AGU 2002 Presentation

Information about AGU 2002 Presentation

Published on January 3, 2008

Author: Garrick

Source: authorstream.com

Content

The NASA Working Group on River and Wetland Hydrologic Processes :  The NASA Working Group on River and Wetland Hydrologic Processes D. Alsdorf, G.D. Emmitt, D. Lettenmaier, L. Smith, C. Vörösmarty Funded by the Terrestrial Hydrology Program at NASA: Jared Entin, Program Manager Working Group Participants::  Working Group Participants: Charon Birkett, David Bjerklie, Bob Brakenridge, John Costa, Melba Crawford, Cassiano D'Almeida, Lawrence Dingman, Jay Famiglietti, Balazs Fekete, Randall Friedly, Steve Hamilton, Dave Harding, Laura Hess, William Heaps, Paul Houser, David Imel, Mike Jasinski, Yunjin Kim, William Kirby, Victor Koren, Pascal Kosuth, Venkataraman Lakshmi, Soren Madsen, Mahta Moghaddam, Delwyn Moller, Pierre Morel, Dan O'Connell, Keith Raney, Ernesto Rodriguez, Ali Safaeinili, Gary Spiers, Eric Wood, Thomas Yorke You are invited to join us! My apologies if I have forgotten you, please let me know! Outline:  Outline A Brief History of the Working Group The Lack of Discharge and Water Storage Change Measurements Resulting Science Questions Why Satellite Based Observations Are Required to Answer These Questions Potential Spaceborne Solutions Your Participation is Welcomed Amazon Floodplain (L. Hess photo) www.swa.com/hydrawg/ History of the Working Group:  History of the Working Group Outgrowth of the NASA ESE post-2002 Mission Planning process & from our “White Paper” – see our www. One of three THP working groups (Soil Moisture, Tom Jackson; and Cold Land Processes, Don Cline) Four working group meetings (Aug 2000; May 2001; Dec 2001; Nov 2002) and the fifth will be in Spring 2003. Funding for two more years from NASA Terrestrial Hydrology Program; based on renewal proposal – see our www. Are now planning for Field Program www.swa.com/hydrawg/ Lack of Q?:  Lack of Q? Keep these measuring approaches in mind Lack of Q and ΔS Measurements: An example from Inundated Amazon Floodplain:  Lack of Q and ΔS Measurements: An example from Inundated Amazon Floodplain 100% Inundated! Singular gauges are incapable of measuring the flow conditions and related storage changes in these photos whereas complete gauge networks are cost prohibitive. The ideal solution is a spatial measurement of water heights from a remote platform. How does water flow through these environments? (L. Mertes, L. Hess photos) Example: Braided Rivers:  Example: Braided Rivers 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:  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 Transactions of AGU, 83, 13-16, 2002. Resulting Science Questions:  Resulting 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:  Model Predicted Discharge vs. Observed Central U.S., both timing and magnitude errors (typical of many locations). Within basin errors exceed 100%; thus gauge at mouth approach will not suffice. Annual predictions ~may~ be reasonable, but seasonal are not. Similar results found in global basins. 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. Terrestrial-Biosphere Model, “IBIS” forced with daily climate inputs from NCEP or with observed Precipitation. Resulting Science Questions:  Resulting Science Questions What are the implications for global water management and assessment? 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 Resulting Science Questions:  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) CO2 Evasion in the Amazon:  CO2 Evasion in the Amazon Over 300,000 km2 inundated area, 1800+ samples of CO2 partial pressures, 10 year time series, and an evasion flux model Results: 470 Tg C/yr all Basin; 13 x more C by outgassing than by discharge But what are seasonal and global variations? If extrapolate Amazon case to global wetlands, = 0.9 Gt C/yr, 3x larger than previous global estimates; Tropics are in balance, not a C Sink? 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. Why Use Satellite Based Observations Instead of More Stream Gauges?:  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 $40,000 = $ 230M) Declining gauge numbers makes the problem only worse. Political and Economic problems are real. Need a global dataset of Q and ΔS concomitant with other NASA hydrologic missions (e.g., soil moisture, precipitation). Q & ΔS verify global hydrologic models. Solutions from Radar Altimetry:  Solutions from Radar Altimetry Birkett, C.M., Contribution of the TOPEX NASA radar altimeter to the global monitoring of large rivers and wetlands, Water Resources Res.,1223-1239, 1998. Birkett, C.M., L.A.K. Mertes, T. Dunne, M.H. Costa, and M.J. Jasinski, Surface water dynamics in the Amazon Basin: Application of satellite radar altimetry, accepted to Journal of Geophysical Research, 2002. Water surface heights, relative to a common datum, derived from Topex/POSEIDON radar altimetry. Accuracy of each height is about the size of the symbol. Topex/POSEIDON tracks crossing the Amazon Basin. Circles indicate locations of water level changes measured by T/P radar altimetry over rivers and wetlands. Presently, altimeters are configured for oceanographic applications, thus lacking the spatial resolution that may be possible for rivers and wetlands. Solutions from Interferometric SAR for Water Level Changes:  Solutions from Interferometric SAR for Water Level Changes Alsdorf, D.E., J. M. Melack, T. Dunne, L.A.K. Mertes, L.L. Hess, and L.C. Smith, Interferometric radar measurements of water level changes on the Amazon floodplain, Nature, 404, 174-177, 2000. Alsdorf, D., C. Birkett, T. Dunne, J. Melack, and L. Hess, Water level changes in a large Amazon lake measured with spaceborne radar interferometry and altimetry, Geophysical Research Letters, 28, 2671-2674, 2001. JERS-1 Interferogram spanning February 14 – March 30, 1997. “A” marks locations of T/P altimetry profile. Water level changes across an entire lake have been measured (i.e., the yellow marks the lake surface, blue indicates land). BUT, method requires inundated vegetation for “double-bounce” travel path of radar pulse. These water level changes, 12 +/- 2 cm, agree with T/P, 21 +/- 10++ cm. Conclusions::  Conclusions: Lack of Q and ΔS measurements cannot be alleviated with more gauges (e.g., wetlands = diffusive flow). This lack leads to poorly constrained global hydrologic models. Ideal solution is a satellite mission with temporal and spatial resolutions compatible with planned missions and modeling efforts. www.swa.com/hydrawg/

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