International Expert Meeting on Forests and Water, November 20-25, 2002, Laforêt Biwako, Japan

Tropical Forests and Water :

The UNESCO International Hydrological Programme

Perspective

Mike Bonell,

Chief of Section Hydrological Processes and Climate, UNESCO Division of Water Sciences, Paris, France

World map showing the distribution of the three climatic sub-types (humid, subhumid, wet-dry) of the humid tropics. Also shown is the dry tropical region.

Tropic of Cancer

Tropic of Capricorn

TROPICAL CLIMATE

H

HUMIDSUBHUMIDWET-DRYDRYHIGHLANDS

COLDEST ISOTHERM MONTHS (18°C)

After Chang & Lau, 1993

Report from the joint UNESCO/IUFRO International Symposium:

Forests-Water-People in the Humid Tropics:

Past, Present and Future Hydrological Research

for Integrated Land and Water Management

30th July to 4th August 2000

Bangi, Kuala Lumpur, Malaysia

Hosted by the Universiti Kebangsaan Malaysia

Forests-Water-People in the Humid Tropics,Cambridge University Press (Editors: M. Bonell & S.

Bruijnzeel), to be published in late 2003.

Section 1: Current trends and perspectives on people/land use/water issues

⇒ Trends and patterns of tropical land use change

⇒ Policy responses in South East Asia river basins

⇒ Land-use change in the Brazilian Amazon: resource manager’s perspective

⇒ Tropical forest, people-changing land in South East Asia

⇒ The economics of tropical countries: biophysical and economic efficiency linked with forest

⇒ Community-based hydrological and water quality assessments in Mindanao, Philippines

⇒ People in tropical forests: problem or solution?

⇒ Politics of the link between forests and water in Central America

⇒ Land use, hydrological function and economic valuation

Section 2: Hydrological processes in undisturbed forest

⇒Meteorology and climatology of the humid tropics

⇒ Rain producing systems in the humid tropics

⇒ Climate variability

⇒ Evaporation

⇒ Runoff generation

⇒ Erosion and sediment yield

⇒Mineral nutrition

⇒ Tropical montane cloud forest

Section 3: Impacts on forests : disturbance, conversion and recovery

⇒ Impacts of natural disturbances

⇒Water, nutrient and sediment flows in selective forestry operations

⇒ Effects of shifting cultivation and forest fire

⇒ Soil and water impacts during forest transformation and stabilisation to new land use

⇒ Large-scale hydrological impacts of tropical forest conversion (Amazonbasin)

⇒ Secondary forest recovery

⇒ Hydrological impacts of reforestation of grasslands and of degraded forest

⇒ Agroforestry for sustainable land-water management

Section 4: New methods for evaluating effects of land-use change

⇒ Remote sensing tools

⇒ Detecting change (trends) in river flow series

⇒ Surface runoff modelling in gauged and ungauged catchments: an example from northern Thailand

⇒ How to choose an appropriate catchment model

⇒ Isotope tracers in catchment hydrology

⇒ Tropical stream ecology methodologies

⇒ Process-based erosion modelling

⇒ How to achieve a water balance of tropical wetland (swamp) forest

Section 5: Critical appraisals of best management practices

⇒ Controlling catchment impacts from timber harvesting: a global perspective

⇒ Forest management and catchment services: a Malaysian perspective

⇒ Guidelines for forest clearing operations

⇒ Soil and water management for rainfed steeplands

Concluding chapter

⇒ A synthesis of the key issues ⇒⇒⇒

Over-Arching Issues Emerging from the Book

Governance▪ Strong “top-down” “command and control” approach

▪ Current institutional weakness involving community participation

▪ Importance of community participation in forest management and technical projects

▪ Political expediency by governments through the use of myths (e.g. sedimentation in dams)

There has been effective transfer of existing scientific knowledge from drainage basin research into the formulation of guidelines

▪ Use of research findings from humid temperate and humid tropical experimental basins

▪ Concept of “Red Flag” (sensitive) areas: tropical montane cloud forests, riparian buffer zones, unstable slip prone zones, etc.

