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INTEGRATED OBSERVATIONS OF SEMI-ARID LAND-SURFACE-ATMOSPHERE
INTERACTIONS: POSTER SESSION OVERVIEW B.F. Goff* and D.C. Goodrich USDA-Agricultural Research Service, Tucson, AZ, USA. *Corresponding author: Bruce F. Goff, USDA-ARS Southwest Watershed Research Center 2000 E. Allen Road, Tucson, AZ 85719, USA; email: bgoff@tucson.ars.ag.gov
1. INTRODUCTION
Semi-arid regions cover almost one-fifth of the world's land surface and are significant sources of food, fiber, habitat, and open space. They are important components of the global land-surface-atmosphere system, interacting with other components to influence global circulation patterns while simultaneously being affected by those patterns. Because of the complex and interdependent nature of global systems, global change research requires an integrated approach to observing land-surface-atmosphere interactions. The benefit of this approach is demonstrated in the many oral and poster presentations given as part of this Symposium. The purpose of this paper is to briefly highlight some of the major research themes occurring in the poster presentations in order to direct readers to posters and authors of particular interest
2. RESEARCH THEMES
For the purposes of this paper, poster presentations have been categorized according to 1) principal hydrometeorological process, 2) research approach, 3) principal measurement technique, 4) vegetation type, and 5) program or institutional affiliation. A summary of poster themes is presented in Table 1. A brief discussion of the themes is presented below. Note that all references cited here appear as poster presentations or papers within these Symposium Proceedings. Consequently, only the authors' names and presentation titles are provided.
2.1 Hydrometeorological Process
Surface fluxes (energy and water), evapotranspiration (ET), and plant transpiration are the principal hydrometeorological processes addressed in the poster presentations (e.g., Chehbouni et al. a & b, and Schaeffer and Williams). They represent interrelated components of the overall energy and water balance, and are differentiated here simply to indicate research emphasis. Subsidiary research on water source, stream-aquifer interactions, soil moisture, and plant growth was typically conducted to support these energy and water balance studies (e.g., Snyder et al., Mac Nish et al., Moran et al., and Nouvellon et al.). Most of these studies are part of larger global change research programs in the USA and Mexico. Notable exceptions are the work of Venencio and Garcia on droughts in Argentina, and the results presented by Gay a & b and others on the long-term ET inventory program in Arizona.
2.2 Research Approach
Research approach was categorized as either hydrometeorological or ecophysiological. Most investigators took a hydrometeorological approach to the research (e.g., Prueger et al., Whitaker et al.), that is, the emphasis was on the physical characteristics of the land-surface-atmosphere system rather than the ecological or biological characteristics. However, where the fundamental research question was ecological in nature rather than physical, an ecophysiological approach was used. This was the case for the water source research of Snyder et al., the sap flux research of Schaeffer and Williams, and the modeling work of Bégué et al. and Nouvellon et al.
2.3 Measurement Technique
For field experiments, researchers used a variety of standard atmospheric, hydrologic, and soil sensors and measuring devices to make direct measurements of hydrometeorological variables (e.g., Mac Nish et al., Scott et al.).
Table 1. Summary of poster presentation themes, session on Integrated Observations of Semi-Arid Land-Surface- Atmosphere Interactions.
