water, forests and footprints – finding the right scale for sustainability by kevin bishop
DESCRIPTION
In his presentation Kevin Bishop tried to unfold how forests impact water partitioning at different scales. At a local catchment scale, a removal of forests usually increases the total flow, always increases the peak flows, and can increase as well as decrease the base flow. Although there exists some ambiguity regarding the role of forests, all scientific studies confirm that forests have larger evapotranspiration (ET) than most other land uses. (Evapotranspiration is the sum of evaporation and plant transpiration from the Earth's land surface to atmosphere) However, there are studies that consider impacts of forests on water availability for annual mass balances at the local watershed level misleading. More at www.siani.seTRANSCRIPT
Water, forests and footprints – finding the right scale for sustainabilityProf. Kevin BishopUppsala University& Swedish Univ.of Agricultural Sci.
Less than 4% forest in Blue NileDeforestation widely blamed for water problemsWill more trees help? Or will they “steal” water?
65 %
35 %M.Falkenmark March 09
Green-Blue Water sees forests as consumers of water
Plynlimon – Hydrologist HeavenDocumented how forests took water – at the the 2 km2 catchment scale
My own background Digging in small catchments –
Miss a bigger picture?
©Bill Waterson
Hydrology and Forests in the Blue Nile:
What can be learned from half a century of observations and community perception for water management?
Solomon Gebreyohannis
Addis Ababa UniversityandSwedish University of Agricultural Sciences
Popular Perception vs Science
Popular hopes for reforestation:– Increase dry-season flow– Decrease erosion
But science suggests…
While Peak flows and erosion will decreaseTotal flow will probably decreaseDry season flows will probably decrease, (but site-specific information needed)
Interdisciplinary PhD Thesis: Half a century of quantitative and qualitative observations
• A dozen catchments have over 40 years of daily flow data.
• Remote imagery exists for land use/land cover change analysis
• Community perception will be used help in the analysis.
*= Flow gauge
Some large declines in forest area
1957 Landcover16% Forest = Green
2000 2% Forest
Statistical and Modeling Analyses:No obvious deforestation impact
y = 0.0008x + 0.3844
y = 0.0321x - 17.170
20
40
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1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Pea
kflo
w (m
3 /s)
00.511.522.533.544.5
Bas
eflo
w (m
3 /yea
r)
Peakflow (m 3̂/sec) Baseflow (m 3̂/yr)
Community Perception: A complex understanding of the forest-water relationship
Deforestation influence on streamflow:Revisting what has science “proven”
Deforestation
Baseflow sometimes increases sometimes decreases
Region-specific data needed to know response
Total flow usually increases
Peakflow always increases
04/10/2023 13
Watershed Mass Balance
Precipitation (P)
Evaporation+
Transpiration (ET)
Runoff (Q)
Are Forests Good for Water Resources?
The Hydrologic Cycle: Trees remove water at one point, return it to the region
The Forest-Water Debate: Supply vs. Demand-Side
Demand-side:Increasing forest cover reduces runoffEcosystems subtract from the water budgetStrong observational basis (<2 km2)
Supply-side:Increasing forest cover positively impacts precipitation
and runoffSometimes labeled the “romantic” or even
mythological viewLimited empirical evidence Regional Modeling is the best evidence
Source data generously provided by Michael Bosilovich, NASA
Balatic Recycled ET Ocean
Annual 40% 60%
Summer 60% 40%
DJF MAM JJA SONBaltics
0
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160
Water Recycling Modelled at Regional Scales
Source data generously provided by Michael
Bosilovich, NASA. Highlighting indicates Terr_shr
> Oc_shr.
Note: local share included in terrestrial share.
DJF MAM JJA SONMississippi
020406080
100120140160
DJF MAM JJA SONMacKenzie
0
20
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60
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120
DJF MAM JJA SONSiberian
020406080
100120140160180
DJF MAM JJA SONBaltics
020406080
100120140160
DJF MAM JJA SONHUB
0
50
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DJF MAM JJA SONTibet
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DJF MAM JJA SONGTR
050
100150200250300350400450
DJF MAM JJA SONCAT
020406080
100120140160180
DJF MAM JJA SONAmazon
050
100150200250300350400
Average Estimated Precipitation in Major River Basins by Source (1948-1997)
Should Egypt be more concerned about deforestation of the Congo that dams on thd Blue Nile?
Much Precipitation is Recycled Evaporation:East African over 50% of rain from trees
The Forest Water Yield Debate:A Question of Scale
• All Agree: Trees Increase Evapotranspiration– Demand-side View: Reduces runoff – Supply-side View: Recycles Water, Increases Rain
• View point depends on Scale– Demand at Small Scale– Supply at Large Scale
What is Forest ET’s impact on precipitation??
Forest and wetland cover are the two most efficient methods for promoting evapotranspiration (ET)
Only oceans can evaporative as effectively- 90% of ocean evaporation falls back on the ocean
Cropland exhibits comparatively low evaporative efficiency
Land conversions to agriculture will reduce precipitation
Between 2000-2005, global forest cover has decline by 3% (Hansen et al 2010)
Suggests a 4.7-5.3% decline in global precipitation
Conclusions • Forest cover important role for the global hydrologic cycle.
• Increasing forest cover increases regional precipitation and runoff .
• Global impact of forest cover does not rule out local demand.
• Trans-boundary impacts of local decision-making about forests.
• Forest provide ecosystem services beyond biomass
M.Falkenmark March 09
Remember Recycling!
Are forests good for water and food security in Ethiopia?
Swedish Ministry of Foreign Affairs as Project on global food security
Two MSc Students to the Koga Irrigation Dam
Two PhD Students fromCentre for Natural Disaster Science
New Interdisciplinary research initiativeby the Swedish Government
Climate Adaptation = Disaster Mitigation