WCRP Workshop on Determination of Solid Precipitation in Cold Climate Regions

1. WCRP Workshop on Determination of Solid Precipitation in Cold Climate Regions Fairbanks, Alaska June 9-14, 2002

2. Organized by: WCRP CliC and GEWEX Projects Host: University of Alaska Fairbanks (UAF) Sponsors: WCRP and GCOS Meteorological Service of Canada NOAA Arctic Research Office NOAA/NASA GEWEX Americas Prediction Project UAF International Arctic Research Centre UAF Water and Environmental Research Centre

3. Participation: • Over 50 invited participants from 13 countries. • Representation from the major cold regions of the world including North and South America, Scandinavia, Eurasia, China and the Arctic and Antarctic. • Experts on cold climate precipitation; in-situ measurement and remote sensing; development of precipitation adjustment techniques and implementation on regional and global scales; major field programs; global data archives and modeling. • Over 50 paper and poster presentations.

4. Workshop Objectives: • to review the current status of measuring or determining precipitation, especially solid precipitation, in cold climate regions • to identify gaps and issues • to recommend actions that will allow us to determine precipitation over a range of time and space scales for climatological and hydrological analyses, regional water budgets, validation and process experiments and models

5. WG1: Precipitation Measurement • Conventional measurement methods • Alternative strategies • New technologies

6. WG1: Precipitation Measurement Issues: • impact of automation on precipitation measurement and related QA/QC challenges; • continuing need for conventional point precipitation measurements against declining networks in many countries; • accessibility of up-to-date meta data; • need to blend (fuse or combine) data from different sources (in-situ, model, satellite); • need to maintain reasonable expectations on what satellite and radar technologies are able to provide; and • need for further intensive field efforts to address scaling.

7. WG1: Precipitation Measurement Suggested actions: • establish a WCRP working group to develop guidelines on the minimum station density required for climate research studies on solid precipitation in cold climate regions; • conduct urgently needed research to determine how to obtain climate quality data from automated weather observing systems--need to define and attribute “climate”-quality to operational weather observing systems/sites; • encourage national research agencies to establish programs to provide support for the development of new instruments to measure solid precipitation in high latitude region; and • identify and establish intercomparison sites for standardized testing of new technology, such as radar, hot plate, pressure, or blowing snow

8. WG2: Measurement Errors and Adjustment Procedures Issues: • is there a need for intercomparison of adjustment procedures; • how can we quantify and/or represent the error in the adjusted measurements and monitor the improvements made by making these adjustments; • what are the errors in gridding and creating gridded products; what must be done to the existing and planned national networks and archives to provide consistent adjustments to facilitate comparisons among national, regional and global climatologies; and • what is the practicality of adjustments related to time scale, space scale and metadata requirements.

9. WG2: Measurement Errors and Adjustment Procedures Findings: • there is real value in reporting adjusted precipitation and there is a continuing need for ongoing intercomparisons; • correction factors are compromised by limited data sets and there are regional/climatic differences in adjustment factors; • the application of real time / dynamic adjustments should be done with caution—we must first determine the limitations; • we need to adapt to changing user needs; and • good meta data and station histories are not only important, but essential.

10. WG3: Global Precipitation Data Sets Questions: • what are the principal user requirements for a global precipitation data set; • what are the limitations in the current global precipitation data sets; • what improvements could/should be made in these global precipitation data sets; • what new measurement techniques (e.g. GPM) could provide data for these global data sets; • what research and development is needed to prepare for these new measurement and data systems; • what are the limitations in merging satellite and in-situ products and how are these limitations overcome; and • is there a role for a data-model mix in producing global precipitation data products?

11. WG3: Global Precipitation Data Sets Research needs: • Improve the use of wind information to enhance adjustments of snow both at a point and over a region; • optimizing the blend of moisture flux convergence and gauge measurements in data sparse areas (e.g. Greenland); • determining how to incorporate non-standard data (e.g. ice cores) into precipitation climatologies; • development of models for downscaling to topography, blending strategies for data assimilation (e.g. define error characteristics), and interpolation to determine large scale precipitation patterns in the absence of data; • estimation of snowfall and snow pack in mountainous regions; and • techniques to distinguish between solid and liquid precipitation.

12. WG3: Global Precipitation Data Sets Recommendations: • provide enthusiastic support to GPM by developing regional baseline data streams for algorithm development; • develop a strategy for exploiting new technologies in the development of algorithms and models for third and fourth generation precipitation climatologies; • use daily precipitation as a building block for precipitation climatologies; • develop a system for a critical mass of snow accumulation stations in Antarctica to provide accumulations with a one-month data latency; • obtain comprehensive meta data on gauge placement; • ensure full data rescue and digitization of “at risk” cold season data sets; and • ensure CliC and GEWEX address the priority research needs (listed above) for developing global precipitation data sets.

13. Gaps and common issues: • precipitation measurement in mountainous regions; • measurement of low intensity solid precipitation events; • measurement /estimation of precipitation in Antarctica; • solid precipitation over sea ice and ice covered Arctic Ocean; • how to quantify the errors associated with adjustment procedures and determine the limitations on time and space scales for adjustments; • gridding—what analysis method to be used and sampling error depend on amount of data; • GPCC—some countries have not provided data since gridded products distributed free; • GPCC—sampling errors have to be addressed by CliC, also how to proceed and methods that can be implemented; and • how to improve the linkage to the GCM community and determining modeling needs.