▪ More concentration on land husbandry methods (e.g. agroforestry) for soil conservation

▪ Optimal engineering solutions already exists (terracing)

General Biophysical Issues

Climatic Variability Impacts:

▪ Inherent variability (ENSO, Sahalian, Decadal, Multidecadal) linked with High/Low Flows, Fire, Tropical Cyclone Frequency.

Terrestrial-Climate Interactions:▪ Scale effects

▪ Feedbacks (e.g. biogeophysical (surface albedo), hydrological (changes in transpiration))

▪ Emergent properties in GCMs for runoff changes

⇒ results for runoff changes from large-scale field simulations using GCMs not being aliged with small-scale controlled experiments

⇒ precipitation re-cycling/reorganisation of spatial and temporal occurrence of rainfall

1111

(After Lean et al. 1996)

Hadley Centre GCM prediction of change in rainfall following imposed whole-scale deforestation to pasture in Amazonia

1 0.5 0 -0.5 -1 -1.5

Change in rainfall (mm per day)

1212

IMPACT OF LAND USE: CHANGE ON MESOSCALE RAINFALLIMPACT OF LAND USE: CHANGE ON MESOSCALE RAINFALL

Figure: A mesoscale model simulation of clouds at 21 GMT on 15 May 1991 over part of the USA. Left: the model simulation with current landscape and right: using the natural landscape, showing a significant impact on the development of clouds resulting from a change in land cover type (adapted from Pielke et al, 1997)

After Pielke et al., 1997

General Biophysical Issues (2)

Extreme Events:

▪ Lack of process hydrology data during extreme events

▪ Lack of short-term rainfall data

▪ Need for coupling rainfields movement with runoff processes

HURRICANE MITCH: SATELLITE-DERIVED , SPATIAL 3-DAY RAINFALL TOTALS, OCT. 29-31 1998HURRICANE MITCH: SATELLITE-DERIVED , SPATIAL 3-DAY RAINFALL TOTALS, OCT. 29-31 1998

10N

12N

14N

16N

18N

20N

94W 92W 90W 88W 86W 84W 82W 80W

25 25 100 150 200 250 350 400 500 600 700 800

After Ferraro et al., 1999

Figure:Total rainfall accumulation (mm) for the 3-day period of October 29-31, 1998, using the GOES Multispectral rain algorithm (GMSRA) technique

MAXIMUM RAINFALL: HURRICANE MITCH, ATLANTIC AND GLOBAL EVENTSMAXIMUM RAINFALL: HURRICANE MITCH, ATLANTIC AND GLOBAL EVENTS

Figure: Plot of maximum rainfall amounts (squares) against duration from a rain gauge in Southern Honduras during hurricane/tropical storm Mitch (y=51.64x0.674, R2=0.99). Also plotted are updated record rainfall events (diamonds) for different durations1,2 that define the curve of maximum potential rainfall (y=353.07x0.519, R2=0.99) and data (triangles) from recent major Atlantic hurricanes and tropical storms3-5

10,000

1,000

1000

10

10.01 0.10 1 10 100 1,000

Record Mitch Atlantic

Duration (hours)Duration (hours)

Prec

ipita

tion

(mm

)

After Hellin, Haigh & Marks, 1999

1616

MARVEX

Location of MARVEX (MahurangiRiver Variability Experiement)

Plate 2. Radar rainfall data over the Mahurangi catchment (a) rainfall every two minutes from 0200h to 0300h (local time) on 11 August, 1998; (b) five 1-hour rainfall averages and a 5-hour average map, from 2200h August 10 to 0300h August 11. The river network is over-plotted on the first image for scale. Images are labelled with the time at the end of the averaging period.

1717

Plate 3. Runoff data for the Mahurangi catchment: five 1-hour average maps and a 5-hour average map, from 2300h August 10 to 0400h August 11. Images are labelledwith the time at the end of the averaging period.

