Landscapes, Ecohydrology & Flood Risk Reduction
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Flood risk in urban centers across the Philippines is increasing due to changes in ecological and hydrological processes. Both global and local drivers are intensifying these changes. Climate change is triggering an increase in hydro-meteorological hazards. Local land cover degradation, urbanization, conversion of floodplains and inappropriate hydro infrastructures have all increased our vulnerability to hydrological hazards. In order to design appropriate responses the role and function of riparian ecosystems in regulation of flood is required to be understood not only in both spatial and temporal contexts, but also in socio cultural and economic contexts. This paper will look at emerging evidence based approaches from landscape ecology and ecohydrology to develop community driven low cost interventions that can better understand and measure land use degradation and direct land use management actions that can aid sustainable flood risk reduction.
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Landscapes, Ecohydrology & Flood Risk Reduction
- 1. Landscapes, Ecohydrology & Floods Understanding of landscape ecology and ecohydrology for reducing flood risk Declan Hearne ENRM 230
- 2. What’s inside Floods and landscapes What evidence based tools can help? How we can employed such tools? What was found out and what are the implications?
- 3. Floods & landscapes Flood risk in urban centers is increasing Drivers of change are both global and local Climate change is triggering an increase in hydro-meteorological hazards. Local land cover degradation, deforestation urbanization and conversion of floodplains have all increased our vulnerability to hydrological hazards.
- 4. Floods & landscapes With a series of devastating flood affecting the Philippines there is a drive to rehabilitate many of the upland degraded landscapes. But to what extent can land use management really play in managing floods? good forest cover reduces flood risk?
- 5. Study objectives To understand how landscape ecology & ecohydrological principles can be applied to reduce flood risk. to employ evidence based approaches that can help quantify understanding about the effect of different land uses in river basins
- 6. theory for guiding change Ecology - living organisms have with respect to each other and their environment. Landscape ecology - relationship between the spatial and temporal arrangement of ecological elements and processes (e.g. the flow of energy, materials & individuals in the environment) Ecohydrology - considers the functional interrelations between hydrology, ecosystem processes and their biota.
- 7. EcohyrdologyZalewski (2010) based on "dual regulation" and harmonization of landscape ecology with human needs, such as flood mitigation, food and energy production, transport and recreation; Dual regulation: regulation of biota by altering hydrology and regulation of hydrology by shaping biota.
- 9. Methods Review of secondary data (maps, bio, physical and social) Conduct of rapid field assessments Conduct of GIS based land assessments Landscape classification Landcover elements (matrix model, based on CPDO indices) Landcover change from 2002 – 2010 Estimation of landscape roughness How we employed the tools?
- 12. Assumptions & limitations Patches of trees can act as filters in the landscape and can have impacts at the river basins scale No ground verification of landscape assessments Low definition used in identification landscape element types (could not differentiate between brush, shrub and open forest - so all are classified as one land cover type Patch density, Edge density, or number of classes are not established The method used for scaling up manning co-efficient to a landscape scale is likely increase the potential for error in final roughness estimations
- 14. Results What was found out
- 17. Defining landscapes Base Map: MGB Geohazards Map 2004
- 18. Defining landscapes Delineation of catchment and high erosion areas
- 19. Defining landscapes Delineation of landscape based on hazards, and field observed socio, production and ecological uses
- 20. Sample Areas Sample Areas of approx 2 km2 was used to measured predominate landscape elements in each landscape Matrix was calculated for each sample area M = SA - (P1+P2+ P3 + P4 … etc) Where M is the matrix landscape element SA is the total area of the sample area P is the total are for individual patch types (e.g. P1 is open forest, P2 is grassland etc)
- 21. SA1: Socio production landscape Introduced Patches (BUA) Remnant Patches (OCF) Disturbance Patches (G)
- 22. SA2: Riparian landscape Open Canopy Grassland Built Up Areas Matrix TP
- 23. Sample Area 3
- 24. Manning Coefficient Manning landscape estimate = n* % area cover Riparian Landscape = 0.011 Socio production L = 0.010 Lower RL = 0.009 The coefficient is mainly a property of the ground surface texture and the changes in water surface elevation.
