Flood risk reduction and flow buffering as ecosystem services – Part 1: Theory on flow persistence, flashiness and base flow

Abstract

Abstract. Flood damage reflects insufficient adaptation of human presence and activity to location and variability of river flow in a given climate. Flood risk increases when landscapes degrade, counteracted or aggravated by engineering solutions. Efforts to maintain and restore buffering as an ecosystem function may help adaptation to climate change, but this require quantification of effectiveness in their specific social-ecological context. However, the specific role of forests, trees, soil and drainage pathways in flow buffering, given geology, land form and climate, remains controversial. When complementing the scarce heavily instrumented catchments with reliable long-term data, especially in the tropics, there is a need for metrics for data-sparse conditions. We present and discuss a flow persistence metric that relates transmission to river flow of peak rainfall events to the base-flow component of the water balance. The dimensionless flow persistence parameter F p is defined in a recursive flow model and can be estimated from limited time series of observed daily flow, without requiring knowledge of spatially distributed rainfall upstream. The F p metric (or its change over time from what appears to be the local norm) matches local knowledge concepts. Inter-annual variation in the F p metric in sample watersheds correlates with variation in the "flashiness index" used in existing watershed health monitoring programmes, but the relationship between these metrics varies with context. Inter-annual variation in F p also correlates with common base-flow indicators, but again in a way that varies between watersheds. Further exploration of the responsiveness of F p in watersheds with different characteristics to the interaction of land cover and the specific realisation of space-time patterns of rainfall in a limited observation period is needed to evaluate interpretation of F p as an indicator of anthropogenic changes in watershed conditions.

People-Centric Nature-Based Land Restoration through Agroforestry: A Typology

“…As noted Reductions, rather than the expected increases, in streamflow are a common result of tree planting and forest restoration [109] that do not have to come as a surprise. Depending on the environmental conditions an intermediate tree density can be optimal from a groundwater recharge perspective [110], while desirable effects on flood-causing peak flows can be stronger than undesirable reductions in annual water yield [111,112]. Flood control may depend on using trees as part of river restoration [113] rather than blanket reforestation of landscapes.…”

Possible Increases in Flood Frequency Due to the Loss of Eastern Hemlock in the Northeastern United States: Observational Insights and Predicted Impacts

“…Trees exert a fundamental control on the hydrologic cycle through soil shading, canopy interception and storage, root water uptake of soil and groundwater, partitioning of latent heat losses between evaporation and transpiration, and root modification of soil pore size distributions (Brantley et al, ; Knighton et al, ; Sprenger et al, ). Researchers have considered active forest management as a path toward controlling the distribution of catchment water (e.g., Douglass, ; Ford et al, ; Noordwijk et al, ; Schüler et al, ), yet the viability of forest conservation practices as a means of flood management has been questioned (e.g., Soulsby et al, ).…”

Sustainable Agroforestry Landscape Management: Changing the Game

“…The principal concept in all of ecohydrology is that of the water balance, where input (precipitation P or snowmelt in cooler parts of the world) is related to two main pathways out of the system: back to the atmosphere via evapotranspiration (E) and streamflow Q (surface or groundwater flows) and to changes in the 'buffer' of water held inside the system (Figure 7). At timescales of a year or more this buffering can be ignored (except for interannual climate variability), but at the timescale of a rainstorm it is key to reduce downstream flooding risk [41,42]. The principal concept in all of ecohydrology is that of the water balance, where input (precipitation P or snowmelt in cooler parts of the world) is related to two main pathways out of the system: back to the atmosphere via evapotranspiration (E) and streamflow Q (surface or groundwater flows) and to changes in the 'buffer' of water held inside the system (Figure 7).…”

“…Suriname, a country on the Guiana Shield in Latin America, is rich in rainforests and freshwater resources [78,79]. Its average annual rainfall in the area of 2700 mm [80] is an important source of evaporation that precipitates further inland in South America [41]. The Upper Suriname River Basin (USRB) is still mostly covered by primary and secondary forests [81].…”