Preliminary Concepts for a Surface Water ESSP Satellite Mission

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Preliminary Concepts for a Surface Water ESSP
Satellite Mission
P. Houser, D. Lettenmaier, D. Alsdorf
ESSP Presentation at GSFC October 8, 2003 Funded
by NASA Terrestrial Hydrology Program
www.swa.com/hydrawg/
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Outline
Amazon Floodplain (L. Hess photo)

• The Lack of Global Discharge and Water Storage
  Change Measurements
• Resulting Science Questions
• Why Satellite Based Observations Are Required to
  Answer These Questions
• Potential ESSP Solutions

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Compelling Science
This presentation is published in these two
articles, which are derived from discussions
amongst members of the NASA Surface Water Working
Group.
D. Alsdorf and D. Lettenmaier, Tracking fresh
water from space, Science, vol. 301, pp.
1491-1494, September 12, 2003. D. Alsdorf, D.
Lettenmaier, C. Vorosmarty, and the NASA Surface
Water Working Group, The need for global,
satellite-based observations of terrestrial
surface waters, EOS, vol 84, pp. 269-276, 2003.
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Lack of Global Discharge
Singular gauges are incapable of measuring the
flow conditions and related storage changes in
these photos of the Amazon floodplain whereas
complete gauge networks are cost prohibitive.
The ideal solution is a spatial measurement of
water heights from a remote platform.
100 Inundated!
Existing technology requires flow through a
channel and provides discharge at a singular
cross-section.
L. Hess photos
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Lack of Global Discharge
It is impossible to measure discharge along these
Arctic braided rivers with a single gauging
station. Like the Amazon floodplain, a network
of gauges located throughout a braided river
reach is impractical. Instead, a spatial
measurement of flow from a remote platform is
preferred.
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Globally Declining Gauge Network

• Many of the countries whose hydrological
  networks are in the worst condition are those
  with the most pressing water needs. A 1991 United
  Nations survey of hydrological monitoring
  networks showed "serious shortcomings" in
  sub-Saharan Africa, says Rodda. "Many stations
  are still there on paper," says Arthur Askew,
  director of hydrology and water resources at the
  World Meteorological Organization (WMO) in
  Geneva, "but in reality they don't exist." Even
  when they do, countries lack resources for
  maintenance. Zimbabwe has two vehicles for
  maintaining hydrological stations throughout the
  entire country, and Zambia just has one, says
  Rodda.
• Operational river discharge monitoring is
  declining in both North America and Eurasia.
  This problem is especially severe in the Far East
  of Siberia and the province of Ontario, where 73
  and 67 of river gauges were closed between 1986
  and 1999, respectively. These reductions will
  greatly affect our ability to study variations in
  and alterations to the pan-Arctic hydrological
  cycle.

Stokstad, E., Scarcity of Rain, Stream Gages
Threatens Forecasts, Science, 285, 1199,
1999. Shiklomanov, A.I., R.B. Lammers, and C.J.
Vörösmarty, Widespread decline in hydrological
monitoring threatens Pan-Arctic research, EOS,
83, 13-16, 2002.
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Science Questions

• How does this lack of measurements limit our
  ability to predict the land surface branch of the
  global hydrologic cycle?
• Stream flow is the spatial and temporal
  integrator of hydrological processes thus is used
  to verify GCM predicted surface water balances.
• Unfortunately, model runoff predictions are not
  in agreement with observed stream flow.

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Model Predicted Discharge vs. Observed
Observed does not match any model
REAN2 NCEP/DOE AMIP Reanalysis II GSM, RSM
NCEP Global and Regional Spectral Models ETA
NCEP Operational forecast model OBS Observed

• Mouth of Mississippi both timing and magnitude
  errors (typical of many locations).
• Within basin errors exceed 100 thus gauge at
  mouth approach will not suffice.
• Similar results found in global basins

Roads et al., GCIP Water and Energy Budget
Synthesis (WEBS), J. Geophysical Research, in
press 2003. Lenters, J.D., M.T. Coe, and J.A.
Foley, Surface water balance of the continental
United States, 1963-1995 Regional evaluation of
a terrestrial biosphere model and the NCEP/NCAR
reanalysis, J. Geophysical Research, 105,
22393-22425, 2000. Coe, M.T., Modeling
terrestrial hydrological systems at the
continental scale Testing the accuracy of an
atmospheric GCM, J. of Climate, 13, 686-704, 2000.
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Resulting Science Questions

