Activity 2. Scale of effects of land cover change on watershed
functions in the humid tropics
Terms of Reference
Introduction / context
This activity concerns the spatial scale of areas where watershed functions are at risk due
to land use change (viz, risk of flooding, diminished base flow in areas of rising demand,
sedimentation of reservoirs, etc) and the coincidence of these ‘hydrological hotspots' with
areas where biodiversity richness is at risk due to land use change (biodiversity 'hotspots')
and human poverty in the humid tropics.
Undisturbed forest can be a source of clean water and of biodiversity, so the two tend to
be associated with each other in a broad sweep across the globe. Yet, there is no direct
functional link between the two. In a few percent of area in the tropics, ‘cloud forest’
does contribute to streamflows, but even this physical effect does not depend on a highly
diverse natural vegetation.
Efforts to protect forest lands from ‘human disturbance’ can as a side effect maintain
clean water flows, but natural forests/highly biodiverse systems are not unique in
providing this service, and the value appears to be overrated in much of the public debate,
despite the efforts of researchers (notably Hamilton, Bruijnzeel and Calder) to expose the
myths involved. The global review of ‘forests, water, people’ relations undertaken in
2000 (by Bonell et al) has marshalled evidence from around the world that
traditional/general public perceptions of ‘forest watershed functions’ need revision.
Current process-based understanding of the hydrological cycle leaves doubts regarding
the meso-scale (10 – 1000 km) impacts on rainfall distribution of large-scale forest
clearing, but otherwise leads to a separation of tree effects (intercepting/using more
water than other vegetation), soil effects (maintaining infiltration rates) and landscape
integrity (esp. filter functions in riparian strips). Once decomposed in these terms, one
can better understand the impacts land use change in the forest margin can have on
properties such as total water yield of a catchment, partitioning between peakflow and
baseflow, sediment load and the buffer capacity for extreme rainfall episodes. None of
these subsets of ‘watershed functions’ is logically dependent on forest biodiversity per se.
Despite the apparent lack of functional relationships, there may nevertheless be
significant scope for fiscal relationships between biodiversity conservation and watershed
functions. It is difficult to charge local and national groups the full costs of
conservation of global environmental services -- viz, existence values and conservation of
endemic species. Indeed, local/national populations should not be expected to pay the
full costs of conservation of globally important biodiversity, nor is it desirable (or even
feasible) to impose these costs on them. Moreover, it is not even clear that it is feasible
either to generate sufficient funds globally to compensate local people for the opportunity
costs or to create institutions that can effectively transfer the payments (even if the money
were available).
Although watersheds – like biodiversity conservation hotspots -- suffer from externalities
/ free rider problems and other market failures associated with public goods and services,
the scale of the problem is (sometimes) smaller, making it easier to imagine feasible
fiscal or other mechanisms within conventional administrative boundaries (or between
adjacent nations) to compensate 'winners' and 'losers' of policies to address the
externalities.
In some areas, by virtue of climate and topography, the biodiversity conservation
problem and the watershed problem may coincide. Among ASB sites, for example, this
may obtain in Montane Mainland Southeast Asia and some of the islands of Indonesia
and the Philippines. In cases where the problems coincide spatially (and in scale), then
feasible fiscal and other mechanisms for addressing the (bundle of) watershed problems
also may be able to produce biodiversity conservation as a side effect. In other areas -where there is a misfit between the location and/or scale of the problems, the market
failures and inappropriate incentives for conservation may need to be tackled separately
for conservation of watersheds and for biodiversity.
Goal(s) / research hypothesis
Process-based hydrological models are necessary to move ahead in our understanding of
hydrology and its policy implications. But the question remains: at what scale are these
relevant to watershed (or biodiversity conservation) policy? Discussion at a 1999 ASB
workshop in Chiang Mai suggested that better understanding of the scale of policyrelevant watershed functions is in our grasp -- this is the goal of this activity. If the
influence of land cover change on watershed functions attentuate within 1-10 km, then
there would seem to be no point in attempting to model those functions at the pantropic
scale – since resolution of data available at present are not sufficient. Even if sufficiently
detailed data were available, it is not clear this would be a productive approach.
