Location of Study Catchments Streamgauge Soil Moisture Climate www.sasmas.unimelb.edu.au
Forcing Assumptions No errors in forcing and other observations assumed for “true” run Forcing biases are introduced to simulate uncertainties in observations –Precipitation +33% –Net radiation -20%
Streamflow Assimilation - Single catchment - DischargeSoil Moisture
Streamflow Assimilation - Single catchment - Root ZoneSurface Layer
Surface Soil Moisture Assimilation Eg. Walker et al. (2001) have shown that surface soil moisture assimilation is generally a viable tool for SM updating. Can remote sensing data then be used to further constrain variational type assimilations?
Adjustments to Experiment Runs First initial state estimates are set to average values, rather than extremes Maximum and minimum values are not allowed to be violated Observation errors of forcing data are made more “realistic” by changing pure bias to bias and white noise errors (Turner et al., in review)
Errors and Biases of Forcing Data BiasError Rainfall25% Radiation0%15%
Variational-type Surface Soil Moisture Assimilation Surface SM Runoff Root Zone SM Profile SM
Summary Streamflow Assimilation in subhumid catchments can produce adequate estimates of initial moisture states. DA of surface soil moisture observations can act as an additional constraint for the observed catchment. Assimilation of both observations has potential for use in finding initial lumped moisture states for a LSM for ungauged upstream catchments.
Conclusions States of ungauged upstream basins can be retrieved to a certain extent. Length of assimilation window will have to be variable for different conditions, esp. if extreme climatic conditions exist and/or errors in forcing are large and biased. Some states may not have an impact on the objective function, but may be retrieved using additional observations of other variables. First estimate of initial states can potentially be crucial to success of the proposed DA scheme, hence have to handled appropriately.
Acknowledgment Australian Research Council (ARC-DP grant 0209724) Hydrological Sciences Branch, National Aeronautics and Space Administration (NASA), USA University of Melbourne –Melbourne International Fee Remission Scholarship (MIFRS) –Postgraduate Overseas Research Experience Scholarship (PORES)