Rain on small tropical islands

Abstract

[1] A high-resolution rainfall climatology based on observations from the Tropical Rainfall Measuring Mission's Precipitation Radar (PR) instrument is used to evaluate the influence of small tropical islands on climatological rainfall. Islands with areas between one hundred and several thousand km 2 are considered in both the Indo-Pacific Maritime Continent and Caribbean regions. Annual mean climatological (1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) rainfall over each island is compared with that over the surrounding ocean region, and the difference is expressed as a percentage. In addition to total rainfall, rain frequency and intensity are also analyzed. Results are stratified into two 12 h halves of the diurnal cycle as well as eight 3 h periods, and also by a measure of each island's topographic relief. In both regions, there is a clear difference between larger islands (areas of a few hundred km 2 or greater) and smaller ones. Both rain frequency and total rainfall are significantly enhanced over larger islands compared to the surrounding ocean. For smaller islands the enhancement is either negligibly small, statistically insignificant, or, in the case of Caribbean rain frequency, negative. The enhancement in total rainfall over larger islands is partly attributable to greater frequency and partly to greater intensity. A diurnal cycle in island enhancement is evident in frequency but not intensity, except over small Caribbean islands where the converse is true. For the larger islands, higher orography is associated with greater rainfall enhancements. The orographic effect is larger (percentagewise) in the Caribbean than in the Maritime Continent. Orographic precipitation enhancement manifests more strongly as increased frequency of precipitation rather than increased intensity and is present at night as well as during the day. The lack of a clear diurnal cycle in orographic enhancement suggests that much of the orographic rainfall enhancement is attributable to mechanically forced upslope flow rather than elevated surface heating.

A review of observed and projected changes in climate for the islands in the Caribbean

“…There is consistency with the results of Biasutti et al (2012) who use TRMM high-resolution data to show that precipitation over the Caribbean islands is more frequent than over the adjacent ocean during the wet season months due to land-sea thermal contrast. Sobel et al (2011) also demonstrate that there is a significant increase in average island precipitation (relative to the ocean surrounding it) for large islands with mountainous topography. The authors, however, suggest that small islands receive less precipitation than the surrounding ocean (Sobel et al, 2011).…”

“…Sobel et al (2011) also demonstrate that there is a significant increase in average island precipitation (relative to the ocean surrounding it) for large islands with mountainous topography. The authors, however, suggest that small islands receive less precipitation than the surrounding ocean (Sobel et al, 2011).…”

“…(Granger, 1985;Taylor and Alfaro, 2006). Precipitation magnitude varies considerably from the Bahamas to the southernmost islands of the Lesser Antilles and mountainous topography and its orientation with respect to the direction of trade winds further yield large spatial variations in precipitation on many islands (Granger, 1985;Sobel et al, 2011). A prominent feature of the seasonal cycle of precipitation is the mid summer drought (MSD) (Magaña et al, 1999), which is not a real drought but a period during the wet season months when precipitation is relatively lower resulting in a bimodal cycle of precipitation.…”

“…The degree to which the presence of an island can influence regional circulation depends on the island's size and topographic features (Sobel et al, 2011). This effect is small for the small islands in the Caribbean (Chan et al, 2011;Sobel et al, 2011).…”

The influence of sea- and land-breeze circulations on the diurnal variability in precipitation over a tropical island

“…Moreover, tropical pre-cipitation is usually due to convection (Dai, 2001). Tropical convection is also well known to have an important influence on the large-scale atmospheric circulation (Neale and Slingo, 2003;Sobel et al, 2011).…”