introduction to spatial calculation estimation of areas susceptible to flood and soil loss

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


• 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 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


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







Flow accumulation



PointPoint City






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





Flow accumulation



PointPoint City










Flow accumulation



PointPoint City






Fuente: CATHALAC 2008





Flow accumulation



PointPoint City










Flow accumulation



PointPoint City






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


• Summarize the vulnerability by watershed, or inside any polygon– Continuous data– Zonal statistics


• Other uses for Zonal Statistics– Municipal population estimates – Others?

introduction to spatial calculation estimation of areas susceptible to flood and soil loss

Documents

soil lossprepare

soil data

soil erodabilityfrequently

soil loss spatial expression

soil lossother examples

different areas

rain erosivity rfactor

different resolutions