October 2003 Meeting at NASA GSFC ESSP Powerpoint PresentationPresentation Transcript
Preliminary Concepts for a Surface Water ESSP Satellite Mission ESSP Presentation at GSFC October 8, 2003 Funded by NASA Terrestrial Hydrology Program www.swa.com/hydrawg/ P. Houser, D. Lettenmaier, D. Alsdorf
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 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 .
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.
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 Models ETA: NCEP Operational forecast model OBS: Observed Observed does not match any model Runoff (mm/day) 1.25 1.00 0.75 0.50 0.25 0.00 OBS REAN2 RSM ETA GSM J F M A M J J A S O N D
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 CO 2 Evasion = Basin Wide CO 2 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)
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].
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.
Science Questions from the Research Strategy 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? Yellow=Primary Blue=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 CO 2 , CH 4 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
CO 2 , CH 4 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 Δ S.
Wetlands are globally distributed (cover ~4% Earth’s land; 1gauge/1000 km 2 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 Δ S contemporaneous with other NASA hydrologic missions (e.g., soil moisture, precipitation). Q & Δ 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
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.
Topex/POSEIDON Balbina Reservoir, Amazon
Doug Alsdorf, Paul Houser, Yunjin Kim, Dennis Lettenmaier, Ernesto Rodgriguez, Charles V ö r ö smarty.
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.
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.
Lack of Q and Δ 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