Alpine Precipitation Analyses
from High-Resolution Rain-Gauge Observations

Shepard D.S., 1968: A two-dimensional interpolation function for irregularly-spaced data. Proceedings of 1968 ACM National Conference, 517-524.

Shepard D.S., 1984: Computer mapping: The SYMAP interpolation algorythm. In: Spatial Statistics and Models, (Eds. G.L. Gaile and C.J. Willmott), 133-145.

Willmott C.J., Rowe C.M., Philpot W.D., 1985: Small-scale climate maps: a sensitivity analysis of some common assumptions associated with grid-point interpolation and contouring. The American Cartographer, 12, 5-16.

The actual version 4.0 of the Alpine climatology was released in October 1997 and covers the period 1971-1990. A detailed description of the dataset and analysis method for version 4.0 is given in Frei and Schär (1998) and also includes a climatological analysis over this 20 year reference period. In March 1998 analyses for the recent years (1992-1995) were made accessible. While dense for most regions, this update is based on coarser data over Northern Italy (SYNOP coverage only) however.

Versions of the Alpine precipitation climatology:

Version Nr.	Date of Release	Changing Characteristics
V4.0	October 1, 1997	Newly includes data from 68 records for Slovenia (south-eastern Alps, full period); Additional 48 records for the northern Appennino during 1987-1990; Some refinements in the extent and magnitude of the moist anomaly over the Carnic and Julian Alps, minor changes elsewhere.
V3.0	May 1, 1997	Newly includes more than 3000 records from France (full climatological period); Significant refinements of the distribution over France and the Southern Alps.
V2.0	Jan 1, 1997	Newly incorporates high-resolution rain-gauge networks for large parts of northern Italy (mostly for 1971-1986) and for Croatia (full period); Reference period changed to 1971-1990; Improved distributions over the Po valley, the Appenines and the eastern Adriatic coast.
V1.5	Jan 1, 1996	Analyses on regular grid in conventional coordinates of geographical latitude/longitude; Database similar like for V1.0.
V1.0	July 1, 1995	Original public version; Analyses on rotated spherical grid (0.25 degrees resolution); Based on high-resolution networks for Austria, Germany and Switzerland, SYNOP coverage elsewhere; Reference period 1973-1992.

A number of climatological charts from the actual analyses (V4.0) is available directly in picture format. Select the desired field, month and preferred format to get the chart. These sample fields can also be accessed in digital format (Digital Access).

This site offers access to several products from the latest version (see Versions) of the Alpine Precipitation Climatology in the form of ASCII-files:

Available Fields

• Climatology of Monthly Precipitation

  Monthly gridded analyses of mean precipitation (in mm per day) for the 20 years reference 1971-1990.

• Climatology of Strong Precipitation

  Monthly grids with the frequency of days for which the daily total exceeds the threshold 20 mm. Valid for the 20 years reference 1971-1990. Frequencies determined individually for the time series and subsequently analysed on the grid. Frequency given in % of days.

• Daily Precipitation Analyses

  Comprehensive set of mesoscale gridded daily precipitation (in mm) for the period from January 1, 1971 till December 31, 1992.

Conditions for Access

• Digital products of the Alpine precipitation climatology are distributed for scientific research and educational, non-commercial activities. The fields are available from the Data Centre of the Mesoscale Alpine Programme (MAP) and access is free of charge. The Intergovernmental Panel of MAP has approved access to the gridded database at its meeting in June 1997.

• When using the products of the Alpine precipitation climatology in publications (any media, scientific literature, the Internet or others) please make reference to the description of the database in Frei and Schär (1998) and indicate that the data was retrieved from the MAP Data Centre. The version number of the products used should also be specified (see Versions).

• The climatological fields belong to category 'required data' as defined in the MAP Data Access Policy, while the daily analyses fall under category 'supplemental data'. The latter products are available for registered users of the MAP Data Centre only. Access to supplemental data may be obtained upon formally accepting specific conditions placed by the original data providers. Refer to "Access to Supplemental Data" for details of this access procedure.

• Users should carefully take into consideration the error sources discussed in Frei and Schär (1998) and the Interpretation Hints on this site.

• Users of the digital products are invited to notify their retrieval to Ch. Frei (email address: s. at the beginning of this document) including a brief description about the intended use. Such users will automatically receive information on newly available and improved versions of the products.

File Format:

• files:

  pure ASCII-files, compressed using gzip.

• naming and size:

  RRCL.TXT: monthly fields of mean precipitation (about 50 kB)
  RF20.TXT: monthly fields of strong precipitation (about 50 kB)
  RR19xx.TXT: daily fields of precipitation for year 19xx (about 1 MB each)
  

• heading lines:

  head: data source and version number
  title: field type (parameter) and unit
  time: year or reference period of the climatology
  dimensions: dimensions of the analysis grid in longitude (x), latitude (y) and time (t),
  loc of (1,1): lower left corner in degrees lat/lon,
  loc of (nx,ny): upper right corner in degrees lat/lon.
  missing data flag: indication used to demark missing analysis (insufficient observations)
  

• data block:

  The data block follows the heading lines and comprises the two-dimensional analyses grids sequentially in time. Each of the fields is preceded by a line of the form nt=time, where time is either the number of the month (for the climatological fields) or the number of the day (for the daily analyses fields). Each of the 2D-fields is stored row-by-row from the south-western to the north-eastern corner of the analysis domain.

