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De Graff et al., 2011


Recognizing the importance of tropical forests in limiting rainfall-induced debris flows

De Graff, J.V., Sidle, R.C., Ahmad, R. Scatena, F.N. (2011)
Environmental Earth Science  


Worldwide concern for continuing loss of
montane forest cover in the tropics usually focuses on
adverse ecological consequences. Less recognized, but
equally important to inhabitants of these affected regions, is
an increasing susceptibility to rainfall-induced debris flows
and their associated impacts. The same high rainfall rates
that sustain tropical forest cover can often serve as the
triggering mechanism for debris flows. The natural rate of
debris flow occurrence on steep slopes subject to episodic,
intense rainfall is dependent on the stabilizing effect of
tropical forests. Either loss or significant reduction in forest
cover can weaken this natural defense. Information from
postdisaster observations and research on the November
1988 storm event in southern Thailand provides a case
study illustrating the potential impacts of increased debris
flow susceptibility resulting from conversion of forest cover
to rubber tree crops. Development resulting in the loss of
tropical forest cover may be accompanied by local increase
in population, property development, and infrastructure.
Consequently, the potentially disastrous consequences of
increased debris flow occurrence are amplified by the
greater vulnerability of local populations. Preserving the
tropical forest cover is an obvious and often difficult means
of retaining this natural protection. Effective policy should
capitalize on the values of tropical forests as part of the
strategy for retaining adequate forest cover. Policy should
also seek to avoid creating pressures that foster forest
removal or their conversion to other types of land cover in
steep terrain. Areas where tropical forests were converted to
other cover types can be restored to secondary forests to
avoid a permanent state of increased debris flow susceptibility.
Restoration of secondary tropical forests can successfully
re-establish the forest characteristics that limit
debris flow occurrence. Experience in Central America and
the Caribbean demonstrates that successful restoration is
possible but requires a significant commitment of both time
and resources. In addition to the cost and technical difficulties
involved, the increased susceptibility to debris flow
occurrence persists through many years until successful
restoration is achieved. Both retention of existing tropical
forests and restoration of forest cover where loss has
occurred are often justified by the reduced risk of debris
flow impacts to vulnerable populations and infrastructure.


De Graff, J.V., Sidle, R.C., Ahmad, R. Scatena, F.N. (2011): Recognizing the importance of tropical forests in limiting rainfall-induced debris flows. Environmental Earth Science. DOI: 10.1007/s12665-012-1580-8