PC-03 Group Augmented Abstract

Influence of Land Surface Processes/Land Cover Changes
in Amazon on Regional Hydrometeorology

Principal Investigator: Yongkang Xue (UMCP)
Co-Investigator: Chou Sin Chan (CPTEC)
Co-Investigator: Steve Prince (UMCP)
Co-Investigator: Y.C. Sud (NASA GSFC)
Co-Investigator: Clemente A. Tanajura (CPTEC)
Co-Investigator: Javier Tomasella (CPTEC)
Co-Investigator: Xiwu Zhan (UMCP)
Collaborator: Dr. James Collatz (NASA)
Collaborator: Dr. David Fitzjarrald (SUNY)

 

1) The general goals

In this project, we propose to use the regional Eta model coupled with a biosphere model, SSiB, to investigate hydrometeorological prediction in the Amazon Basin at seasonal to interannual time scales and the effects of deforestation on circulation and rainfall, in particular, the annual cycle of convective activity. The land cover and the soil properties will be specified using remotely sensed data and derived data based upon observations, respectively. Several important parameterizations, including soil hydrology, stomatal resistance, and convective processes, will be investigated to elucidate the mechanisms of land-atmosphere interactions in South America and evaluate the sensitivity and uncertainty of these interactions in model simulations. The observational data from LBA will be applied to these studies. The ultimate goal is to improve the hydrometeorological prediction in the LBA region by improving the land surface components in a coupled regional model.

In our research efforts, the prediction of rainfall in the Amazon Basin will be a major focus. The spatial and temporal distribution of precipitation in the Amazon Basin largely depends on convective activity. In a recent study, Zhou and Lau (1998) infer that the austral spring, summer, and fall rainfall activity in South America has characteristic features of a monsoon climate system. Our main focus in this proposal is on seasonal-to-interannual prediction, especially prediction of this annual convective activity, and its relation to land surface processes.
 

2). Models and predictions for this study

The NCEP Eta regional model will be used for this study. In a recent study, conducted with a later version of the Eta/bucket model by Dr. Chou(Co-I) and her colleagues at the Center for Weather Prediction and Climate studies (CPTEC), a one-month forecast was performed for November 1997. The general pattern of the forecast precipitation is comparable with the observations, however a dry bias can be identified over Northeast Brazil and the Northern coast (Figure 1). A coupled Eta/SSiB model (Xue et al., 1996) will be used for LBA study. Figure 2 is the South American vegetation map for Eta/SSiB.

In this proposal, we will use Eta/SSIB to conduct 12 month integrations with climatological sea surface temperature (SST) data as surface boundary conditions over the ocean. The role of land surface processes in simulating the annual hydrologic cycle will be investigated. The El Nino and La Nina have substantial impact on South American precipitation. After the completion of the above- mentioned integrations, SSTs from a typical El Nino year and a typical La Nina year will be used as the boundary conditions for additional integrations. During the LBA, measurements will be taken at different scales. These data will allow the establishment of a profile of the vertical structure of the troposphere inclusive at canopy levels. The model will be validated against the observations and analyses.
 

3). Impact of land cover/land cover change on the South American hydroclimatology

Amazon is the largest continuous region of tropical rainforest in the world, and a large amount of the original tropical forest has been lost to deforestation. Sensitivity study has shown it may have substantial impact on regional climate (e,g,, Xue et al., 1996a). With satellite remote sensing data, the scales and locations of Amazonian deforestation have been quantified and assessed with reasonable accuracy. Using these remote sensing assessments instead of the hypothetical estimates of the deforestation, the GCM studies on the hydrometeorological impacts of deforestation will be more realistic.

In this study, satellite data will be used for experimental designs in deforestation scenarios. Data from Thematic Mapper (TM) and Multispectral Scanner System (MSS) of Landsat are being used to create land use and deforestation maps for the tropical areas for the 1970s, the 1980s, and the 1990s. For the deforestation maps, the project has further aggregated the fine scale maps into 16km grid maps. Using these land cover/land cover change maps, we will investigate the methodology to implement land cover change detection product and how does the land cover change affect the regional hydrometeorological conditions in South America.
 