• What is the role of wetland, lake, and river
  water storage as a regulator of biogeochemical
  cycles, such as carbon and nutrients?
• Rivers outgas as well as transport C. Ignoring
  water borne C fluxes, favoring land-atmosphere
  only, yields overestimates of terrestrial C
  accumulation
• Water Area x CO2 Evasion Basin Wide CO2 Evasion

(L. Hess photos)
Richey, J.E., J.M. Melack, A.K. Aufdenkampe, V.M.
Ballester, and L.L. Hess, Outgassing from
Amazonian rivers and wetlands as a large tropical
source of atmospheric CO2, Nature, 416, 617-620,
2002.
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Global Wetlands

• Wetlands are distributed globally, 4 of Earths
  land surface
• Current knowledge of wetlands extent is inadequate

• Amazon wetlands are much larger (2x) than thought
  in this view Melack et al, in review
• Putuligayuk River watershed on the Alaskan north
  slope studies with increasing resolution
  demonstrate a greater open water area (2 vs.
  20 1km vs. 50m) and as much as 2/3 of the
  watershed is seasonally flooded tundra Bowling
  et al., WRR in press.

Matthews, E. and I. Fung, Methane emission from
natural wetlands global distribution, area, and
environmental characteristics of sources, Global
Biochemical Cycles, v. 1, pp. 61-86, 1987.
Prigent, C., E. Matthews, F. Aires, and W.
Rossow, Remote sensing of global wetland dynamics
with multiple satellite data sets, Geophysical
Research Letters, 28, 4631-4634, 2001.
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Societal Questions
For 2025, Relative to 1985

• Lacking measurements of water discharge and
  storage change, what are the implications for
  global water management?
• Ability to globally forecast freshwater
  availability is critical for population
  sustainability.
• Water use changes due to population are more
  significant than climate change impacts.
• Predictions also demonstrate the complications to
  simple runoff predictions that ignore human water
  usage (e.g., irrigation).

Vörösmarty, C.J., P. Green, J. Salisbury, and
R.B. Lammers, Global water resources
Vulnerability from climate change and population
growth, Science, 289, 284-288, 2000.
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Societal Questions

• What is the hydrology of flooding in urban and
  agricultural areas?
• Flooding imposes clear dangers, but the lack of
  water heights during the passage of the flood
  wave and the lack of contemporaneous inundation
  mapping limit important hydraulic modeling that
  would otherwise predict the zones of impact.

U.S.
China
Europe
India
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Science Questions from the Research Strategy
Variability
Forcing
Response
Consequence
Prediction
Precipitation, evaporation cycling of water
changing?
Atmospheric constituents solar radiation on
climate?
Clouds surface hydrological processes on
climate?
Weather variation related to climate variation
(floods)?
Weather forecasting improvement?
Ecosystem responses affects on global carbon
cycle?
Global ocean circulation varying?
Changes in land cover land use?
Consequences in land cover land use?
Transient climate variations?
Surface transformation?
Changes in global ocean circulation?
Coastal region change?
Trends in long-term climate?
Global ecosystems changing?
Stratospheric ozone changing?
Stratospheric trace constituent responses?
Future atmospheric chemical impacts?
Ice cover mass changing?
Sea level affected by climate change?
Future concentrations of carbon dioxide and
methane?
Motions of Earth interior processes?
Pollution effects?
YellowPrimary BlueSecondary
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ESE Questions that an ESSP Mission Would Address

• KEY How are global precipitation, evaporation,
  and the cycling of water changing? How are
  global ecosystems changing? (variability)
• Global water cycle models require mass and flux
  balances from Q and DS
• Inundation area provides CO2, CH4 exchange with
  the atmosphere, and seasonal variations in C
• Global measurements of Q and DS provide for the
  management of fresh water resources
• What changes are occurring in global land cover
  and land use, and what are their causes? How is
  the earth's surface being transformed? (forcing)
• Floods significantly alter the land surface
  whereas their cause is linked, in part, to within
  catchment changes in land cover and land use
• KEY What are the effects of clouds and surface
  hydrologic processes on Earths climate? How do
  ecosystems and biogeochemical cycles respond to
  and affect global environmental change?
  (response)
• Wetlands, reservoirs, lakes all provide
  significant areas for evaporation and direct
  reception of precipitation these need to be
  fully incorporated in GCMs
• CO2, CH4 evasion from the water surface, and
  their fluvial transport are important components
  in the C-balance of wetland ecosystems
• How are variations in local weather,
  precipitation and water resources related to
  global climate variation? (consequences)
• Real time observations of Q and DS provide
  constraints on flood waves (e.g., flooded area,
  wave velocity) resulting from local to regional
  storms what is the global distribution of these
  in connection to climate oscillations (e.g.,
  ENSO)?
• How well can transient climate variations be
  understood and predicted? (prediction)
• Potential of assimilating Q and DS in global
  water cycle and climate models will allow past
  response to weather and climate for predicting
  future scenarios.

