1. The importance of tropical mountains, dams and PWS Schemes
A focus on water productivity in the Andes system of basins
Leonardo Saenz1 and Mark Mulligan2
King’s College London
King’
Payments for Watershed services (PWS) Schemes as soft interventions for a more integral watershed management are proliferating especially in the tropics.
With growing water demands from agricultural, industrial and domestic sectors and increasingly to meet energy needs in a low carbon economy existing
and proposed dam projects are also likely to play a key role in future water and energy management in the region. This conjuncture means a potentially
increasing overlap between PWS Schemes and Dam projects in tropical regions. Improved valuation of any potential watershed service benefit to optimize
dam operations and their benefits to society from the better land management through PWS schemes is crucial to assure both benefits to the performance
of dams and a more sound implementation of the schemes. By developing a geo-referenced Tropical Dams Database (TDD) and combining it with other
recently developed tropical hydro-climatic datasets this research presents a tropics-wide overview of the hydrological value of tropical mountains to dams,
particularly of cloud forest ecosystems, and takes the Andean system of basins as a case study to illustrate how this hydrological value translates to water
productivity, particularly in terms of hydroelectricity. Results highlight the hydrological importance at tropical mountains, especially of cloud forests, to
dams and their relevance for the hydroelectric production in the Andean region. This information is being used currently to indentify PWS Schemes in dam
watersheds in these regions for a more detailed and sophisticated valuation of their potential benefits to society through improving dams performance.
Tropical dam census
Water productivity:
The Andes system of basins
In the case of the highly urbanized Andean region, part of
the runoff collected from just around 10.5% of its
mountainous watersheds (around 389190 km2) is translated
into a significant regional hydroelectric installed capacity, of
at least 20000MW. The system of basins accounts for
around 174 dams with at least 80300Mm3 of water storage
capacity also used for drinking water, irrigation and
industrial purposes.
Therefore, Andean mountains are and will continue to
provide a tangible service supplying large energy demands
in the region. This together with high levels of risk in the
continued provision of such supply due to high urbanization
expansion, deforestation and climate change and still
significant poverty level especially in mountainous areas
means that the Andean region is and will continue to see a
continuous growth in the exploration of PWS Schemes to
The number of dams in the tropics, amounts to around 18770. About 43.3% of
both maintain a satisfactory supply of services and mitigate
these dams are found in Asia (8126), 32.5% in South America (6101), 16.8% in
poverty.
Africa (3149) and 5.5% in Central America and the Caribbean (1033). Only 1.86 of
these dams are found in Australia and less than 0.05 in areas of the Middle East.
This information is useful to help tracking the
implementation of PWS Schemes in dam watersheds in
these regions and to prioritize areas where more detailed
Extent of tropical watersheds contributing to dams and sophisticated valuation studies of their benefits to dams
performance and to society is required.
About 32% of the tropical land masses (around 2.1x107 km2) are found upstream
these dams. These contributing watersheds capture around 24.4% of the tropical
rainfall (about 17260km3) and account for up to 6% of the tropical surface water
balance (about 648km3).
The importance of cloud forests ecosystems to dams
Covering just 4.4% of the upstream area that contributes to tropical dams
(927461km2), the cloud forest sections receive about 15% of the rainfall falling in
these contributing watersheds and account for almost 50% of their surface water
resources. While the average water balance in tropical dam watersheds is of
around 85mm year-1, the average water balance in the cloud forest sections is of
around 157mm year-1. This illustrates the hydrological importance of this particular
tropical forest ecosystem in the context of dam operations.
1. PhD Researcher: luis.saenz_cruz@kcl.ac.uk
2. Reader in Geography: mark.mulligan@kcl.ac.uk