Paper discussion of Wohl et al. 2012 by Chris Nytch, CIAM 6117, UPR Rio Piedras

2. srh.noaa.gov

3. The Hydrology
of the Humid Tropics
Wohl, E., Barros, A., Brunsell,
N., Chappell, N. A., Coe, M.,
Giambelluca, T., ... & Ogden, F.
(2012). The hydrology of the
humid tropics. Nature Climate
Change 2(9): 655-662.
Outcome of workshop held in
Hilo, Hawaii in 2011
warnercnr.colostate.edu

4. Review Article
Various perspectives from the international
scientific community
Examines the role hydrology plays in the
functioning of the humid tropics in the
anthropocene
State of knowledge
Critical research needs to aid in understanding tropical
hydrology in context of rapid environmental change

5. Tropical Hydrology – summed up
“All aspects of tropical hydrology — from fluxes of energy
and water within the atmosphere, to those within
vegetation, land surface and subsurface systems, to stream
outputs of water, sediment and solutes — are distinguished
from other regions of the globe by substantially greater
spatial and temporal variability, higher magnitudes,
pronounced spatial gradients, and consequently the
potential for rapid and significant change in response to
anthropogenic alterations and associated water fluxes.”
(Wohl et al. 2012, p. 657)

6. 1. Overview of the Humid Tropics
Between ~ 25° Latitude North and South
1/5 of global land surface
Precip>evap for >270 days/yr
Tropical storms due to wind and moisture patterns
Greatest amount of runoff
High intensity of land-cover disturbance through forest
cutting
Hydrological cycle with processes spanning wide range
of spatial and temporal scales
en.wikipedia.org

7. Atmospheric components
Image sources: serc.carleton.edu;
science.nasa.gov;
iac.ethz.ch
GLOBAL
LOCAL
MICRO

8. Land Components
stri.si.edu
• Hydrologic forcing
• Intense convection above
rainforests
• Atmospheric latent heating
along mountain ranges
• Mountains modulate and
harvest atmospheric moisture
• Supplies water via rivers to
human pops
(e.g., 1.4 billion in southeast
Asia)
news.nationalgeographic.com

9. Moisture Cycling (compared to mid-
latitudes
Warmer and uniform
temps
Large inter-annual and
sub-seasonal variability
More intense
precipitation and spatial
gradients of precipitation Photo credit: Jorge Ortiz
Photo credit: Jorge Ortiz
srh.noaa.gov

10. Río Mameyes at Puente Roto, El Yunque
Image source: Jorge Ortiz
Image source: Jorge Ortiz
• Spatial and Temporal Gradients
(cont.)
Moisture Cycling (cont.)

11. Moisture Cycling (cont.)
Greater water and
terrestrial material
fluxes
rapid weathering
greater river flows
and sediment
loads and nutrient
transport
Wohl et al. 2012

12. Moisture Cycling (cont.)

13. Water and Land Cover
Water flow and energy/carbon exchange is tied to
vegetation type, amount, age, density
wikipedia.org

14. (Tropical) land cover
is highly dynamic
due to rapid shifts in
patterns of land use
at multiple scales
Global
Water and Land Cover (cont.)
Foley et al. 2005

15. Water and Land Cover
Local scales
Grau et al. 2003
www.prgap.org

16. Water and Land Cover (cont.)
Important feedbacks from land cover to climate and water
fluxes (and vice versa) at local and global scales
empowermagazine.com

17. Fluxes of energy,
water, and carbon and
the dynamical
processes that alter
these fluxes
Increases in CO2
changes in climate
patterns
tropical vegetation
responses
hydrologic fluxes
Water and Land Cover (cont.)
Bonan 2008

18. 2. Anthropogenic Modifications
earnthis.net

19. Anthropogenic Modifications (cont.)
Population increase/pressure
homosapienssaveyourearth.blogspot.com
globalchange.umich.edu

20. Anthropogenic Modifications (cont.)
Fragmentation and effects on hydrological fluxes
Alterations of mass and energy cycling, more intense
at local level and point source emissions

21. Anthropogenic Modifications (cont.)
Land use/cover changes
Small-scale shifting cultivation
• Large-scale industrial
agriculture
en.wikipedia.org
• Selective felling

22. Anthropogenic Modifications (cont.)
Significant impacts on local and regional hydrology,
stream form and function
Brazil: Reduced evapotranspiration, shifts in rainfall
phenology, dry season extended, increased discharge
Increased sediment yield with commercial forestry, road
construction and mining.
Wohl et al. 2012, Figure 3: Example of how
evapotranspiration rates in disturbed rainforests
in the dry season are related to land-use history.
Wohl et al. 2012, Figure 4: Schematic of local and regional
hydrological response to deforestation.