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Why Use Satellite Based Observations Instead of
More Stream Gauges?

• Wetlands and floodplains have non-channelized
  flow, are geomorphically diverse at a point
  cross-sectional gauge methods will NOT provide
  necessary Q and ?S.
• Wetlands are globally distributed (cover 4
  Earths land 1gauge/1000 km2 X 60,000 350M,
  too expensive)
• Declining gauge numbers makes the problem only
  worse. Political and Economic problems are real
  and insurmountable.
• Need a global dataset of Q and ?S contemporaneous
  with other NASA hydrologic missions (e.g., soil
  moisture, precipitation). Q ?S verify global
  hydrologic models.
• Remote sensing offers the potential for obtaining
  a different kind of data (e.g. dynamics of
  surface water spatial variations) and should not
  be viewed as simply a gage replacement strategy

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Potential ESSP Solutions
Topex/POSEIDON
Balbina Reservoir, Amazon

• Wetlands Floodplains We need storage change
  measurements which will likely be measured using
  altimetry and imagery
• To match ESSP costs, this might be achieved with
  an altimeter following the same orbit as ALOS
  (NASDAs L-band SAR) or using an onboard,
  low-cost optical camera.
• This is the most technology ready method of
  measuring surface water storage at a high spatial
  resolution.
• River Channels We need discharge which requires
  river water height, water velocity, and channel
  cross-section.
• Measuring flow velocities from space (e.g.,
  along-track interferometric SAR) is too costly.
  Instead, water slope can be easily converted to
  velocity using Mannings equation, thus an
  altimeter in a rapid repeat cycle (7 days?)
  could provide river slope for slow moving
  floodwaves. Cross sections would be measured
  during lowest-flow conditions.

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ESSP Mission

• Science Team
• Doug Alsdorf, Paul Houser, Yunjin Kim, Dennis
  Lettenmaier, Ernesto Rodgriguez, Charles
  Vörösmarty.
• Costs?
• A radar altimeter is almost certainly required
  and should be fundable within ESSP the cost cap.
  Additional imagery may push the costs too high,
  but could be alleviated with a low-cost onboard
  optical camera or using an orbit that matches
  existing SARs.
• Partnerships?
• International The Surface Water Working Group
  has already contacted ESA and NASDA personnel and
  response has been very positive.
• Domestic the USGS and US Bureau of Reclamation
  actively participate in the working group NSF
  has a very strong interest in hydrology
  (www.CUAHSI.org)
• Two Primary Concerns
• The science for a surface water mission is well
  founded, but the technology funding needs to be
  assured. We need to ensure that NASA HQ supports
  technology development via ESTOs IIP.
• The spatial and temporal resolutions for
  measuring surface water elevations and extents,
  which are necessary for answering the science and
  societal questions are not well established.
  Thus, we plan a virtual mission which is a data
  assimilation of existing sensors operating at
  various spatial and temporal scales. We'll use
  existing sensors to determine the accuracy of
  what we know now (i.e., inundation areas from
  imaging methods and water surface heights from
  altimeters), compare results to in-situ
  measurements and determine what we need to know
  using a global water-cycle model. This effort
  will be used to constrain the temporal and
  spatial samplings necessary but the coupling with
  a water cycle model will allow us to more
  completely understand the hydrologic impacts of
  knowing or not knowing surface water values in
  any given area.

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Conclusions

• Lack of Q and ?S measurements cannot be
  alleviated with more gauges (e.g., wetlands
  diffusive flow).
• This lack leads to a poor basis for evaluation of
  global hydrologic and climate model predictions
  (and perhaps eventually assimilation of direct
  measurements of a key flux and state variable in
  the water balance).
• Ideal solution is a satellite mission capable of
  measureing river discharge and surface extent,
  and lake, reservoir, and wetland storage change.
• International partnerships are highly desirable,
  and perhaps essential, to move a community agenda
  forward

www.swa.com/hydrawg/