The behavior of the precipitation in the Great Antilles demonstrate a close relation between the trends observed in the regional atmospheric circulation, specially the strong influence of the Atlantic Anticyclone on the north of the Caribbean area, jointly with the occurrence of another regional phenomena as ENSO and NAO.
Fig. 1: Precipitation anomalies (period 1931–2000).
The precipitation in the eastern region of Cuba have a significant negative trend since the 1970s of the 20th Century; and in some cases since a previous date; while also, negative trends it is observed in Jamaica and in the north of La Hispaniola and Puerto Rico; this behavior is linked mainly with the dominant influence of the Atlantic Anticyclone over these areas. In the central and western part of Cuba and in the south of La Hispaniola and Puerto Rico, where the Atlantic Anticyclone influence is combined with other important meteorological phenomena, is observed a different trend in the annual precipitation.
The Fig. 1 show the geographical distribution of the annual rain anomalies from 1931 to 2000; in this figure can be appreciated, in the most eastern part of the Caribbean, the negative trend of the precipitation, excepting the Cuban western territory where the continental influence is bigger one. A group of long series of precipitation from Cuba was analyzed to get a more comprehensive approach to the precipitation variability since the beginning of the 20th Century. This analysis it is based on the study of the trend of the annual precipitation and rainy days and the study of the anomalies of the annual precipitation regarding the median; the trend of the data series was evaluated for 5% of significance with a group of strong statistical tests (Wald Walfowitz, Spearman coefficient, Mann-Kendal and Pettit). The
selection of the pluviometers to make this study was realized considering that its data series were representative of the regional behavior of the precipitation in the locality where is installed the pluviometer. The criteria to select the regional representative pluviometers was based in the comparison of the annual and seasonal amount of precipitation, the trends observed in the precipitation through the time, the number of rainydays and the meteorological cause of the precipitation in a homogeneous geographical territory. The results of the statistical analysis, based in a rigorous analytical procedure, are presented in the figures and tables. In the areas, where the negative trends are visually and statistically significant can be described the following:
• Reduction of the raining days (Fig. 2). This graph, from a Cuban locality, shows a persistent decrement of the rainy days since the 1930s; which is more remarkable in the rainy days bigger than 50 mm in 24 hours. This behavior is more dramatic in the north eastern Caribbean Region, due to the strongest dominant action of the North Atlantic Anticyclone; in the central and western part of Cuba, the south of La Hispaniola and Jamaica, the rainy days are more variable due to the influence of different meteorological phenomena.
Fig. 2: Annual rainy days in Cuba eastern region.
• A decrease of the amount of the annual precipitation and reduction of the annual precipitation variability in the eastern Caribbean Region, (Fig. 3 to 5, Tab. 3 and 4). The Fig. 3 and 5 show a persistent reduction of the annual precipitation amount in the north eastern Cuba and Dominican Republic; the same behavior is observed in the Fig. 1 in different Caribbean areas where prevail a trend to the reduction of the rain amount since the 1970s. The annual rain anomalies, observed in the Fig. 4 and 5, calculated with the procedure explained in the section of Data and Methodology, confirms the precipitation reduction. In these graphs, it is possible to observe visually the reduction of the variability of the precipitation. Tab. 3 and 4 contain the results of the application of the mentioned statistical methods to the series represented in these graphs; the results demonstrate that the trend to the reduction of the precipitation is statistically significant.
• A remarkable increment of the rain in the dry season and a light reduction of the rain in the rainy season (Fig. 6).
• An increment of the intensity and frequency of drought processes (Fig. 7).
The maximum rains are another important factor for the annual rain behavior in the Caribbean Region. In Cuba, the maximum rains, in 24 hours, shows interesting fluctuations in the last years; Planos and Limia (2005) found changes in the behavior of the maximum rains through the probabilistic analysis (Tab. 5).
These authors divided the series of maximum precipitation in 24 hours in smaller series to apply the Gumbel probabilistic analysis. The precipitation calculated to 100 years of return period has decreased in the last years in the northeast of Cuba; in the western region has increased lightly and, in the central region, presents a significant increment, as consequence of an exceptional phenomenon that produced an amount 867 mm, in 24 hours.
Fig. 3: Annual rain in the North of Cuba eastern region.
Fig. 4: Annual rain anomalies. North of Cuba eastern region.
Fig. 5: Annual rain (left) and anomaly (right) in Dominican Republic, north region.
Tab. 3: Results of the statistic analytical procedure to Annual rain. North of the Cuba eastern region.
Significance level 0.05%.
Test Result Evaluation
Wald-Wolfowitz 4.322.786 Alfa1 = 0.0000 < Alfa 0 = 0.0500 Spearman -5.947.053 Alfa1 = 0.0000 < Alfa 0 = 0.0500 Mann-Kendall -6.200.562 Alfa1 = 0.0000 < Alfa 0 = 0.0500 Pettit 1136.0 Alfa1 = 0.0000 < Alfa 0 = 0.0500
Tab. 4: Results of the statistic analytical procedure to Annual rain. Dominican Republic, North region.
Tab. 5: 24 hours maxima rain in Cuba. Return period 100 yrs, estimated with Gumbel.
Locality Record
Central Cuba region (Cienfuegos) 701 274 634 509
Eastern Cuba region (Holguín) 233 671 334 341
This result is not conclusive for several reasons; first because the absolute maximum values are very influenced by the form like the statistical sample is made to build the series and, particularly, for the way like are considered the outliers in the probabilistic analysis. The Tab. 5 show that the sub-series 1930-1949 and 1970-1989 have a similar behavior, but it is not a reason to speak a priori of significant changes in the last years. However, like part of the general conditions that is observing in the behavior of the climate, is necessary to study the decrease of the maximum precipitation amount in the last years, to identify if it could be consequence of changes in the meteorological system responsible of the intensive and high precipitation. The frequency of the precipitations that produce amount bigger than 50 mm reveals also a marked negative trend in the areas where the trend of the annual rain is negative (Fig. 8).
-150
1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996
Years
Anomalies(mm) 1941 1946 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996
Years
Fig. 6: Precipitation anomalies less raining months (left), and raining months (right). Period 1941–
1996 respect to period 1961–1990.
In the Caribbean Region, the rain is the only source of production of water, and of course, the runoff has a similar behavior of the rain, although more or less accentuated by the specific characteristics of each place. The Fig. 9 and 10 shows as the runoff in Cuba and Jamaica have similar trends to the described in this paper for the rain and Fig. 11 show the runoff station locality. The above mentioned, means that in Cuba and Jamaica a negative trend in the annual runoff values prevails, with a decrement of the runoff variability in the 1990s decade.
0 0,2 0,4 0,6 0,8 1 1,2
1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995
Years
% affected territory
Fig. 7: Frequency of drought processes in the North of the Caribbean region.
Fig. 8: Annual Frequency of Rains bigger than 50 mm in Cuba eastern area.