Principal Investigator (PI): Ali Behrangi, NASA's Jet Propulsion Laboratory
The suite of current Global Precipitation Climatology Project (GPCP) precipitation products based on global observational data has become a science community standard, having been cited in over 4000 journal articles. The current monthly (1979–present) and daily (1996–present) products have been developed by research groups over the last 20 years. The GPCP is the precipitation component of an internationally coordinated set of (mainly) satellite-based global products dealing with the Earth’s water and energy cycles, under the auspices of the Global Energy and Water cycle Exchanges (GEWEX) of the World Climate Research Programme (WCRP).
We are using the strengths offered by recent space-borne sensors and retrieval methods to generate the next generation GPCP merged precipitation products in high latitudes (GPCP V3.HL) poleward of 40° latitude and integrate them to the latest GPCP products. Improving the GPCP data products over such climate-sensitive and hydrologically important regions has remained a major need because GPCP uncertainties are the highest in high latitudes (Estimating Climatological Bias Errors for the Global Precipitation Climatology Project (GPCP) Adler et al., 2012) and there has been no focus on GPCP updates in high latitudes over the last 20 years.
The work will improve GPCP in high latitudes based on the emergence of advanced NASA sensors, improved retrieval techniques, international efforts on precipitation measurement in high latitudes, and advances in numerical modeling. The objective of the project is to identify, quantify, diagnose, and reduce uncertainties in the GPCP data products in high latitudes and generate an improved long-term GPCP data record calibrated to the recent observations from NASA’s missions and in-situ observations from international groups. Connecting these new short-term measurements to the long-term GPCP analysis will amplify the impact of NASA’s new missions.
The work will use various emerging capabilities to revise the GPCP data products in high latitudes. These include, but are not limited to:
- Rainfall and snowfall data from NASA CloudSat mission (2006–present),
- Snow accumulations through mass balance analyses based on NASA Gravity Recovery and Climate Experiment (GRACE) mission (2003–present),
- Advances in high latitude precipitation estimation driven by the NASA Global Precipitation Measurement (GPM) mission,
- Recent international projects that enhanced snowfall observations and bias correction for gauges,
- Recent oceanic shipboard precipitation observations (OceanRAIN) for surface validation, and
- New generation of reanalysis (e.g., NASA's Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and high resolution regional models (i.e., RACMO2).
The work will involve a major shift to new data streams, modern Level 2 algorithms, advanced merger techniques, and finer time and space resolutions. We will complement the latest version of GPCP (V3), currently being finalized (under a previous MEaSUREs project, Next-Generation Global Precipitation Climatology Project (GPCP) Data Products, PI: Huffman), that focuses on improvement of GPCP over low and middle latitudes using Tropical Rainfall Measuring Mission (TRMM) and GPM data. We will also build on the methods developed under another MEaSUREs effort (PI: Adler), providing error estimates for precipitation products at monthly to daily time scales, so that the revised GPCP products will have bias and random error estimates with unprecedented accuracy.
The project will produce improved monthly GPCP in high latitudes using recent data sets and use the new calibrations to update the entire GPCP record (1979–present) at 0.5° x 0.5° spatial resolution, consistent with GPCP V3. Accordingly, daily products will be improved through updated Level 2 products and will be adjusted to monthly products using the standard GPCP procedures.
Therefore, the work will complement previous MEaSUREs investment, so that the next generation of GPCP will include updates across the entire globe. We will also provide an additional combined observation-model analysis.