- 25. Discussion what are the implications?
- 26. Largely fragmented landscapes Matrix landscape is tree plantation/ agriculture (aligned with CLUP) Remnant forest patches ranged between 14 – 20% Social production landscape has lowest observably PD
- 27. Landscape change is subtle, but real Land cover change is not substantial if taken over the total river basin, but 18.4% increase in built area in lowest portions of the riparian landscape (RL) 7% reduction in open forest in the upper sections of the RL Continued degradation was obvious during field assessments The extensive riparian corridor is absent from CLUP Manning coefficient demonstrated the the RL has highest potential to slow water run off from the landscape
- 28. Recommendations Protection of the remaining open forest stands and reforestation efforts to reduced flood risk downstream would be most efficient if they are targeted within the Riparian Landscape. the use of down-slope riparian buffers can attenuate rapid run-off at the local scale to add value to protection and reforestation interventions water water quality and biodiversity objectives should be included Land use management will never stop flooding, the goal must be to able to live with floods and not to eliminate them.
- 29. Gaps…the original paper did not resolve the extent to which floods can be mitigated through land use management (10%, 20%, 30% reduction in flood intensity???) Flood intensity needs to better understood when considering landscapes measures for reducing flood risk (little observed impact in extreme events!) Analysis of soils is critical to improve infiltration or sponge effect (targeted planting should be in sensitive soils.) Species best suited for increasing hydrological roughness needs to be established. methods to ensure sapling can reestablish themselves in eroded and degraded riparian zones.
- 30. Study objectives To understand how landscape ecology & ecohydrological principles can be applied to reduce flood risk. to employ evidence based approaches that can help quantify understanding about the effect of different land uses in river basins
Notas del editor
- sets the scene for what’s coming up in the presentation.
- Jumps us straight into the context for why the subject of flood and landscape was selected. We note that their are both local and global drivers effecting the increase in hydro hazards.
- Notes that the Philippines has been badly effected by recent floods. It also raises 2 critical questions - to what extent can land use management really play in managing floods? and is our assumption that 'good forest cover reduces flood risk' back up by scientific evidence?
- in relation to the context this slide sets the objectives which the study sought to address.
- provides the background theory proven scientific approaches that will be employed to help address or answer the questions raised in our 2 objectives (as set in Slide 5). A key point of this study is its focus on physical process in ecosystem as apposed to the living organisms more traditional address in landscape ecology.Ecohydrology is introduced as a supporting interdisciplinary approach that can complement landscape ecology. a major focus of eco hydrology is of course the movement of water across ecosystems.
- Provides background on the major theory behind ecohydrology. It highlights the importance of dual regulation - how water can alter living communities and vise versa how living organisms can alter the water cycle.
- Highlights the 2 principle under EcoHydrology - noted that there a vast range of areas and elements in a ecosystem that can be managed to improve ecosystem services. In this study we focus on the retention capacity of the landscape ( to retain water movement) and note how in theory this can be enhanced through diversified landscape management.
- Methods adopted in the study. we started with a review of existing data. However since it is poorly studied catchment there was very little characterization data available. CLUP and Geo hazards maps were reviewed. We then had the opportunity to conduct field study with 60 local and International participants. The study tour looked at downstream impacts on urban communities and impacts on the vegetation in the stream channels. After which we visited upstream area to gain perspectives of the state of land cover and to explore possible reasons for the devastating flood last June 28th.
- Location of the Matina River Basin. Noted its in Southern Philippines and within the boundaries of Davao City. It is a very small catchment of approx 81 sq km.
- shows the study tour stops visited in late August 2011.
