Flood risk reduction and flow buffering as ecosystem services

Flood damage reflects insufficientadaptation of human presence and activity to location and variability of riverflow in a given climate. Flood risk increases when landscapes degrade,counteracted or aggravated by engineering solutions. Efforts to maintain andrestore buffering as an ecosystem function may help adaptation to climatechange, but this require quantification of effectiveness in their specificsocial-ecological context. However, the specific role of forests, trees, soiland drainage pathways in flow buffering, given geology, land form and climate,remains controversial. When complementing the scarce heavily instrumented catchmentswith reliable long-term data, especially in the tropics, there is a need formetrics for data-sparse conditions. We present and discuss a flow persistencemetric that relates transmission to river flow of peak rainfall events to the base-flowcomponent of the water balance. The dimension-less flow persistence parameter Fp is defined in a recursive flow model and can be estimatedfrom limited time series of observed daily flow, without requiring knowledge ofspatially distributed rainfall upstream. The

Fp metric(or its change over time from what appears to be the local norm) matches localknowledge concepts. Inter-annual variation in the Fp metric in sample watersheds correlates withvariation in the “flashiness index” used in existing watershed health monitoringprogrammes, but the relationship between these metrics varies with context.Inter-annual variation in Fp alsocorrelates with common base-flow indicators, but again in a way that variesbetween watersheds. Further exploration of the responsiveness of Fp in watersheds with different characteristics tothe interaction of land cover and the specific realisation of space–timepatterns of rainfall in a limited observation period is needed to evaluateinterpretation of Fp asan indicator of anthropogenic changes in watershed conditions.