NOAA/WDS Paleoclimatology - 19th Century African Instrumental and Documentary Precipitation Data

This article describes a historical archive of proxy and actual precipitation data that extends the African climate record back to the early nineteenth century. The 'proxy' archive includes verbal, documentary references which contain information related to rainfall conditions, such as references to famine, drought, agriculture or the nature of the rainy season. The precipitation archive includes all observations made in Africa during the nineteenth century. It consists of records for 60 stations in Algeria, 87 stations in South Africa and 304 stations scattered over the rest of Africa. Information is particularly plentiful for the 1880s and 1890s. The two parts have been combined into a semi-quantitative regional data set indicating annual rainfall conditions in terms of anomaly classes (e.g., normal, dry, wet). This data set extends from the early nineteenth century to 1900 and distinguishes seven anomaly classes, using numbers ranging from -3 to +3 to represent very wet, wet, good rains, normal, dry, drought, and severe drought. The regionalization is based on 90 geographical regions shown via studies of the modern precipitation record to be climatically homogeneous with respect to the interannual variability of rainfall. The regional aggregation allows the voluminous fragmentary information available in historical sources to be used systematically to produce multiyear time series that can be directly integrated into the modern record for each region. The resultant time series can also be subjected to statistical analysis, in order to investigate nineteenth century climate over Africa. Spatial detail is added to the data set by utilizing a unique methodology based on climatic teleconnections established from studies of rainfall variability over Africa. The historical information and station records have been combined into a file containing a regional anomaly value for up to 90 geographic regions and the years 1801-1900. Gaps necessarily remain in the matrix, but as early as the 1820s over 40 regions are represented. By the 1880s generally around 70 regions or more are represented. African Rain Gauge and documentary information for the 19th Century. African precipitation gauge data: The historical gauge data contains precipitation readings of monthly data for stations in and around Africa. Each station is listed in order, with its location in Latitude (DDDMM), longitude (DDDMM) and altitude (meters). The second line of the header is the mean rainfall for each month, with the total rainfall at the last column. Standard deviations (if available) are listed in the third line of the header. Each subsequent line consists of the actual raw data. The individual record is the 5 letter year code, the 5 letter station code, year, 12 months of data, and the year total. Missing data is noted by 9999 for the months and 99999 for the year. In some cases only the year total was available, denoted by the code letter 'G' after the year (col 15). Each station's data list is terminated by a record list of all 9's. All values are in millimeters per month for the 12 months (Jan to Dec) and the year total in mm/year. African historical regional data: The entry for each region and year includes five points of information. Left to right, these are the region number, year, index class (-3 to +3), the number of entries used to produce the index, and the source of the information. The right hand column on source uses H to designate documentary information, G to designate a gauge record, "regional substitution" to indicate a value obtained from a nearby and high- correlated region, and "spatial reconstruction" to indicate that a technique based on PCs was used to fill in spatial gaps. The precipitation index associated with all gauge and documentary entries is also given in this column. African historical documentary information: The data set is based on geographic regions, the approximate coordinates of which are given below. The geographical distribution of the regions is given in several publications, including Nicholson 1986 and Nicholson 2001. Data are presented as local precipitation index, a wetness index ranging from -3 to +3. For each entry there are five categories of information, indicated respectively by %A, %F, %K, %D, and %T. %A indicates which of the ninety regions the entry applies to. %F indicates the index value(-3 for extremely dry to +3 for extremely wet). %K indicates the geographical area in Africa, usually by country. %D indicates the year or years to which the entry applies. %T gives the information are climate and weather in the year and, in most cases, a source is given.