AGU Hydrology Section Newsletter!

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Referencesmaximum carbon gain under dynamic soil moisture, Adv.
Water Resour., 62, 90−105.
Manzoni, S., G. Katul, and A. Porporato (2014a), A
dynamical system perspective on plant hydraulic failure,
Water Resour. Res., 50(6), 5170−5183.
Manzoni, S., S. M. Schaeffer, G. Katul, A. Porporato, and J.
P. Schimel (2014b), A theoretical analysis of microbial
eco-physiological and diffusion limitations to carbon
cycling in drying soils, Soil Biol. Biochem., 73, 69–83.
Manzoni, S., G. Vico, G. Katul, S. Palmroth, and A.
Porporato (2014c), Optimal plant water-use strategies
under stochastic rainfall, Water Resour. Res., 50(7),5379−5394.
Roberts, J. (1983), Forest transpiration - A conservativehydrological process, J. Hydrol., 66, 133−141.
Schimel, J. P., T. C. Balser, and M. Wallenstein (2007),
Microbial stress-response physiology and its implications
for ecosystem function, Ecology, 88, 1386−1394.
Todd-Brown, K. E. O., F. M. Hopkins, S. N. Kivlin, J. M.
Talbot, and S. D. Allison (2012), A framework forrepresenting microbial decomposition in coupled climate
models, Biogeochemistry, 109, 19−33.

Cowan, I. (1986), Economics of carbon fixation in higherplants, in On the Economy of Plant Form and Function,edited by T. J. Givnish, Cambridge Univ. Press,Cambridge, U.K., pp. 133−170.
Evans, S. E., and M. D. Wallenstein (2013), Climate change
alters ecological strategies of soil bacteria, Ecol. Lett., 17,
155–164.
Hunt, A. G., and R. P. Ewing (2003), On the vanishing ofsolute diffusion in porous media at a threshold moisture
content, Soil Sci. Soc. Am. J., 67, 1701−1702.
Jarvis, P. G., and K. G. McNaughton (1986), Stomatal controlof transpiration - Scaling up from leaf to region, Adv.
Ecol. Res., 15, 1−49.
Lennon, J. T., Z. T. Aanderud, B. K. Lehmkuhl, and D. R.
Schoolmaster (2012), Mapping the niche space of soil
microorganisms using taxonomy and traits, Ecology, 93,1867−1879.
Manzoni, S., and G. Katul (2014), Invariant soil water
potential at zero microbial respiration explained byhydrological discontinuity in dry soils, Geophys. Res.
Lett., 41(20), 7151−7158.
Manzoni, S., G. Vico, S. Palmroth, A. Porporato, and G.
Katul (2013), Optimization of stomatal conductance for!

A!Fellow!Speaks:!Opportunities!and!Fortunes!in!Global!Hydrology!
Taikan Oki
The University of Tokyo
Even though I have been a member of AGU for morethan two decades, I paid no attention to the honor ofbecoming an AGU Fellow because I thought it wasnone of my business. After I
was notified that I waselected a Fellow, I was bothhumbled and honored torealize the prestige thisrecognition carries and toknow that I am the firstJapanese AGU Fellow in
the Hydrology Section. I
would like to extend my sincere gratitude to thecolleagues who spent special efforts to nominate me.

Earth sciences, such as meteorology, oceanography,and geology. As Bras et al. [1987] pointed out, there
was an impending need to build a more coherent
understanding of the global water cycle in its fullcomplexity.
As a master’s student, I chose to work on research
related to orographic rainfall, because I thought rainfall
is the major driver of floods and droughts andfundamental to the advancement of hydrology. I tried
to develop a simple atmospheric model, which could
relate upwind areas with orographic rainfall
distribution estimated from rain gauge network data. Iwas very lucky that I had the opportunity to present theresults of my master’s thesis in the Pacific International
Seminar on Water Resources Systems in Tomamu,
Hokkaido, Japan, in summer in 1989. Prof. Soroosh
Sorooshian coorganized the meeting, and strongly
encouraged me to submit the results I presented toWRR, of which he was the editor at that time. I knew
nothing about submitting a journal paper, but Sorooshhelped me a lot, and finally I could publish my result as
an article in WRR [Oki et al., 1991].

