Preliminary Concepts for a Surface Water ESSP Satellite Mission

ESSP Presentation at GSFCOctober 8, 2003

Funded by NASA Terrestrial Hydrology Program

www.swa.com/hydrawg/

P. Houser,

D. Lettenmaier, D. Alsdorf

Outline

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

Amazon Floodplain (L. Hess photo)

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.

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!

L. Hess photos

Existing technology requires flow through a channel and provides discharge at a singular cross-section.

Lack of Global DischargeIt 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.

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.

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.

Model Predicted Discharge vs. 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.

REAN2: NCEP/DOE AMIP Reanalysis II GSM, RSM: NCEP Global and Regional Spectral ModelsETA: NCEP Operational forecast modelOBS: Observed

Runoff (mm/day)1.251.000.750.500.250.00

OBS REAN2 RSM ETAGSM

J F M A M J J A S O N D

Observed does not match any model

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

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.

(L. Hess photos)

Global Wetlands

Wetlands are distributed globally, ~4% of Earth’s land surface

Current knowledge of wetlands extent is inadequate

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.

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].

Societal Questions

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.

For 2025, Relative to 1985

Societal Questions

U.S.

China

India

Europe

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.

Variability Forcing Response Consequence Prediction

Precipitation, evaporation &

cycling of water changing?

Global ocean circulation

varying?

Global ecosystems changing?

Stratospheric ozone changing?

Ice cover mass changing?

Motions of Earth & interior

processes?

Atmospheric constituents &

solar radiation on climate?

Changes in land cover & land use?

Surface transformation?

Clouds & surface hydrological processes on

climate?

Ecosystem responses &

affects on global carbon cycle?

Changes in global ocean circulation?

Stratospheric trace constituent

responses?

Sea level affected by climate

change?

Pollution effects?

Weather variation related to climate variation

(floods)?

Consequences in land cover & land use?

Coastal region change?

Weather forecasting

improvement?

Transient climate

variations?

Trends in long-term climate?

Future atmospheric

chemical impacts?

Future concentrations of

carbon dioxide and methane?

Science Questions from the Research Strategy

Yellow=PrimaryBlue=Secondary

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 ∆S Inundation area provides CO2, CH4 exchange with the atmosphere, and seasonal variations in C

Global measurements of Q and ∆S 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 Earth’s 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 ∆S 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 ∆S in global water cycle and climate models will allow past response to

weather and climate for predicting future scenarios.

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 ΔS.

Wetlands are globally distributed (cover ~4% Earth’s 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 ΔS contemporaneous with other NASA hydrologic missions (e.g., soil moisture, precipitation). Q & ΔS 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

Topex/POSEIDON

Potential ESSP Solutions

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 (NASDA’s 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 Manning’s 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.

Balbina Reservoir, Amazon

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 ESTO’s 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.

Conclusions: Lack of Q and ΔS 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

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