4). Sensitivity of model simulations to parameterizations in the hydrologic processes

In this project, several important parameterizations crucial to the hydrologic cycle will be tested, which include soil hydrology, stomatal resistance, and convective scheme. The observational data from LBA will be used for these studies. The goal is to elucidate the mechanisms of climate change in South America and evaluate the sensitivity and uncertainty of these interactions in model simulations.
 

4.1. Soil properties

In the Amazon area, there is a wide variety of soil types. The Radambrasil project (1973-1986) has surveyed and mapped soil types, and produced 1162 soil profiles to a depth of 2m. Tomasella & Hodnett (1998) derived and tested a PTF using soil data of the Brazilian Amazonia and related the estimations to the Brooks & Corey (1964) retention parameters. In this project, we will create an Amazon soil map for the Eta and the GCM based on Radambrasil's soil tables up to 2 meters. This soil map will be used for model integration and its results will be compared with those from current SSiB soil map in the regional model. We will conduct another experiment, in which the Tomasella and Hodnett parameterizations are used for the soil. These three tests will provide information regarding the sensitivity of land-atmosphere interaction to soil processes and improve the specification of soil condition in the models.
 

4.2 Parameterizations of stomatal resistance

Stomatal resistance affects the energy partitioning between the latent heat flux and the sensible heat flux. It is a crucial component of biosphere models. We plan to introduce the physiological control of photosynthesis on stomatal resistance to the model. This component of the photosynthetical control in stomatal resistance model not only adds more constrains on the fluxes through the stomata but also produce CO2 flux estimates. Because the current physiological approach requests substantial amount of computer time and is too complex for a GCM or a regional model, some simplification will be made.

In the current physiological approach of stomatal resistance modeling, the gross CO2 assimilation rate is limited by three rates: the efficiency of the photosynthetic enzyme system, the reproduction rate of Ribulose-bisphosphate, and the leaf capacity to export or utilize the products of photosynthesis. we plan to simplify the computation in the co-limitation regime, which will allow us to solve the equations analytically. Therefore, it will substantially simplify the computation.
 

4.3 Convective schemes

The convective activity is a crucial hydrometeorological process in the Amazon Basin. However, the convective processes and its influence on model simulation are uncertain. We will conduct investigation to study the role of moist convection in transferring the energy and to identify the uncertainty in tropical land-atmosphere interactions caused by the cloud scheme. Two cloud schemes: a modified Betts and Miller scheme and a prognostic cloud scheme called McRAS (Microphysics of clouds with Relaxed Arakawa-Schubert Scheme) will be used in the Eta model for comparison. The cloud scheme will also be evaluated using the LBA data. LBA will couple with the TRMM program to provide polarimetric and Doppler radars during the wet season in Rondonia. Besides the precipitation estimated from the radars, the identification of hydrometers, their shape and size, and the circulations within the convective cells will help in the validation of the cloud schemes.
 

4.4 LBA data applications

The parameterizations discussed above will be investigated using observational data from LBA field measurements. During the LBA, measurements will be taken at different scales including about 11 instrumented towers. In the application of LBA field data, we will collaborate with Dr. D. Fitzjarrald of the State University of New York (SUNY) at Albany for the LBA research.
 
 

References

Zhou and Lau, 1989: Does a monsoon climate exist over South America? J. Climate.

Xue, Y., H.G. Bastable, P. A. Dirmeyer, and P.J. Sellers, 1996a: Sensitivity of simulated surface fluxes to changes in land surface parameterization -- a study using ABRACOS data. J. Appl. Meteor., 35, 386-400.

Xue, Y., F.J. Zeng, K. Mitchell, and Z. Janjic, 1996f: The impact of land surface processes on the prediction of the hydrological cycle over the U.S.- A study using a coupled ETA/SSiB model. Preprint of Second International Scientific Conference on the Global Energy and Water Cycle, 73-74.

Images

Figure 1.

Precipitation MapsPrecipitation Maps

Figure 2.
Vegetation Map

 

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