Rainfall variability in Congo-Brazzaville: 1932-2007

摘要

The interannual variability of rainfall amounts and rainy days is analysed from synoptic stations located in different climatic zones of Congo-Brazzaville over the common period 1932-2007. The annual and seasonal rainfall evolution is appreciated using standardized indices. Trends examined were based on the non-parametric Mann-Kendall test (the major synoptic stations point out alternative periods of anomalies-positive and negative). A majority of negative anomalies is recorded during the 1930s and 1940s. The decade 1950 shows mainly positive anomalies with the exception of 1958 which records a general precipitation deficit all across Congo. The decade 1960 is characterized by precipitation excess over the whole Congo. The decades 1980 and 1990 experience the largest rainfall deficit (about 10-20% below the long-term mean). The evolution of the precipitation at Brazzaville is particularly stable, although there are large positive anomalies during the 1990s. The transition between positive and negative anomalies decades is not uniform across Congo. The progressive non-parametric Mann-Kendall trend test shows that there is stability in the annual rainfall and rainy days over the southern area in the period 1932-2007. By contrast, the annual rainfall for the northern stations shows a significant decline since about the 1980s. In the south the decline is observable only in the evolution of the March-May seasonal rainfall. In most of the stations there is a precipitation increase during the September-November rainy season.