Spatial 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 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 Floods

•  Use DEMs at different resolutions to select the cells with low values

Inland 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 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)

•  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)

•  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 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)

x x

Summarize and apply these results

•  How do we summarize this information? •  Application:

– Susceptibility to natural disasters – Land degradation

Summarize the results

•  Why do we use the basin as a unit of measurement?

?

Summary 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?

•  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?

– Land cover / land use – Flow accumulation – Areas susceptible to floods – Soil loss vulnerability – Susceptibility to natural disasters

¿Where to Summarize?

•  Summarize rasters by area of interest – Points

•  Pour point •  City

– Lines •  Rivers •  Roads

– Polygons •  Watersheds •  Municipalities

What and Where?

Land cover / Land use

Gallery forest

Cover by basin or province

Flow accumulation Discharge point

Flood susceptible areas

City

Susceptible roads Susceptibility by municipality

Vulnerability to soil loss

Susceptible roads Susceptibility by municipality

What and Where?

Land cover / Land use

Gallery forest

Cover by basin or province

Flow accumulation Discharge point

Flood susceptible areas

City

Susceptible roads Susceptibility by municipality

Vulnerability to soil loss

Susceptible roads Susceptibility by municipality

Use Surface (ha)

Surface (%)

FALS

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?

Land cover / Land use

Gallery forest

Cover by basin or province

Flow accumulation Discharge point

Flood susceptible areas

City

Susceptible roads Susceptibility by municipality

Vulnerability to soil loss

Susceptible roads Susceptibility by municipality

What and Where?

Land cover / Land use

Gallery forest

Cover by basin or province

Flow accumulation Discharge point

Flood susceptible areas

City

Susceptible roads Susceptibility by municipality

Vulnerability to soil loss

Susceptible roads Susceptibility by municipality

Source: Atlas, SINAPROC

What and Where?

Land cover / Land use

Gallery forest

Cover by basin or province

Flow accumulation Discharge point

Flood susceptible areas

City

Susceptible roads Susceptibility by municipality

Vulnerability to soil loss

Susceptible roads Susceptibility by municipality Source: Atlas, SINAPROC

How to Summarize?

•  Tools – Extract Values to Points

– Zonal Statistics

– Tabulate Area

Discharge 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 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 Loss

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

Vulnerability to Soil Loss

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