After R. Woods et al, 2001

General Biophysical Issues (3)

Need for more a Process-orientated, Integrated Approach which combines Hydrology Sediment and Nutrient Transfer and Freshwater Ecology studies:

▪ Limited number of process-orientated case studies across the humid tropics, viz:

- evaporation

- runoff generation

- groundwater (v. poor representation)

- freshwater ecology (v. poor representation)

- biogeochemical cycling (v. poor representation below surface)

THE SPECTRUM OF KNOWN AND INFERRED HYDROLOGIC FLOWPATHS IN TROPICAL RAINFOREST SOILSCAPES

THE SPECTRUM OF KNOWN AND INFERRED HYDROLOGIC FLOWPATHS IN TROPICAL RAINFOREST SOILSCAPES

After Elsenbeer, 1999

“Acrisol”End-Member

“Ferralsol”End-Member

Bukit Soeharto, Bukit Tarek, Reserva Ducke

La Cuenca, KianiLestari, Mendolong,South Creek

Danum, Rancho Grande

Specific Biophysical Issues

The use of simpler, parametrically-parsimonious conceptual models (PPCMs) as alternatives to heavily parameterised, distributed models:

▪ The scale issue (point v. hillslope v. subdrainagebasin)

▪ Concept of emergent properties

▪ The inadequacies of existing techniques biased to point measurements

2121

2222

15%

20%

25%

30%

35%

40%

45%

50%

Wet and dry states of soil water distribution

Spring period in southern Australia -strong topographic control

WET

14%

16%

18%

20%

22%

24%

26%

0 100

Summer period in southern Australia -little topographic control

DRY

Figure 8. Example of the dry state soil water distribution measured at the Tarrawarra catchment (each cell represents one measurement). Soil water content in % vol./vol. Flume is marked at catchment outlet.

2323

MARVEXWET DRY

Plate 4. Measured soil moisture patterns at the Satellite station catchment for (a) August 1998 and (b) February 1999, also showing the location of CS615s and transects.

2424

RA

INFA

LL (m

m/h

)

HYD

RA

ULI

C H

EAD

(m) φ

= ψ

−Ζ

Julian Day, 1991

T15 T30 T45 T60 T90 T120

CM

Tensiometers NC4

NB. SHADED AREAS DENOTE SATURATION

2525

Example of diffusion dominated soil water pressure waves

Fig. 4. Soil water pressure heads from tensiometer readings in unsaturated saprolite, Column 3, resulting from periodic irrigation at the column surface.

2626

Fig 3. In situ soil-water retention curve data. The identification numbers correspond to the shaded locations of Figure 1. The wetting curves are black dots, and the drainage curves have open triangles. Experiments at nest 2-1 experienced instrument failure.

CONCEPTUAL BABINDA MODELQUASI NON-LINEAR STORAGECONCEPTUAL BABINDA MODELQUASI NON-LINEAR STORAGE

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P ♠ EFFECTIVE PRECIPITATION

UPPER STORE QUICKFLOW RECESSION (Saturation α1 TIME CONSTANT ~1.3hOverland flow,Shallow sub-surface stormflow, ≤ 0 .2 m d e p th )

g PARTITIONING COEFFICIENT ~0.87h

α2

SLOW

FASTTHRESHOLD STORAGE H1

WELL MIXED DEEP GROUNDWATER

H1

H2 > 3000 mm

THRESHOLD STORAGE OF DEEP GROUND WATER REQUIRED TO SUSTAIN NEAR-CONSTANT BACKGROUND ISOTOPIC CONCENTRATIONS IN BETWEEN STORMS

MIXING LAYER OF VARIABLE THICKNESS JUST BELOW WATER TABLE OF PREFERENTAL INPUTS THROUGH UNSATURATED ZONE

LOWER STORE(Deeper 'unsaturated' Zone Sub-surface stormflow, plus Groundwater)

SLOWFLOW RECESSION TIME CONSTANT ~52h

AVAILABLE WATER STORAGECAPACITY~12mm

P

FRACTURED BEDROCK

PERMANENT GROUNDWATER

STREAM

SATURATION OVERLAND FLOW

SUBSURFACE STORMFLOW (PERCHED WATER TABLE)