Authors* Hydrometeor- ological Process Research Approach Measurement Technique Vegetation Type Program Affiliation Bégué et al. surface fluxes ecophysio. modeling grassland SALSA Chehbouni et al. (a) surface fluxes hydromet. remote sensing grass/shrub steppe SALSA Chehbouni et al. (b) surface fluxes hydromet. remote sensing grass/shrub steppe SALSA Eichinger et al. surface fluxes hydromet. remote sensing riparian SALSA Gay (a) ET hydromet. direct irrigated crop AZET Gay (b) ET hydromet. direct riparian/orchard AZET Goff and Goodrich ET hydromet. direct riparian SALSA Goodrich et al. ET hydromet. various riparian SALSA Harlow et al. surface fluxes hydromet. modeling mixed SALSA Honaman et al. ET, PET hydromet. direct irrig. crop/shrub AZET Hymer et al. soil moisture hydromet. direct shrub steppe SALSA Konrad et al. ET hydromet. modeling irrigated crop AZET LeMone et al. surface fluxes hydromet. direct mixed CASES-97 Lhomme et al. transpiration hydromet. modeling grass/shrub steppe SALSA Mac Nish et al. stream-aquifer hydromet. direct riparian SALSA Moran et al. soil moisture hydromet. remote sensing grass/shrub steppe SALSA Nouvellon et al. plant growth ecophysio. modeling grassland SALSA Pan et al. ET hydromet. modeling mixed ISU Prueger et al. surface fluxes hydromet. direct grass/shrub steppe JER Richardson et al. ET hydromet. direct irrigated crop AZET Schaeffer and Williams transpiration ecophysio. direct riparian SALSA Scott et al. ET hydromet. direct grass/shrub steppe SALSA Snyder et al. water source ecophysio. direct (isotopes) riparian SALSA Venencio and Garcia drought hydromet. modeling grass/shrub steppe UNL Watts et al. surface fluxes hydromet. remote sensing grass/shrub steppe SALSA Whitaker et al. stream-aquifer hydromet. direct riparian SALSA Yucel et al. surface fluxes hydromet. remote sensing mixed SALSA
* See references list for citation. (Note: some poster presentations may not have a paper in this issue).Others employed remote sensing technology to make indirect measurements of these variables. Remote sensing data were usually supplemented by direct measurements. The remote sensing techniques included satellite, aircraft, and ground-based radiometry, (Moran et al., Watts et al., Yucel et al.), lidar (Eichinger et al.), and scintillometry (Chehbouni et al. a & b, Watts et al.). In addition, a few studies employed computer modeling combined with existing data sets to simulate interaction among hydrometeorological processes. These include the modeling of grassland function (Bégué et al., Lhomme et al., and Nouvellon et al.), surface fluxes and ET (Harlow et al. and Konrad et al., Pan et al.), and drought (Venencio and Garcia).
2.4 Vegetation Type
Grasslands and shrub steppe represent the most extensive vegetation types examined in the poster studies. (e.g., Bégué et al., Hymer et al., Moran et al, Nouvellon et al., Prueger et al., Scott et al., Venencio and Garcia, Watts et al.). The riparian vegetation along the San Pedro River in SE Arizona and NE Sonora is an inclusion within the grassland and shrub steppe vegetation types. Riparian vegetation is highly susceptible to natural or human induced changes in the hydrologic regime. Consequently, several poster presentations focus on this critical issue (e.g., Goodrich et al., Mac Nish et al., Schaeffer and Williams, Snyder et al., Whitaker et al.). Other investigators examined ET from irrigated crops and natural vegetation in central and southern Arizona (Gay a & b, Honaman et al., Konrad et al., Richardson et al.). Studies listed as having a "mixed" vegetation type were typically those of a regional or continental nature.
2.5 Program Affiliation
The majority of studies summarized here were done as part of the Semi-Arid Land-Surface-Atmosphere (SALSA) Program, a multi-agency global change research effort led by the USDA Agricultural Research Service (e.g., Goff and Goodrich, Goodrich et al.). Similarly, the study by LeMone et al. was part of the CASES-97 global change research effort in SE Kansas and the work of Prueger et al. was part of the JORNEX campaign in New Mexico. Several other poster presentations describe results of the AZET program, a long-term ET inventory program of the Arizona Agricultural Experiment Station.
3. CONCLUDING REMARKS
This paper briefly summarized some of the important research themes discussed in the poster presentations of the Integrated Observations of Semi-Arid Land-Surface-Atmosphere Interactions session of this Symposium. It is hoped that this review will give readers a broader perspective of the breadth and depth of hydrometeorological research being conducted in semi-arid lands, and promote future cooperation in this kind of integrated research.
4. ACKNOWLEDGMENTS
Financial support from the USDA-ARS Global Change Research Program and NASA grant W-18,997 is gratefully acknowledged.
5. REFERENCES
All references are those of poster presentations or papers appearing in this issue.
Bégué, A., D. Luquet, J. Dauzat, Y. Nouvellon, and H. Rey. Vegetation hemispherical fluxes calculated from 3D computerized vegetation canopies and ray tracing technique: application to a semi-arid grassland.
Chehbouni, A., J. Qi, T. Clarke, D. Luquet, Y. Nouvellon, G. Boulet, G. Dedieu, and Y. Kerr. (a) Simultaneous examination of view and sun angles effect on visible, NIR and TIR measurements over semi-arid grassland.
Chehbouni, A., R. Scott, O. Hartogensis, J-P. Lhomme, D.C. Goodrich, Y. Kerr, and H. De Bruin. (b) Examination of the relationship between radiative and aerodynamic surface temperature over heterogeneous surfaces.