Download ...

Climatological Fields	Daily Analysis Fields
RRCL.TXT.gz RF20.TXT.gz	RR1971.TXT.gz RR1972.TXT.gz RR1973.TXT.gz RR1974.TXT.gz RR1975.TXT.gz RR1976.TXT.gz RR1977.TXT.gz RR1978.TXT.gz RR1979.TXT.gz RR1980.TXT.gz RR1981.TXT.gz RR1982.TXT.gz RR1983.TXT.gz RR1984.TXT.gz RR1985.TXT.gz RR1986.TXT.gz RR1987.TXT.gz RR1988.TXT.gz RR1989.TXT.gz RR1990.TXT.gz RR1991.TXT.gz * RR1992.TXT.gz * RR1993.TXT.gz * RR1994.TXT.gz * RR1995.TXT.gz *

* The analyses on these files should be considered as preliminary over Northen Italy (see Interpretation Hints).

The nature of rain-gauge data and the variable density both in time and space require some care in the interpretation of the results of the Alpine precipitation climatology. Here we list some of the most important items, a detailed discussion can be found in Frei and Schär (1998).

• * The daily analyses for 1991-1995 are preliminary. The underlying data base for Northern Italy is very poor. For this area data was essentially restricted to conventional SYNOP stations with poor density and limited data quality. The analyses will be repeated when high-resolution data will become available for these regions.

• No correction was made of the systematic measurement bias of the rain-gauge measurements. Underestimates may be large in winter-time.

• The spatial analysis does not compensate for the unrepresentative distribution of the observing network with respect to topographic height.

• Random errors due to limited spatial sampling add up to the systematic errors. For annual and monthly climatologies these are estimated in the order of 5-10%.

• The network varies in time. No compensation was made for temporal inhomogenieties.

• The grid-resolution is 25 km, features below this scale are not resolved.

• The resolution of the analyses may occasionally be coarser than the grid-resolution, depending on data density.

• The data density is still poor for Northern Italy after 1986, resulting in a lower reliability of the analysis.

• The network over the Dinaric Alps is somewhat less dense than for other parts of the domain. Here daily analysis often do not attain grid-resolution.

• Frei C., 1995: An Alpine precipitation climatology based on high-resolution rain-gauge observations. MAP Newsletter, No. 3, 46-47.

• Frei C., and Schär, C., 1997: The frequency of heavy Alpine precipitation events: Results from the updated rain gauge dataset. MAP Newsletter, No. 7, 46-47.

• Frei C., and Schär, C., 1998: A precipitation climatology of the Alps from high-resolution rain-gauge observations. Int. J. Climatol., 18, 873-900. [order reprint from Ch. Frei]

• Frei C., and Schär C., 2001: Detection probability of trends in rare events: Theory and application to heavy precipitation in the Alpine region. J. Climate (in press). [order preprint from Ch. Frei]

• Schär C., Davies T., Frei C., Wanner H., Widmann M., Wild M. and Davies H.C., 1998: Current Alpine Climate. In: Cebon P., Dahinden U., Davies H.C., Imboden D., Jäger C. (Eds): A View from the Alps: Regional perspectives on climate change. The MIT press, 21-72.

• Widmann M., and Schär C., 1997: A principal component and long-term trend analysis of daily precipitation in Switzerland. Int. J. Climatol., 17, 1-24. [order reprint from Ch. Frei]

• Schwarb M., 2000: The Alpine precipitation climate - Evaluation of a high-resolution analysis scheme using comprehensive rain-gauge data. Diss ETH No. 13911.

• Schmidli J., 2000: Reconstruction and analysis of mesoscale precipitation in the Alps for the 20th century. Diss ETH No. 13967.

• Schmidli J., Frei C., and Schär C., 2001: Reconstruction of mesoscale precipitation fields from sparse observations in complex terrain. J. Climate (in press). [order preprint]

Acknowledgements

We are indebted to the following institutes for providing access to daily precipitation data: Deutscher Wetterdienst, Offenbach a.M.; Hydrographisches Zentralbüro des Bundesamtes für Land- und Forstwirtschaft, Wien; Zentralanstalt für Meteorologie und Geophysik, Wien; Météo France, Toulouse; MeteoSwiss, Zuerich; Servizio Idrografico e Mareografico Nazionale, Roma; Ufficio Centrale di Ecologia Agraria, Roma; the Italian MAP working group on climatology; Croatian Meteorological and Hydrological Service, Zagreb; Hydrometeorological Institute of Slovenia, Ljubljana.

Send Questions and Comments to Ch. Frei