- highlights the assumptions and limitations of the study. The most critical assumption is that forest patches can play a roles in flood reduction at a landscape scale. The tool used for the landscape assessment was Google Earth. This had limitations in the definition of landscape elements and so to simplify similar element were clustered - i.e. brush and shrub were both considered under open canopy. Because of these limitations I did not attempt to calculate PD, ED or NC. The scaling up on Manning N also may have had errors.
- Refers to an evidence based study which indicates that our first assumption from slide 12 is valid. In basins of less than 100 sq km land use management can have measurable impacts on average flow, peak flows and low flows.
- Results summary. I delineated 3 landscapes based on land cover reviews, hazards maps and socio, production and ecological uses. We then identified 3 sample area for more detailed assessment. Originally the sample no. 3 was targeted to be in the urban landscape but cloud cover in the Google earth image inhibited finding a good sample site. So we shift sample area number 3 back into the lower portion of the riparian landscape.
- In this and the next few slides we look at how I delineated the landscapes. I started with the 2002 city land cover map. This shoed only to landscape types in the matina river basin - urban built up areas and Tree Plantation.
- Delineation of the Matina River Basin
- I overlaid the MGB Geohazard map on google earth and delineated the high and very high area for erosion susceptibility. The assumption being that water as well as soil would be likely to move rapidly in these areas.
- Delineation of landscape based on hazards, and field observation of socio, production and ecological uses.
- Calculating of matrix element and patch elements in the sample areas. The formula for calculating landscape matrix is provided. An assumption is made here that the sample areas are representative of the wider landscapes in which they are situated.
- Detailed look at SA1 in the Socio production landscape. Note in 2010 the introduced patches of built up areas (an increase of 0.42%), other remnant open forest patches and disturbance grassland patch saw little change in area over the 8 years from 2002 - 2010.
- Riparian Landscape. Saw the large loses in open forest cover (-6.6%) and this was supplanted by built up areas. This sample are probably has the greatest Patch density, though this was not measured only observed.
- final sample area reviewed saw large increases in built up areas (+18.4%) . Demonstrating urbanization of agriculture (tree plantation) lands (-17.2%).
- Shows manning coefficient for each of the landscape and how it was scaled up to landscape scale.
- Concludes that the matrix landscape is tree plantation/ agriculture . And that this is in line with the CLUP of 2002. However notes remnant forest patches that ranged from 14- 20% of total landscape area and that this patch are absent from the government land cover maps. This needs to be amended. Also noTed that the socio production landscape is largely man made and has the lowest observes PD.
- Concludes that while the change in landscape are subtle, they are real and might be having real impacts on the movement of energy and material (e.g. the speed and volume of water) across the landscapes. This degradation of landscape was observed during the study tour where vast tracks of open forest had been cleared on very sleep slopes. Chainsaw could be heard during the study tour. The importance of recognizes the riparian landscape in land use map is emphasized. It also noted that manning coefficient demonstrated the importance of forest cover in the landscapes.
- Recommendations - states the need to prioritize protection of remain forests patches and to prioritize reforestation in the Riparian landscapes areas. Highlight the need for man made interventions because of the degraded state of the landscape. But also noted that reforestation and protection should not be considered just for flood control and biodiversity and water quality objectives should also to be consider to insure intervention can be justified from a cost benefit perspective. This point is highlighted as the presenter is aware that severe flood might only happen once every five, 10 0r 25 years. Finally it is highlighted that it would be high risk to expect land management alone to control floods. and states that land management alone will never stop flooding but it can help reduce the risks associated with floods.
- Highlights gaps that if addressed would enhance the existing findings in the paper. Highlighted the need to have realistic expectations of how much land management (back by the science of landscape ecology and ecohydrology) can really mitigate floods. Highlights that land use management has little impact on extreme flood events. Also highlights the importance of soils, trees species and plant management techniques for effective reforestation that lead to reduce risk downstream.
- inclosing we reflect on our two objectives - from slide 5 --- and I believe we can say we have learnt how the theory of landscape ecology and ecohydrology can be applied to improve land manage for reducing flood risk at a landscape scale.