In response to an increasing scientific and humanitarian need to place recent seasonal and multiannual east African precipitation extremes into a historical context, the CHC and Florida State University (FSU) pooled their station archives and expertise to produce a high-quality gridded Centennial Trends precipitation data set.
CenTrends does not imply centennial linear trends in African rainfall, but rather, a data set supporting the analysis of seasonal and decadal excursions within a centennial context. The objective of CenTrends is to provide a reasonably complete and accurate set of gridded seasonal precipitation products for east Africa (-15°S-18°N, 28°E-54° E) from 1900 to 2014.
Extensive quality control of the data was maintained, and seasonal and monthly station data anomalies were interpolated using kriging. The CenTrends data set has more than twice as many observations as the monthly Global Historical Climate Network (GHCN). However, station density is still low (one station per 10,483 km2). The CenTrends acquisition process is a work in progress: gaps remain in Ethiopia prior to 1961; in Uganda, Rwanda, Burundi, Eritrea, and Somalia after 1999; in Rwanda, Burundi, Tanzania and Somalia prior to 1921; and in Eritrea prior to 1941. Efforts to improve the FSU/CHC archive continue.
- There are important differences in the overall coverage between countries. For example, Tanzania and Kenya have relatively dense observation networks stretching back to 1900, especially in the Serengeti region. Ethiopia, on the other hand, has very few available stations before 1961. After 1961, an active meteorological agency and accessible data sharing policy provides good coverage through 2014. Coverage in Eritrea and Somalia is generally limited.
- The CenTrends analysis uses the Climate Hazards Center’s Precipitation climatology (CHPclim) as a background climatological mean state.
The code used to produce the CenTrends data set was written by Chris Funk and is freely available at ftp://ftp.chg.ucsb.edu/pub/org/chg/products/CentennialTrends/R_code/.
Data Records (unlimited length)
- Version 1 of the CenTrends data set provides four sets of seasonal east African precipitation totals: March-June, June-September, October-February, and October-September. An additional set of monthly data was also produced.
- The domain selected extends from 28°E to 54°E, 15°S to 18°N. Each field has 261 columns and 331 rows. The upper-left corner of these data center on 18°N, 28°E.
- Each season's CenTrends data are provided in a single netcdf format file, following standard CF4 (climate and forecast) metadata conventions. Another netcdf file contains the 12 months x 115 years of monthly gridded CenTrends fields. This data (Data Citation 1) is hosted on the CHG FTP site in ftp://ftp.chg.ucsb.edu/pub/org/chg/products/CentennialTrends and can also be accessed at http://datadryad.org.
- Each individual netcdf file contains five netcdf variables: seasonal or monthly precipitation totals (mm), seasonal or monthly precipitation kriging standard errors (mm), time in days since 1900, and latitude and longitude.