Flood peak data for focus catchments in Costa Rica, Ecuador, Chile and Argentina are analyzed to test the hypothesis that, as the size of the hydrological event increases, the effect of forest cover on the peak discharge becomes less important. Previous research suggests that this hypothesis may hold for small catchments (less than 1 km 2) but the pattern is less clear for large catchments. The principal study results are for small paired catchments (0.6-10 km 2) with different forest covers (forest/pasture) in highland Ecuador and a small (0.35 km 2) plantation catchment in southern Chile subjected to logging. The former were analyzed by comparing the corresponding peak discharges for given rainfall events, the latter by comparing the relationships between peak discharge and rainfall event size for the pre-and post-logging periods. In all cases there is relative or absolute convergence of the responses as discharge increases, with convergence likely for flood return periods of around 10 years. More limited data for larger catchments which have undergone either deforestation or afforestation (131 km 2 in Costa Rica and 94-1545 km 2 in Chile) suggest that the percentage change in forest cover must exceed 20-30% to provoke a measurable response in peak discharge; convergence of peak discharge response at high flows (return periods of around 5 years) for the different forest covers may then be observed. For a 12.9-km 2 snowmelt-affected catchment in Tierra del Fuego, Argentina, extreme floods require rain-on-snow events but the data are not sufficient to quantify the complex relationship between forest cover, event return period and peak discharge. In general, forest cover is unlikely to reduce, significantly, peak discharges generated by extreme rainfall but may still offer substantial mitigation benefits for moderate (i.e. more frequent) rainfall events.

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The EPIC FORCE project aimed to develop science-based policy recommendations for integrated forest and water resources management, relevant to extreme events for Costa Rica, Ecuador, Chile and Argentina. Data analysis and model application support the hypothesis that, as the size of the flood peak increases, the effect of forest cover becomes less important. Guidelines for integrated water and forest resources management are developed which recognize this effect but emphasize the role that forests play in reducing the flood levels of more moderate events. The research findings are transferred to policy-making for the four focus countries via a set of policy briefs, taking into account the institutional frameworks, achievable policy objectives and key stakeholders.

La conjunción de humedales costeros y continentales en zonas semiáridas y en adyacencias urbanas, representa un valioso patrimonio socio-ambiental, sujeto a las tensiones que la expansión urbana genera, especialmente si se manifiesta con altas tasas de crecimiento. El presente artículo aborda el problema de los cambios físicos sobre humedales provocados por la expansión urbana acelerada en el contexto mencionado, identificando factores agravantes. Se estudió el caso de Río Grande, ciudad costera de la estepa de Tierra del Fuego, Argentina, cuyo crecimiento fue impulsado desde 1972 por políticas de promoción industrial. Los humedales fueron identificados, clasificados y cartografiados mediante análisis multiespectral de imágenes de satélite. La expansión urbana se delimitó según tres períodos vinculados a variantes en las políticas de promoción. El análisis espacio-temporal evidencia correspondencia entre pulsos de fluctuación de las políticas, con la dinámica de la expansión urbana y ocupación de áreas naturales. Un tercio de la expansión urbana fue a expensas de la desaparición de humedales, con saldo adicional de unidades fragmentadas. Se analizan externalidades, no siempre evidentes, resultantes de la urbanización de estos ecosistemas y se concluye en la significación de los asentamientos informales, así como la falta de planificación como factores que incrementan la pérdida de humedales.