In 1987, when I entered the Graduate School at The
University of Tokyo, I came across the article of Braset al. [1987], which termed Hydrology in the late 20thcentury as “The forgotten Earth science.” At that time,hydrological sciences supported human well-being by
reducing risks associated with extremes (scarcities andexcess of water) through management. However, thework was largely isolated from other tightly coupled

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potential capability of 4DDA data to estimate terrestrial
water balances through the combined use of global
precipitation observations and large basin riverdischarge based on the atmospheric water balance(AWB) method. Oki et al. [1995] opened the door to
global water balance studies by AWB in the modernera. Our approach, using 4DDA data, is now
commonly applied to estimate global water balances,even though reanalysis data, the postprocessed version
of 4DDA data, is more popular than operational
analysis data.
Afterward, I had an opportunity to spend 2 years atNASA/GSFC as a visiting scientist, and had some freetime to work on time-consuming research such as
manual correction of a global river channel network,
named “TRIP” [Oki and Sud, 1998]. I was also
fortunate to have an opportunity to participate to the 2ndphase of the global soil wetness project (GSWP2), andvalidated the accuracy of the global water balance
estimated by 11 land surface models (LSMs), that are apart of GCMs and provide lower boundary conditions
to the atmosphere, with a simple river routing scheme[Oki et al., 1999]. TRIP and the river routing scheme
were widely adopted by several GCMs in the world, forexample, six out of 23 future projections employed in
the 4th Assessment Report of the Intergovernmental
Panel on Climate Change (IPCC) utilized TRIP. Even
now, TRIP is coupled within a latest Earth System
Model and a GCM. In summary, Oki and Sud [1998]
filled a missing link in the water cycle of GCMs andexpanded their utility into river flood events.

Figure 1. Vertically integrated annual water vapor
convergence (mm year-1) mean from 1989 to 1992,
updated from Oki et al. [1995]. Positive value
corresponds to annual excess of precipitation overevapotranspiration. Slight negative values over land aremostly due to the limitation of the accuracy of themethodology and data, but partially regarded as theimpacts of irrigation, with which evapotranspiration fromcropland can be larger than local precipitation.

Being a member of the research group of Prof. Katumi
Musiake at IIS/UT, whose research was dedicated tourban hydrology, I felt at that time isolated in pursuing
my interests in atmospheric modeling. However, I had
an opportunity to study physical climatology from Dr.
Kooiti Mauda using a text by Prof. Oort (publishedlater as a book [Peixöto and Oort, 1992]). I wasextremely fascinated with the concept of atmosphericwater balance [e.g., Peixöto, 1970; Peixöto and Oort,1983] and eager to update the estimates.

I’m quite happy to see that Oki et al. [1999] establisheda framework for evaluating global water cycles via offline (uncoupled with atmosphere) simulation of LSMs
combined with river routing schemes. At present, theframework is commonly used to assess LSM accuracy
and improve them by thorough validation, andcalibration to observed river discharge. The frameworkis also useful for translating climate change–drivenchanges to hydrological cycles (projected by GCMs)
into socially relevant information, such as changes in
the frequency of floods and droughts [e.g., Nohara etal., 2006; Hirabayashi et al., 2008]. The 2nd phase of
the Global Soil Wetness Project (GSWP2) also utilized
this framework [Dirmeyer et al., 2006], and acomprehensive review of the global hydrologic cycle
and world water resources based on the estimates fromGSWP2 were published in Science [Oki and Kanae,2006]. Establishing a scientific illustration of the globalhydrological cycle (Figure 2) has been one of my

