HYDROLOGICAL IMPACTS OF LANDUSE CHANGE IN THE HILLSIDES OF

COLOMBIA : THE IMPACT OFPATTERN ON PROCESS

Mark Mulligan* and Jorge Rubiano†* Department of Geography, King’s College London, Strand, LONDON, WC2R 2LS.

mark.mulligan@kcl.ac.uk† Hillsides Agroecosystems Project, CIAT, A.A. 6713, Cali, Colombia

The HERB project

• Hydrology, Ecology and Regional Biodiversity of tropicalMontane forest

• Collaborators : CIAT, Instituto “Alexander von Humboldt”(Min. Env.), University of Cauca, Fundacion ProSelva

• Two scales of working (a) experimental catchments (25mres.) (b) Colombia-wide (1 Km res.)

• Concerted research efforts:• 1995-1996 - Rio Ñambi, Nariño, Colombia• 1997-present - Reserva Tambito, Cauca, Colombia

The Tambito Experimental Catchments• 1374-2894 masl, 5.5 by 4.1 Km , 1424 Ha.

– 861 Ha. Primary, 527 Ha. Secondary and 36 Ha. Pasture (1996).

• Paired Catchments– of Palo Verde (Primary) and Tambito (Secondary and Pasture).

Slopes, altitudes, soils and geologies similar.

• GIS Data :– 25m DEM, historic land use data (LANDSAT TM,1989 and

manual survey,1996)

• Monitoring network:– 3 hydrological/meteorological plots– 7 tipping bucket raingauges throughout catchment– various throughfall, stemflow, occult precipitation and soil erosion

traps– 100s of soil and litter samples from throughout catchment

Tambito, Colombia

Top left Temperatureandhumidity probe atforest site

Top right Pasture andresearch facilities

Bottom left Installing thestemflow apparatus

Bottom right The pasturehydrological station

AREA DESCRIPTION

- 3.400 Ha

- Area ranging between 1200 - 2200 MASL

- Population 5000.

- 2 Ha per family.

LAND COVER 1946, 1970 AND 1994

Historical Land Use Change in Tambito1996 manual floristic survey (Alex Cortes, Univ. Cauca)

A Simple Cellular Model for Land UseChange at the Agricultural Frontier

• Models conversion of forest to pasture only• Requires only DEM, original land use, roads and rivers• Assumes that conversion spreads out from:

– (a) rivers– (b) roads– (c) agricultural frontiers

• Also assumes that the resistance to spread α sin(slope)• Does not model rate of deforestation just form.• Applicable to mountain environments at the agriculture-

forest frontier without complex patterns of ownership.• Replicates but simplifies observed pattern of change

Rate of deforestation is initially high but slows as (a) theagricultural frontier shrinks and (b) the shallow slopes areconverted leaving only steeper slopes

0

200

400

600

800

1000

1200

1400

1600

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49

Timesteps

Area

(Ha) Deforested (Ha)

Secondary (Ha)Primary (Ha)

The graph is a plan view of a series of frequency histogramsfor slope angles of land under pasture for timesteps from1..50. Early in the series the frequency distributions arebiased towards low slope angles.

0 8 16 24 32 40 48 56 64 72 80 88

S1

S5

S9

S13

S17

S21

S25

S29

S33

S37

S41

S45

S49

frequency (fractional)

slope angle (degrees)

Timestep

0.08-0.090.07-0.080.06-0.070.05-0.060.04-0.050.03-0.040.02-0.030.01-0.020-0.01

The graph is a plan view of a series of frequency histogramsfor elevations of land under pasture for timesteps from 1..50.

Early and late in the series the frequency distributions arebiased towards low elevations.

1300

1475

1650

1825

2000

2175

2350

2525

2700

2875

S1S5S9S13S17S21S25S29S33S37S41S45

Frequency (fractional)

Altitude (m)

Timesteps

0.125-0.15

0.1-0.125

0.075-0.1

0.05-0.075

0.025-0.05

0-0.025

Modelling the HydrologicalImpact

• Dynamic GISmodel built using PCRASTER• Spatially distributed

– rainfall, solar, net and PAR radiation– land cover parameters– soil texture, thickness and bulk density

• Processes– interception– infiltration and overland flow, routed downslope– soil evaporation, transpiration, interception loss– recharge, throughflow, soil moisture– plant growth and partitioning– soil erosion

– See Mulligan and Rubiano (forthcoming)

Hydrological Patterns

Total evapotranspiration (mm/hr), effective rainfall (mm/hr),runoff (mm/hr) and soil moisture (m3water/m3soil) for 1400

hrs 22nd January 1998.

Experiment

• Take each of the 50 iterations of the LUCmodel as a land use scenario

• Run the hydro model for the same month ofmeteorological data (January 1998) for eachof the land use scenarios

• Compare the hydrological behaviour of thecatchment for each of the land use scenarios

PATTERNS - soil moisture

Iteration 3, for 1400 hrs 22ndJanuary 1998.

Iteration 16, for 1400 hrs22nd January 1998.

How is the PATTERN of change important?

• Evapo-transpiration, recharge and soil moisture0

5

10

15

20

25

30

350 10 20 30 40 50

Iteration of land use change

Sen

sitiv

ity (c

hang

e in

out

put f

lux

per u

nit c

hang

e in

la

nd u

se) e

vap

and

rech

arge

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Sen

sitiv

ity (c

hang

e in

out

put f

lux

per u

nit c

hang

e in

la

nd u

se) e

vap

and

rech

arge

soi

l moi

stur

e

Total catchment rechargeTotal catchment evapotranspirationMean catchment soil moisture

How is the PATTERN of change important?

• Runoff and soil erosion

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25 30 35 40 45iteration of land use change

Sen

sitiv

ity (c

hang

e in

out

put f

lux

per u

nit c

hang

e in

land

use

)

Sum erosionSum runoff

Hydrological Projects

• Mauricio Rincon-Romero - Modelling LandscapeSensitivity to Land Use Change

• Jorge Rubiano - Hydrological Impact of Land Use Change: a cellular model based on RS data

• Andrew Jarvis - Monitoring and Modelling OccultPrecipitation at the Plot Scale

• Juliana Gonzalez - Monitoring and Modelling OccultPrecipitation at the Catchment Scale