Eichinger, W.E., S. Krishnamoorthy, L. Chen, D. Cooper, and L. Hipps. The effects of surface heterogeneity on the measurement of surface fluxes.
Gay, L.W. (a) Evapotranspiration extremes for irrigated alfalfa in the Arizona desert.
Gay, L.W. (b) Record rates of evapotranspiration from moist-site forest ecosystems in the Arizona desert.
Goff, B.F., and D.C. Goodrich. Think globally, act locally: community participation in "SALSA" global change research.
Goodrich, D.C., J. Qi, M.S. Moran, R. Scott, D. Williams, S. Schaeffer, R. Mac Nish, T. Maddock, B.F. Goff, J. Toth, L. Hipps, D. Cooper, J. Schieldge, A. Chehbouni, C. Watts, J. Shuttleworth, O. Hartogensis, H. De Bruin, Y. Kerr, C. Unkrich, R. Marsett, W. Ni. Seasonal estimates of riparian vegetation evapotranspiration (consumptive water use) using remote and in-situ measurements.
Harlow, C., J. Toth, and J. Shuttleworth. Evaluation of the SiB2 surface scheme in a semi-arid region.
Honaman, A.M., L.W. Gay, and A. Matthias. Predicting actual evapotranspiration from irrigated alfalfa using desert climate data and Penman's combination model.
Hymer, D.C., M.S. Moran, and T. Keefer. Monitoring temporal soil moisture variability with depth using calibrated in-situ sensors.
Konrad, Sara L., L.W. Gay, and P. Brown Temporal and spatial variability of evapotranspiration from irrigated alfalfa in the Arizona desert.
LeMone, M.A., R. Grossman, B. Hicks, T. Horst, J. Lundquist, B. McMillen, S. Oncley, and R.Qualls. Factors affecting the diurnal variation of wind, temperature, and moisture over a mesoscale watershed--preliminary results from CASES97.
Lhomme, J-P., A. Chehbouni, E. Elguero, and G. Boulet. Examination of Monteith's parameterization of canopy conductance.
Mac Nish, R.D., C.J. Peters, M.A. Schulte, D.C. Goodrich, D.R. Pool, T. Maddock III, C. Unkrich, M.P.L. Whitaker, and B.F. Goff. Quantification of groundwater - surface water interactions in a southwestern riparian system.
Moran, M.S., D. Hymer, J. Qi, E. Sano, R. Marsett, M. Helfert, and W. Ni. Soil moisture evaluation using synthetic aperture radar (SAR) in semi-arid rangeland.
Nouvellon, Y., S. Rambal, A. Bégué, M.S. Moran, J-P. Lhomme, J. Qi, A. Chehbouni, and D. Lo Seen. An ecophysiological model for grasslands..
Pan, Z., E. Takle, M. Segal, and J. Brown On relative efficiency of horizontal moisture flux and evapotranspiration.
Prueger, J. H., W. Kustas, L. Hipps, and J. Hatfield. Surface energy partitioning over black grama and mesquite dune biomes in a northern Chihuahuan desert.
Richardson, J.C., L.W. Gay, and A. Matthias. Measuring winter wheat with an "aero/energy balance" model.
Schaeffer, S.M., and D. G. Williams. Transpiration of desert riparian forest canopies estimated from sap flux.
Scott, R.L., J. Shuttleworth, and D.C. Goodrich. Water use of two dominant riparian vegetation communities in southeastern Arizona.
Snyder, K. A., D. Williams, and V. Gempko. Water source determination for cottonwood, willow and mesquite in riparian forest stands.
Venencio, M.A., and N. Garcia. On the droughts in the "Pampa Humeda" (Argentina) and its relations with alternative water resources.
Watts, W., A. Chehbouni, Y. Kerr, H.A.R. deBruin, O. Hartogensis, J. Rodriguez, and A. Garibay. Comparison of sensible heat flux estimates using AVHRR with scintillometer measurements over grass and mesquite in northwest Mexico.
Whitaker, M.P.L., T. Maddock, B. Mac Nish, D.C. Goodrich, and B.F. Goff. Monitoring bank storage in the San Pedro riparian national conservation area, Arizona.
Yucel I., J. Garatuza-Payan, J. Toth, J. Shuttleworth, and R. Pinker. Cloud screened surface radiation estimates with high resolution from GOES-9 data.
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