Monitoring Agricultural Drought in the West Indies - Monitoring and Predicting Agricultural Drought: A Global Study - page 150

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46

arid and southern coastal lowlands, where irrigation is a necessity, and
where average annual rainfall is just > 800 mm (table 11.1). The rest
of the industry, however, is rain-fed and typically receives between 1300
and 1600 mm of rainfall per annum. Even in the irrigated areas there is a
dependence on seasonal rainfall, which is estimated to be responsible for
up to 50% of yields in good rainfall years and 30% in poor rainfall years
(SIRI, 1973).
A boost in early growth of sugarcane usually occurs with the April-
June (early season) rains. The July-September period is regarded as the
“boom period of growth,” because during this period the cane grows at
its fastest rate (Shaw, 1963). Lack of rains during this period has a telling
effect on sugarcane growth. In contrast, good rainfall during this period
can dramatically compensate for severe growth retardation from drought
in the earlier part of the year, as happened in 1998 at the Worthy Park
estate, when the cane yield of 96.81 tons per hectare (tc/ha) was one of the
highest ever recorded. The Frome cane-growing area, which lies in the wet
west and receives nearly 2000 mm of rainfall per annum, shows a tendency
toward bumper crops in years following below normal April-June rainfall
(Felix, 1977).
The industry attempts to harvest as much of the crop as possible between
December and April, taking advantage of the cool and dry period (figure
11.2), which favors sugarcane ripening (Biswas, 1988). The onset of rains
in April-May usually triggers a sharp deterioration in sugar content. Often,
when the dry period is too prolonged due to drought in the early rainfall
season, cane yield begins to be adversely affected.
Four climate-related stresses lead to a poor harvest of sugarcane in Ja-
maica: (1) below-normal July-September rainfall, (2) below normal
November-May rainfall, resulting in poor establishment of plantings and
retardation of early growth, (3) above-normal temperatures and excessive
rainfall during November-March (i.e., four to six weeks before harvest,
and (4) excessive spring rains in poorly drained, flood-prone areas. These
anomalies in seasonal rainfall and temperature are attributed to El Niño or
La Niña events (Spence and Taylor, 2002; Stephenson and Chen, 2002).
To illustrate this we briefly consider the production records from two sugar
estates in Jamaica: Worthy Park, which is situated in the rain-fed area of St.
Catherine in the Central Uplands of Jamaica (table 11.1 and figure 11.3).
An examination of the last 50 years of yield data for sugarcane at
Worthy Park revealed that El Niño and La Niña years reduced yields
in subsequent years. This happened in 10 different years, and the yield
reduction was about 8% from the normal yield of 86 tons/ha (table 11.2).
For example, the June-October rainfall in 1991 was only 46% of normal
rainfall, and the December 1991 to February 1992 rainfall was only 61%
of normal rainfall, and this significantly reduced yields in 1992. In addition,
the minimum temperature was 2.8% above normal. All these weather
anomalies were due to the 1991-92 El Niño. The 1965 El Niño caused

[150

Line
——
0.0
——
Shor
* PgEn

[150