Fortunately, the 1980s were the dawn of fourdimensional data assimilation (4DDA) of global
atmosphere. I was really excited to calculate thevertically integrated water vapor convergence (Figure1) utilizing operational analyses by ECMWF and JMA,
even though I had to handle several dozen magnetic
tapes at the computer center. Another fortune was thatProf. Murugesu Sivapalan participated in IAHS inYokohama, Japan, in 1993; he also gave a seminar atIIS/UT, and he found my research on atmosphericwater balance interesting. He invited me to a workshop
in Robertson in 1994, and I could publish the results[Oki et al., 1995] in the special issue of Hydrological
Processes, for which Siva was the guest editor. I’ll
never forget how enthusiastically Siva helped merevise and improve the paper. I believe Oki et al.
[1995] was one of the first papers to demonstrate the15!

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Figure 2. Global hydrological fluxes (1000 km3 yr-1) and storages (1000 km3) with natural and anthropogenic cycles aresynthesized from various sources. Big vertical arrows show total annual precipitation and evapotranspiration over land andocean (1000 km3 yr-1), which include annual precipitation and evapotranspiration in major landscapes (1000 km3 yr-1)
presented by small vertical arrows; parentheses indicate area (million km2). The direct groundwater discharge, which isestimated to be about 10% of the total river discharge globally, is included in river discharge. The values of area sizes forcropland and others are corrected from original ones. From Oki and Kanae [2006].

dreams and goals, and I felt really accomplished withthe publication.

Current hydrology has a capability to monitor,
understand, and predict global hydrological cycles ofsocial-ecological systems, combining both human andnatural systems. I am gratified to see that globalhydrology has a prominent place among other Earthsciences now. I cannot list the names of all mycolleagues who contributed to the development of thefield, either as a student, as a postdoctoral fellow, or asa collaborator, but I appreciate very much their untiring
dedication and significant contributions. I feel I havebeen just lucky in my research life, but I’m very proud
to have witnessed the evolution of global hydrology as
one of Earth system sciences.

However, real hydrological cycles are often influenced
by anthropogenic activities, such as reservoir
operations and water withdrawals for human needs, anddiffer substantially from natural hydrological cycles.
Even though human withdrawals are indicated, Figure
2 critically lacks the artificial reservoirs. The first
integrated water balance and water resources model
considering major human interventions on a global
scale was developed by Hanasaki et al. [2008], named
as H08. H08 is coupled with submodels of reservoir
operation, human water withdrawal, environmental
flow, and crop growth, in addition to a natural waterbalance sub-model. Recently, the human intervention
components were transplanted into an LSM, which wasthen applied to assess the impacts of changes in theterrestrial water storage on trends in the global meansea level [Pokhrel et al., 2012].

References
Bras, R., P. S. Eagleson, E. K. Turner, and R. M. Parsons(1987), Hydrology, the forgotten Earth science, Eos
Trans. AGU, 68, 227.
Dirmeyer, P. A., X. Gao, M. Zhao, Z. Guo, T. Oki, and N.
Hanasaki (2006), GSWP-2 - Multimodel analysis andimplications for our perception of the land surface,
Bull. Am. Meteorol. Soc., 87, 1381−1397.
Hanasaki, N., S. Kanae, T. Oki, K. Masuda, K. Motoya, N.
Shirakawa, Y. Shen, and K. Tanaka (2008), AnThe field of global hydrology today has certainly
evolved and established itself nearly 3 decades afterBras et al. [1987] led the call for greater prominence.