PERCOLATION

IMPEDING LAYER

CONCEPTUAL CATCHMENT MODELDURING MONSOON STORMSCONCEPTUAL CATCHMENT MODELDURING MONSOON STORMS

After Bonell & Barnes, 2000

Specific Biophysical Issues (2)

Riparian and Hyporheic Zones:▪ Sparse information on the hydrological and biogeochemical transfer functioning of riparian zones

▪ More research needed on the function and buffer strip protection of riparian zones during forest operations

Sparse information on the Role and Function of Tree Roots:▪ Applications in reforestation-afforestation, agroforestry, GCMs (e.g. Amazon)

▪ Evaporation

▪ Nutrient cycling

RIPARIAN ZONESRIPARIAN ZONES

Lack of detailed hillslope hydrology studies on connectivity between riparian zones with hillslopes:

Water balance study of Lørup (1998) Southern Tanzanian highlands catchments (4.48 to 5.16 km²)

Rio IcacosDemonstrates surface-

groundwater linkage and estimate of Ks along 100m

reach

3131

Riparian wells

Sampling sites for whole-reach enrichmentHyporheic well groupings

Tracer injection point for whole-reach enrichment

Figure 1. Map of puerto Rico showing locations of the study sites in the Luquillo Experimental Forest

Figure 1. A.- Topographic map of 100-m study reach along a tributary of the Rio Icacos. Scale = 1:350, topographic contour interval = 25 cm, elevation change upstream to downstream = 50 cm. Bold arrow indicates direction of stream flow. B.- Groundwater flownet for the study. Scale = 1:350, water table contour interval = 20 cm. Streamlines showing the direction of groundwater flow are represented by arrows.

New Tools:

▪ Environmental Tracers for Isotope storm Hydrograph Separations

▪ New tools for application in swamp forests

▪ Statistical approaches for detecting trends (changes) in longer term rainfall and runoff data sets (global change)

▪ Remote sensing

North Creek

South Creek

North CreekSouth Creek

Q‘old’ water

Q‘old’ water

30

20

10

0

30

20

10

0

1.00.80.60.40.2

047.0 47.2 47.4 47.6 48.0 48.2 48.4

47.8

Old

Wat

er

Frac

tion

Stre

amflo

w(m

m/h

)St

ream

flow

(mm

/h)

Julian Day, 1991

CHEMOHYDROGRAPH SEPARATIONSCHEMOHYDROGRAPH SEPARATIONS

After Bonell et al., 1998

Concluding Points

Need for Long-Term Monitoring and Research:

▪ Surprising lack of new research literature since 1980s concerning controlled experimental studies linking the various hydrological impacts (total water yield, stormflow, baseflow) with forest management guidelines e.g. RIL (Reduced Impact Logging, this book provides an example):

- needs to be linked with climate variability impacts and more comprehensive process-orientated studies.

▪ Incompatibility of temporal scales in the development of economic policy (using short time scales) vis-à-vis hydrological monitoring needs (long time scales) (many examples of site-specific policy-making without any hydrological data)

▪ Critical absence of firm technical data on the impacts of afforestation-reforestation of degraded catchments :

- Land Use Change, Watershed Services and Socio-Economic Impacts in the Western Ghats, FORD Fondation/UNESCO IHP Funded –Centre for Interdisciplinary Studies in Environment and Development, Ashoka, Trust for Research in Ecology and the Environment, NIH (India), Karnataka Forest Dept.

Conflict Between Sustainable Development vis-à-vis Sustainable Development:

▪ Many writers infer the consequences of imposing the western economic model on developing countries (Govts, Donors, int. corporate enterprises, export-orientated activities) (i.e. does neo-classical economics provide an excuse to plunder !)

▪ Is there an alternative biophysical economic approach ?