Certainly, for the micro scale / case study level (see Activity 5), this sort of modelling
may make sense. The big area of doubt is the meso-scale -- is it useful and feasible for
the Mekong for example? (Participants at that workshop also suggested that a similar
understanding of the scale of biodiversity conservation problems is not readily available,
at least not by Dec 2002. That is why this project mainly will rely on secondary sources
of 'biodiversity hotspots'.)
Hypothesis for Activity 2. Except for water quality, effects of conversion of natural forest
to agriculture on hydrological processes and other watershed functions attenuate within 10
km. (NB: scale of effects will have to be examined for specific functions).
Tasks
A key assumption of this activity is that individuals with specialized expertise are willing to
collaborate. The activity leader, in consultation with leaders of other activities, will
identify and seek involvement from key collaborators with experience in tropical hydrology
and spatial analysis.
Through consultation among collaborators, experts will synthesize knowledge (and identify
gaps) on the effect of land cover change on hydrological processes and other watershed
functions at different scales in the humid tropics. At what scale is land use / cover
change relevant for watershed functions? Best reviews of evidence available will be
identified on what links (if any) there are between land cover change (deforestation) and
risks of flooding, water shortage, and deterioration of water quality (including siltation).
Experts will collaborate with policy analysts to produce a brief policy-oriented synthesis
of existing information for the humid tropics. The crucial strategic question from a
policy perspective is to identify the scale of the transition from meso-level effects that are
strongly influenced by land cover and macro phenomena where land cover has little
influence.
Insights regarding scale of effects will be applied to pantropic spatial analysis (building on
Activity 1) to identify ‘hydrological hotspots’. How do watershed hotspots relate spatially
to human populations and biodiversity ‘hotspots’?
The activity leader will facilitate interaction by various expert collaborators by email in
preparation of draft outputs.
Once drafts are available, the activity leader will organize a meeting of collaborators to
review and finalize written outputs. (Funds budgeted for this meeting may be used for
more than one meeting or for individual consultancies, or some combination of these
options, at the discretion of the activity leader in consultation with the global coordinator
and the World Bank project manager.)
Results will be published in forms appropriate for researchers and for policymakers;
results also will contribute to Activity 2 and to ASB global publications.
Deliverables
2.a. Summary and synthesis of knowledge on hydrological processes at different scales in
the humid tropics, including review of literature, with indication of knowledge gaps and
research implications (if any) for this project.
2.b. Draft paper specifying ‘rules of thumb’ and data requirements for identifying-- at
pantropic, meso, and local levels --areas where hydrological functions are sensitive to
land cover change, ie., ’hydrological hot spots’.
2.c. Draft policy brief with context-specific recommendations about the scale at which
the effects of land cover change on hydrological functions attenuate.
2.d. Hydrological hot spots map at pantropic scale (based on watershed maps and DEM
from Activity 1) and scale of watershed units determined above in 2.b and 2.c.
2.e. Documentation and analysis of spatial distribution of hydrological hot spots (2.d),
biodiversity hotspots and human population (from Activity 1). The project will then try
to determine: How many people live in such areas? How poor are they? What is the
local and global significance of the biodiversity in these areas? What downslope areas
benefit from flood prevention – and who lives there, and how poor are they?
2.f. Meeting of experts to finalize paper (2.b) and policy brief (2.c) and to assess research
and policy implications of spatial analysis with hydrological hot spots (2.d. and 2.e).
Schedule: Work will begin in April 2001 and will culminate in a meeting of experts to
finalize drafts of written deliverables by the end of March 2002. (Outputs are needed in
early 2002 as inputs for Activities 3, 4, and 5.)
Team members (CVs attached)
Meine van Noordwijk (leader)
Thomas P. Tomich
Ken Chomitz
Stan Wood
Budget (by calendar semester, Jan- June; July-Dec)
Line item
2001 / I
2001 / II
Research personnel
8665
8665
Meeting
Other costs
300
500
Subtotal
8965
9165
Total: USD 84429
2002 / I
20299
45500
500
66299
2002 / II
0