Project Funding: 2014 - 2017

NRA: 2013 NASA: Carbon Cycle Science   

Funded by NASA

Abstract:
The objectives of the proposed work are: 1) to estimate gross primary production (GPP), respiration, net carbon fluxes, biomass, and their uncertainties over the Amazonian forests over a period of 10 years (2003-2012) by assimilating canopy structure and water content, and soil moisture from a combination of QSCAT/OSCAT2 and TRMM-PR satellite data into a coupled data assimilation model, 2) to study the impact of severe climate variability such as 2005 and 2010 droughts on the carbon dynamics and the time-scale of the response of the Amazon forest, 3) to identify poorly represented biogeochemical processes and their timings in the Community Earth System Model (CESM), and 4) to quantify the feedback of drought induced disturbances to precipitation. We will validate the results of the proposed study on carbon cycle and dynamics against independent data products, including observations from FLUXNET (http://fluxnet.ornl.gov/), MODIS GPP/NPP, and biomass spatial products (e.g., Saatchi et al. 2011). We will also verify the CO2 responses to the estimated net carbon flux against GOSAT XCO2, and examine the consistency between bottom-up flux estimation from data constrained CESM and the top-down atmospheric inversion constrained by GOSAT XCO2 observations. The primary methodologies are ensemble Kalman filter (EnKF) coupled with Community Earth System Model (CESM) and atmospheric inversions. The EnKF-CESM includes two components: the atmospheric data assimilation (EnKF-CAM) and the land data assimilation (EnKF-CLM-CN). When these two components run in parallel, the uncertainties estimated from EnKF-CAM and EnKF-CLM-CN will propagate to each other through forecast, which makes the uncertainty quantification more realistic. This study will be the first study considering the uncertainty propagation between atmosphere and land during data assimilation process. The proposed research activities will not start from scratch. It builds upon the ensemble data assimilation system and the atmospheric inversion tools that have been developed (Liu et al. 2009; 2011; 2012; 2013). The quantitative relationships between QSCAT/OSCAT2 and canopy properties, and between TRMM PR observations and soil moisture have been established by Saatchi et al. (2013). The sensitivities of carbon dynamics (e.g., changes in net carbon fluxes) to canopy properties (e.g., Leaf Area Index) and soil moisture have been proved by previous literatures (e.g., Brando et al. 2008) and sensitivity experiments (section 1.2.1). At the end of the proposed research, we expect to deliver the following results: 1) the net carbon fluxes, the gross primary production (GPP), respiration, biomass, and their uncertainties over Amazonia between 2003 and 2012 at grid cells approximately 0.25° in resolution, 2) quantification of the feedback mechanisms of drought induced forest disturbance to precipitation, 3) a comprehensive validation of the net carbon fluxes, GPP, and biomass against independent observation and data products, including the net carbon flux and its uncertainties from atmospheric inversion constrained by GOSAT XCO2 between July 2009 and Dec 2012, and 4) identification of the poorly represented biogeochemical processes and their timings in CESM. The proposed research addresses the following scientific and technical questions: - How did the net CO2 fluxes change in Amazonian forest during the 2005 and 2010 droughts and the subsequent recovery? - What is the feedback magnitude of Amazonian canopy disturbance from droughts to rainfall? - Are top-down flux estimates using satellite column XCO2 consistent with bottom-up flux estimates constrained with canopy structure /water content and soil moisture observations? - What are the main sources of uncertainty in the NCAR/DOE Community Earth System Model (CESM) when simulating the Amazonia droughts and their impacts on the carbon dynamics?

Publications:

Liu, J., Bowman, K. W., Lee, M. 2016. Comparison between the Local Ensemble Transform Kalman Filter (LETKF) and 4D-Var in atmospheric CO 2 flux inversion with the Goddard Earth Observing System-Chem model and the observation impact diagnostics from the LETKF. Journal of Geophysical Research: Atmospheres. 121(21), 13,066-13,087. DOI: 10.1002/2016JD025100

Shi, M., Liu, J., Zhao, M., Yu, Y., Saatchi, S. 2017. Mechanistic Processes Controlling Persistent Changes of Forest Canopy Structure After 2005 Amazon Drought. Journal of Geophysical Research: Biogeosciences. 122(12), 3378-3390. DOI: 10.1002/2017JG003966

2015 NASA Carbon Cycle & Ecosystems Joint Science Workshop Poster(s)

• Estimating the Impacts of Recent Severe Amazonia Droughts on Forest Carbon Dynamics and Fluxes from Assimilating Satellite Observations in NCAR CESM with Ensemble Kalman Filter   --   (Junjie Liu, Sassan Saatchi, Yifan Yu, Kevin W Bowman, Meemong Lee)   [abstract]

More details may be found in the following project profile(s):

• NASA Terrestrial Ecology (TE) Project Profile