- More focus on increasing economic outputs for less energy or material impacts

- Integration of forest governance and participatory management

- More realistic position on available biophysical resources and economic possibilities to ensure basic needs (forests, clean water) available to populace

- Escalation in population needs to be addressed

Pan-Tropical Demonstration / HELP Basins

▪ societal acceptance of best management practices

To deliver social, economic and environmental benefit to stakeholders through sustainable and appropriate use of water by directing hydrological

science towards improved integrated catchment management basins

Hydrology for the Environment, Life and Policy

HTTP://WWW.UNESCO.ORG/WATER/IHP/HELP

Real people Real catchments Real answers

“Paradigm Lock ”

Isolated by legal and professional precedence

……based on outdated knowledge and technology

Process hydrology Water managers and stakeholders

ideasresearch

understanding implementation

outputdesign

Isolated by lack ofproven utility

Acceptedpractices

Isolated by dissagregated institutions

HELP PILOT PHASE DRAINAGE BASINS

Africa1. Olifants (South Africa,

Mozambique)2. Thukela (South Africa)

North and Central America17. Lake Ontario (USA, Canada)18. Red-Arkansas/Little Washita (USA)19. San Pedro (USA, Mexico)20. Luquillo Mountains (Puerto Rico)21. Panama Canal (Panama)22. Yakima (Washington, USA)23. Hudson (NY &NJ, USA)

Australasia3. Motueka (New Zealand)4. Mount Lofty (Australia)5. Murrumbidgee, sub-basin of Murray Darling (Australia)

Asia6. NE of Thailand and Vietnamese Delta, sub-basins of Mekong (6 countries in Asia)7. Subernarekha (India)8. Yasu or Tama (Japan)9. Aral Sea (Central Asia) 10. Walawe (Sri Lanka)11. Tarim (China)

Europe12. Herault ( France)13. Danube (5 countries in Europe)14. Spree-Havel (Germany)15. Upper Severn (UK)16. Thames (UK)

Middle East (None)

South America24. Rio Jau and/or Rio Branco

or Ji-parana (Brazil)25. Rio Jequetepeque (Peru)

ν 17ν 18

ν 19

λ 21

σ22σ23

λ 24λ 25

λ 13σ14

λ 15

λ 16

λ 1λ 2

ν 3

ν 425

λ 6

λ 7

λ 9

λ 10

λ 11

2 Reference HELP Basinν Operational HELP Basinλ Evolving HELP Basinσ Proposed HELP Basin

λ 12

σ20

σ 8

HELP PILOT PHASE DRAINAGE BASINS

Africa1. Olifants (South Africa,

Mozambique)2. Thukela (South Africa)

North and Central America17. Lake Ontario (USA, Canada)18. Red-Arkansas/Little Washita (USA)19. San Pedro (USA, Mexico)20. Luquillo Mountains (Puerto Rico)21. Panama Canal (Panama)22. Yakima (Washington, USA)23. Hudson (NY &NJ, USA)

Australasia3. Motueka (New Zealand)4. Mount Lofty (Australia)5. Murrumbidgee, sub-basin of Murray Darling (Australia)

Asia6. NE of Thailand and Vietnamese Delta, sub-basins of Mekong (6 countries in Asia)7. Subernarekha (India)8. Yasu or Tama (Japan)9. Aral Sea (Central Asia) 10. Walawe (Sri Lanka)11. Tarim (China)

Europe12. Herault ( France)13. Danube (5 countries in Europe)14. Spree-Havel (Germany)15. Upper Severn (UK)16. Thames (UK)

Middle East (None)

South America24. Rio Jau and/or Rio Branco

or Ji-parana (Brazil)25. Rio Jequetepeque (Peru)

ν 17ν 18

ν 19

λ 21

σ22 σ23

λ 24λ 25

λ 13σ14

λ 15

λ 16

λ 1λ 2

ν 3

ν 425

λ 6

λ 7

λ 9

λ 10

λ 11

2 Reference HELP Basinν Operational HELP Basinλ Evolving HELP Basinσ Proposed HELP Basin

λ 12

σ20

σ 8