From Principles to Numbers: Approaches in Implementing Payments for Environmental Services (PES) in the Philippines - Smallholder Tree Growing for Rural Development and Environmental Services - page 368

may not necessarily lead to biodiversity conservation. In addition, there are pitfalls
in using the deductive approach (i.e., applying general principles to species cases).
For instance, the indiscriminate planting of trees in watershed areas could actually
lead to increased evapo-transpiration, resulting in a reduction in the total water
flowing out of the watershed (Farley et al. 2005; Jackson et al. 2005). This has
already been observed in some watersheds in the Philippines (Cruz et al. 2005).
Finally, another weakness of the Tier 1 approach is that attribution is not clear. In
other words, it is not clear whether an environmental service has indeed been deliv-
ered based on the actions taken. This returns to the problem of the lack of quantita-
tive measurements currently available for the environmental services being
provided.

17.2.2 Tier 2: Use of Simulation Modeling and Limited

Site-Specific Data

Under the Tier 2 approach, simulation modeling and limited site-specific data are
used to quantify the flow of environmental services expected. This assumes that a
minimum data set is available to parameterize models developed in other locations.
Below we present two cases to illustrate the use of this approach.

17.2.2.1 Case 1: Bakun Watershed, Benguet

Bakun municipality and its watershed is located in the northwestern part of Benguet
province. It is about 86 km north of Baguio City. The centre of the watershed is
located on 120°40 N latitude.

The Bakun watershed is the source of domestic water supply for the local com-
munity. More importantly, it is the source of irrigation water for the rice fields and
expanding vegetable farms in the area and the operation of two hydroelectric power
plants.
A Rapid Hydrological Assessment (RHA) was conducted to develop an effec-
tive, fair and transparent environmental transfer mechanism as well as to find an
acceptable method of determining the extent to which the quantity and quality of
water delivered to downstream users can be attributed to the management efforts of
the upland communities. The hydrological functions of the watershed were assessed
using three knowledge domains as the framework, namely, the scientific ecological
knowledge using quantitative hydrologic methods, local ecological knowledge and
the public ecological knowledge. Additionally, the GenRiver hydrologic model 2
was used to estimate the streamflows and related hydrologic processes.

′ 48 ″ E longitude and 14°48 ′ 00 ″

2 A model developed by the ICRAF for hydrologic assessment.