyst / Extraction / Extract by
Attributes
• Selection of a river buffer zone– Analysis Tools / Proximity / Buffer
Coastal Areas Susceptible to FloodsCoastal Areas Susceptible to Floods
• Use DEMs at different resolutions to select the cells with low values
Inland Areas Susceptible to FloodsInland Areas Susceptible to Floods
• Use rivers to define areas susceptible to inland flooding– By buffer zones– With pixels with the same elevation as
the rivers
– Include: past floods / historic events
Vulnerability to Soil LossVulnerability to Soil Loss
• Prepare and combine (multiply) various layers of information– Slope
• Directly obtainable from a DEM
– Soil erodability (k-factor)• Depends on soil type and texture• Inherent soil characteristics
– Rain erosivity (factor-r)• Obtained from annual precipitation and
elevation• Impact of rain’s characteristics on soil
Vulnerability to Soil Loss (1)Vulnerability to Soil Loss (1)
• DEM Slope in degrees– Verify the degree range
• Definitions of soil types and textures– Various sources, but K-factor is needed
to explain soil erodability– Frequently, soil data is presented with
vectors
Vulnerability to Soil Loss (2)Vulnerability to Soil Loss (2)
• Rain erosivity (R-factor) is a calculation expressed by equations derived for different areas in terms of annual precipitation and elevation
Vulnerability to Soil Loss (3)Vulnerability to Soil Loss (3)
• Vulnerability to soil loss spatial expression is a multiplication of:– Slope– K-factor (soil erodability)– R-factor (rain erosivity)
• More or less weight can be given to different factors, according to the circumstances of the area of interest
Vulnerability to Soil Loss (4)Vulnerability to Soil Loss (4)
x x
Summarize and apply these resultsSummarize and apply these results
• How do we summarize this information?
• Application:– Susceptibility to natural disasters– Land degradation
Summarize the resultsSummarize the results
• Why do we use the basin as a unit of measurement?
?
How to present the resultsHow to present the results
Generating summary Generating summary reports for geo-spatial reports for geo-spatial
datadata
Generating summary Generating summary reports for geo-spatial reports for geo-spatial
datadata
Summary JustificationSummary Justification
• For whom or why summarize?• What to summarize? – results
generated or obtained• Where to summarize? –think spatially• How to summarize? – the tools
For whom or why summarize?For whom or why summarize?
• Other investigators, decision makers, politicians, students, the public
• A raster does not always present the conclusion desired
• The conclusions have to matter to the audience
¿Summarize what?¿Summarize what?
– Land cover / land use– Flow accumulation– Areas susceptible to floods– Soil loss vulnerability– Susceptibility to natural disasters
¿Where to Summarize?¿Where to Summarize?
• Summarize rasters by area of interest– Points
• Pour point• City
– Lines• Rivers• Roads
– Polygons• Watersheds• Municipalities
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Use Surface (ha)
Surface (%)
FA
LS
E B
AS
IN
Primary forest
600 7.50
Secondary forest
400 5.00
Scrub Shrub
6000 75.0
Bare soil 200 2.50
Pasture 200 2.50
Urban 100 1.25
Agriculture 500 6.25
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Fuente: CATHALAC 2008
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Source: Atlas, SINAPROC
What and Where?What and Where?
Land cover / Land use
LineLine Gallery forest
PolygonPolygonCover by basin or province
Flow accumulation
PointPointDischarge point
Flood susceptible areas
PointPoint City
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Vulnerability to soil loss
LineLineSusceptible roads
PolygonPolygonSusceptibility by municipality
Source: Atlas, SINAPROC
How to Summarize?How to Summarize?
• Tools– Extract Values to Points
– Zonal Statistics
– Tabulate Area
Discharge PointsDischarge Points
• Summarize flow accumulation in a list of discharge points– Extract values to point– Not only useful for flow accumulation, but also
for any other result related to water, sediment, and nutrient/pollutant transport
Percentage of Forest CoverPercentage of Forest Cover
• Calculate the forest cover percentage inside each watershed– Tabulate Area– Discrete data– Join this table to the spatial data through a
shared ID
Vulnerability to Soil LossVulnerability to Soil Loss
• Summarize the vulnerability by watershed, or inside any polygon– Continuous data– Zonal statistics
Vulnerability to Soil LossVulnerability to Soil Loss
• Other uses for Zonal Statistics– Municipal population estimates – Others?
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