BNPP/ASB Functional Value of Biodiversity Project – Phase II 

Sensitivity of river systems to forest cover change: a pan-tropical perspective.

b. Proposed figures and tables:
1. map of potential vs current land cover
2. “matryushka” plot (DQ vs Area)
3. example(s) of change in hydrograph
4. example(s) of change in frequency/return periods.
5. map of population exposed to DQ
6. table of datasets
7. table of DQ at selected return periods
8. table of populations at risk

a. Premises:
1. LUCC results in DQ
2. Impacts are spatially complex but policy makers require practical decision tools
3. Typologies have been used successfully to generalize geophysical attributes globally
a. Maybeck et al: mountain typology
b. Green et al: nitrogen transport

b. Approach:
1. Meine develops “rules of thumb” based on virtual watershed simulations.
2. UNH applies “rules” to the pan-tropics to develop pan-tropical typology.
3. Summarize by typology the sensitivity to LUCC w.r.t. changes in floods, low flows, total yield.

Kate Sebastian, Stanley Wood, Ellen Douglas and Charles Vorosmarty

The pan-tropical component of the FVOB study is predicated on the existence of significant tracts of tropical forest that simultaneously provide havens of biodiversity richness as well as socially beneficial watershed services. The study seeks to identify the location and extent of such tracts and generate evidence of the nature and scale of the watershed services they provide. This new knowledge will help assess the scope for targeting and prioritizing watershed conservation efforts that would, by design, provide significant spillover benefits in terms of biodiversity conservation. Put another way, the strategy recognizes and capitalizes upon the relative political efficacy of justifying investments in watershed protection rather than in biodiversity protection per se.

The FVOB study builds on, and seeks to test, a number of key hypotheses and assumptions . Micro and meso level data and models are being used to characterize relationships between climatology and streamflow response. By juxtaposing various spatial and temporal scales of climatology with various spatial scales and patterns of land cover change, this work is establishing “rules of thumb” for predicting local hydrological responses to land cover change that can be applied across the tropics. Another thrust is in assessing the potential “far field” threats to downstream human settlements posed by land cover changes occurring in upstream forest areas. A key element in assessing the likely dynamics of either local or far field effects is the definition of relevant land use change scenarios. This paper describes a set of land use change scenarios designed to generate information of relevance to addressing the central questions of the pan-tropic study: Where are remaining tracts of tropical forest? To what extent have biodiversity and hydrological function already been impacted by deforestation? Where are the most important and most threatened areas of biodiversity in remaining forest tracts? What would be the benefit, and to whom, of maintaining the existing hydrological function in such areas?

Four scenarios are described. The first scenario attempts to reconstruct the change in land cover that has taken place since pre-industrial times. The second and third lay the basis for assessing the potential magnitude of the hydrological consequences of conserving (a) currently threatened forest areas, and (b) the most biodiversity-rich forested areas. The fourth scenario attempts to calibrate the most likely rate and location of actual land cover change on the basis of current projections of agricultural expansion to 2015.

Several issues, some unresolved, have surfaced during the course of this (on-going) effort. First, many incompatibilities exist between the vegetation classification schema of global datasets on ecoregions (potential or climax vegetation) and land cover (actual vegetation) that limit analytical options in defining the first (pre-industrial to current) scenario. Second, the qualitative and often subjective steps necessary to generate globally applicable measures of biodiversity and conservation often make it difficult to “unbundle” such measures into component parts that might provide greater flexibility in defining scenarios. Third, use of any specific hydrological model brings its own set of opportunities and constraints. It is non-trivial to triangulate and arbitrate amongst the limits imposed by the spatial and temporal resolution of available data, the limits imposed by the spatial and temporal intervals over which the hydrological and hydraulic analytical routines are valid, and the need for impact-relevant information that resonates with policymakers. Finally, projections about likely expansion of the agricultural frontier are speculative at best, and will be influenced by factors ranging from the impact of WTO negotiations on regional patterns of comparative advantage, the role of technology and improved practices in raising land productivity, and the emergence of innovative production opportunities such as biofuels and other bioengineered industrial crops that bring new deforestation pressures. See Figures 4 and 5. 

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