23. Anthropogenic Modifications: Climate Change
Direct alteration of tropical precipitation regime and other
aspects of the hydrological cycle
www.ucar.edu

24. Climate Change (cont.)
Global hydrological processes are expected to
accelerate as temps rise and air moisture increases
Variable regional/local responses of precipitation
patterns to climate change across tropics
Diverse implications for geomorphic and hydrologic patterns
and the associated human activities (e.g., agriculture)
IPCC 2007

25. Anthropogenic Modifications (cont.)
Future drivers of alterations to
tropical hydrosphere
Freshwater supply
Food production
Energy development
Modifications of local land surface
will propagate from deep
groundwater to troposphere
Impacts are variable across regions in
time and space
Dynamics best explained in the
context of coupled human-natural
systems.
social and economic motivations
governing land-use change
environment.nationalgeographic.com
wiki.resalliance.org

26. 3. Research Vision
Urgent need to characterize the ‘accelerated’ nature of the
tropical water cycle.
Image source: Alonso Ramirez
Holistic framework for
observing and
monitoring moisture
cycling
Emphasis on
subsurface to
troposphere
interactions across
strong physiographic
and ecological
gradients

27. Three Main Research Areas
Moisture cycling
Catchment processes
Long-term data acquisition and organization

28. Moisture Cycling
More vigorous hydrologic cycle due to precipitation
variability
Accelerated geomorphic and ecologic responses
Difficult to project nonlinear feedbacks between
atmospheric humidity and associated water fluxes
Models that
include
groundwater
dynamics
Role of land-
cover patterns
on water fluxes
and predicting
influences of
future change
In context of
warming climate
Cross-scale
assessment
of spatial
and
temporal
variability
Emphasis on
integrated
measuring,
modeling and
quantification of
water fluxes
across the land-
atmosphere
continuum and
between moisture
reservoirs

29. Tropical Hydrological Cycle
Wohl et al. 2012

30. Empirical/field based studies on input to humid tropical
streams, stream form and function across diverse sites
Environmental effect on spatial distribution of precipitation
(and consequently runoff and sediment transport)
How human landscape alterations affect evapotranspiration
and runoff ratio in different environments
Catchment Processes
Bisley Watershed 1
Research tracts in the Luquillo Experimental Forest (Scatena 1989)

31. Catchment Processes (cont.)
Biogeochemical cycling in tropical streams
Magnitudes and rates of different flow pathways, transport and
cycling of carbon and other nutrients
Microbial processing rates and food web responses
Chemical inputs from precipitation, at variable time scales
Role of dust inputs
Anthropogenic alterations
Integrated study of chemical,
physical, and biological
processes that shape earth’s
surface
Role of floods and sediment
loads during cyclonic events

32. Long-term Data Acquisition & Organization
Lack of high-quality hydrological data
from tropics
Need integrated data collection from
deep subsurface through troposphere
Need long-term monitoring to catch low-
frequency dynamics
Need network of coordinated, concurrent
experiments, open-platform databases
Need more micro-meterological tower sites
across all regions, coupled with remote sensing
Satellite-based monitoring and radar imagery
Synthesis of technologies in hydrological
models of atmospheric/ecosystem interactions

33. Positive attributes of the article
Well-written & easy to read
Extensively researched
Multi-faceted and multiple scales
Good examples and supporting figures
Focus on detailed research themes/questions
Emphasis on cross-site coordination and infrastructure
needs

34. Critiques
There’s so much, --
where to begin?
Where’s Luquillo?
What about urban
hydrology?
Link with coastal
processes?

35. Questions/
Comments?
Aliraqi.org

36. Literature cited
Bonan, G.B. 2008. Forests and climate change: forcings, feedbacks, and the climate benefits of
forests. Science 320(5882):1444-1449.
Foley, J.A., R. DeFries, G.P. Asner, C. Barford, G. Bonan, S.R. Carpenter, F.S. Chapin, M.T. Coe, G.C. Daily, H.K. Gibbs,
J.H. Helkowski, T. Holloway, E.A. Howard, C.J. Kucharik, C. Monfreda, J.A. Patz, I.C. Prentice, N. Ramankutty, and P.K.
Snyder. 2005. Global Consequences of Land Use. Science 309:570 - 574.
Grau, H. R., T. M. Aide, J. K. Zimmerman, J. R. Thomlinson, E. Helmer, and X. Zou. 2003. The ecological consequences
of socioeconomic and land-use changes in postagricultural Puerto Rico. Bioscience 53:1159–1168.
IPCC, 2007: Summary for Policymakers. In: Climate Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S.,
D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press,
Cambridge, United Kingdom and New York, NY, USA.
Milliman, J. D., & Meade, R. H. 1983. World-wide delivery of river sediment to the oceans. The Journal of Geology: 1-21.
Scatena, F. N. 1989. An introduction to the physiography and history of the Bisley Experiment Watersheds in the
Luquillo Mountains of Puerto Rico. General Technical Report SO-72:1–22. U.S. Department of Agriculture, Southern
Forest Experiment Station, New Orleans.
Wohl, E.; Barros, A.; Brunsell, N.; Chappell, N.A.; Coe, M.; Giambelluca, T.; Goldsmith, S.; Harmon, R.; Hendrickx, J.;
Juvik, J.; McDonnell, J. J.; Ogden, F.. (2012). The hydrology of the humid tropics. Nature Climate Change 2(9): 655-662.