Reconstructing Global Precipitation for the 20th Century

1
Reconstructing Global Precipitation for the 20th
Century

• Presented by
• Thomas M. Smith

2
Requirement, Science, and Benefit

• Requirement/Objective
• Climate
• Little or no oceanic precipitation sampling in
  pre-satellite era (before 1979)
• Need analyses to estimate oceanic climate scale
  variations
• Evaluate land ocean multi-decadal precipitation
  changes beginning 1900
• Science
• How much has oceanic precipitation changed over
  the 20th century?
• How well can climate-model precipitation be
  validated?
• Benefit
• Addresses NOAAs research plans to understand and
  predict changes in the global hydrologic cycle,
  included in water and weather and climate
  research
• Analysis of ocean precipitation can be used to
  validate and improve climate models, needed for
  IPCC and other international national
  assessments
• Improved assessments and improved climate models
  are needed for studies of changing fresh-water
  availability, needed for planning for future
  societal needs

3
Challenges and Path Forward

• Science challenges
• Improving precipitation analyses from satellites
  and reconstructions
• Satellite-based analysis improvements to continue
  at STAR/CICS, with partners including U.
  MD/ESSIC, NCDC, and NASA/GSFC
• Improving climate model representation of
  precipitation variations
• Will work with other national and international
  groups to help validate climate models
• Next steps
• Documentation and making reconstruction available
• Investigating ways to improve the reconstruction
• Transition Path
• Making reconstruction available to users
• Plans to update the reconstruction for climate
  possible studies and monitoring

4
Basics of the Reconstruction Problem

• In Situ Sampling
• Land sampling for 20th century from analyses
  Climate Research Unit of Univ. of East Anglia
  (CRU), Global Precipitation Climatology Center
  (GPCC), Global Historical Climate Network (GHCN)
• Time series of of average annual global area
  sampled by each analysis
• Sparse oceanic sampling over most of 20th
  century need to use satellite in situ data
  together to understand ocean-area changes since
  1900

5
Reconstruction Methods

• Two Reconstructions
• Both require high-quality satellite analyses to
  generate statistics needed for historical
  analyses
• STAR contributes to the development and
  improvement of satellite-based analyses needed
• 1. Monthly, fitting gauge data to spatial
  covariance functions, resolves land and oceanic
  interannual variations
• 2. Annual, Canonical Correlation Analysis (CCA)
  precipitation from sea-surface temperature
  sea-level pressure, resolves oceanic
  multi-decadal variations
• Comparison analyses Global Precipitation
  Climatology Project (GPCP), Global Historical
  Climate Network (CHCN), IPCC Assessment report 4
  ensemble of coupled models (AR4)

Smith, T. M., M. R. P. Sapiano, and P. A. Arkin,
2008 Historical Reconstruction of Monthly
Oceanic Precipitation (1900-2006), J. Geophys.
Res., 113, D17115, doi10.1029/2008JD009851. Smi
th, T. M., P. A. Arkin, and M. R. P. Sapiano,
2009 Reconstruction of near-global annual
precipitation using correlations with sea surface
temperature and sea level pressure. J. Geophys.
Res., 114, D12107, doi10.1029/2008JD011580.
Near global averages of CCA annual land
gauge-sampled (upper) and ocean low-frequency
(lower).
6
Merged Reconstruction

• Merged analyses
• Fitting gauge data to spatial modes and the CCA
  (from the previous slide) are merged
• A global monthly analysis is the results
• Comparisons to AR4 model ensemble
• Joint Empirical Analysis Function analysis of
  low-pass normalized data from each
• Shows were the model ensemble climate change
  signal is consistent with the analysis, and where
  it has systematic biases

Smith, T. M., M. R. P. Sapiano, and P. A. Arkin,
2009 Modes of multi-decadal oceanic
precipitation variations from a reconstruction
and AR4 model output for the 20th century,
Geophys. Res. Lett., 36, L14708,
doi10.1029/2009GL039234. T.M. Smith, P.A.
Arkin, M.R.P. Sapiano, C.-Y. Chang, 2010 Merged
statistical analyses of historical monthly
precipitation anomalies beginning 1900.
Submitted to J. Climate. P.A. Arkin, T. M.
Smith, M.R.P. Sapiano, J. Janowiak, 2010
Challenges in Observing Changes in Global
Precipitation. To be submitted to Environmental
Research Letters.
7
Challenges and Path Forward

• Science challenges
• Improving precipitation analyses from satellites
  and reconstructions
• Satellite-based analysis improvements to continue
  at STAR/CICS, with partners including U.
  MD/ESSIC, NCDC, and NASA/GSFC
• Improving climate model representation of
  precipitation variations
• Will work with other national and international
  groups to help validate climate models
• Next steps
• Documentation and making reconstruction available
• Investigating ways to improve the reconstruction
• Transition Path
• Making reconstruction available to users
• Plans to update the reconstruction for climate
  possible studies and monitoring