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integrated model for the assessment of global water
resources - Part 1: Model description and input
meteorological forcing, Hydrol. Earth Syst. Sci., 12,
1007−1025.
Hirabayashi, Y., S. Kanae, S. Emori, T. Oki, and M. Kimoto(2008), Global projections of changing risks of floods
and droughts in a changing climate, Hydrol. Sci. J.,
53(4), 754−772.
Nohara, D., A. Kitoh, M. Hosaka, and T. Oki (2006), Impactof climate change on river discharge projected bymultimodel ensemble, J. Hydrometeorol., 7(5),1076−1089.
Oki, T., and S. Kanae (2006), Global hydrological cycles andworld water resources, Science, 313(5790), 1068−1072.
Oki, T., K. Musiake, and T. Koike (1991), Spatial rainfall
distribution at a storm event in mountainous regions
estimated by orography and wind direction, Water
Resour. Res., 27, 359−369.
Oki, T., K. Musiake, H. Matsuyama, and K. Masuda (1995),
Global atmospheric water balance and runoff from large
river basins, Hydrol. Proc., 9, 655−678.

Oki, T., T. Nishimura, and P. Dirmeyer (1999), Assessmentof annual runoff from land surface models using Total
Runoff Integrating Pathways (TRIP), J. Meteorol. Soc.
Jpn., 77, 235−255.
Oki, T., and Y. C. Sud (1998), Design of Total Runoff
Integrating Pathways (TRIP) − A Global River Channel
Network. Earth Interact., 2, 1–37.
Peixöto, J. P. (1970), Pole to pole divergence of water vapor,Tellus. 22, 17–25.
Peixöto, J. P., and A. H. Oort (1983), The atmosphericbranch of the hydrological cycle and climate, inVariations in the Global Water Budget, D. Reidel,Dordrecht, Netherlands, pp. 5–55.
Peixöto, P., and A. H. Oort (1992), Physics of Climate, Am.
Inst. of Phys., Washington, D. C., 520 pp.
Pokhrel, Y. N., N. Hanasaki, P. J.-F. Yeh, T. J. Yamada, S.
Kanae, and T. Oki (2012), Model estimates of sea-levelchange due to anthropogenic impacts on terrestrial
water storage, Nat. Geosci., 5, 389−392.

A!Fellow!Speaks:!A!“TOGA!COARE”!Program!for!Continental!Hydrology!and!
Hydrometeorology!
Ana P. BarrosDuke University
It’s been roughly 25 years of unexpected privilege
since my early days as a graduate student at theUniversity of Washington, forwhich I am deeply grateful.
Born in Angola in theheadwaters of the Congo River
Basin, one of my earliest
memories is that of watching
Neil Armstrong step on themoon in 1969, a grainy movie
on an odd screen, a momentous
event played again and again on
an improbable shop window in downtown Luanda on
the day of my birthday. Twenty-something years later,NASA’s EOS (Earth Observing System) program wasin many ways the “stepping on the moon” for EarthSciences. For us in Hydrology and Hydrometeorology,
it was a “watershed” moment, with the global planet as
study domain and unprecedented observations
available over unprecedented ranges of spatial andtemporal scales.

of interdisciplinary “many – a – hyphen” science(hydro-eco-geo-met-…..) and scientists. Global
observations highlighted the importance of climate andorography in the organization of the Earth’s watertransfers and moisture transport from remote to local
scales. New satellite observations brought the Water
Cycle to the forefront of Earth Sciences.
From seasonal albedo changes of 30% at spatial scalesof 10s to 100s of km2, to the diurnal cycle of subdaily
precipitation variability and soil water storage, waterand energy budget closures are within reach atmesoscales. We find that, in the context of the coupled
land-atmosphere system, it is the spatial range of water
cycle teleconnections that determines the effective
boundaries of the River Basin including an airshed thatspans the regional moisture source regions, and alandshedthatpartitions
rainfall,distributes
groundwater between basins below mountain ranges,
and delivers runoff to the canonical terrestrial outlet.
Upstream and downstream are space-time varying
concepts: earlier studies showed that cutting trees in theAmazon changed rainfall there and downwind in theAndes; recent studies show that cutting trees in theAndes changes the rainfall there and over the Amazon
Basin. “Everybody lives downstream” as the world

EOS observations of the Dynamic Earth and theincreasing data analysis, synthesis, and modelingcapacity afforded by High-Performance Computing
prompted new research directions and the development

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