Page 208 - Contributed Paper Session (CPS) - Volume 1

CPS1280 Willard Z. et al.
is a monotonic downward trend in the rainfall, whilst a positive z-statistic
shows that there is a monotonic upward trend. There is generally monotonic
downward trend in all the stations for May with significant trend for Paarl
station (p=0.041). However, in June there is generally monotonic increasing
trend with significant trend for Hermanus (p=0.025) and Strand stations
(p=0.005). There were no significant change in the trend for July and August.
The overall seasonal trend (MJJA) for all the stations was not uniform. Cape
Town WO has a significant monotonic downward trend (p=0.040), whilst
Strand station has a significant monotonic upward trend (p=0.037). The results
from MK Test were generally not uniform for the region. In order to find out
if the variability is consistent for the region for the months under study, spatial
analysis was done.

Table 1. Z-statistic values of seasonal rainfall using MK for Stations in Western Cape Province
Station May June July August MJJA
Cape Point -0.100 0.352 1.018 1.634 0.327
Cape Town Slangkop -0.451 0.056 0.394 0.480 0
Cape Town WO -1.938 -0.537 -0.397 -0.350 -1.985*
Hermanus -1.902 2.264* 1.268 0.604 1.479
Malmesbury -0.545 0.967 0.074 0.670 0.174
Molteno Reservoir -1.265 0.099 -0.421 -0.272 -0.868
Paarl -1.881* -0.600 -0.664 -0.049 1.508
Robbeneiland -1.542 0.537 -0.140 0.724 -0.397
S. A. Astronomical Observatory -1.106 -0.377 -0.653 -0.050 -1.257
Stellenbosch -1.220 1.132 -0.754 0.565 -0.352
Strand -0.620 2.454* 1.410 0.338 2.087*
*z-statistic is significant at 0.05 level

CV% was calculated for different stations and kriging was used to find the
spatial patterns of the rainfall. The spatial analysis of the Western Cape map is
presented in figure 2 below. June is the least variable with CV% of between
40% and 59% and May has CV% of up to 68%. The average CV% for all the
months is approximately 50%. May and August are more variable than June
and July which are the wettest months. In May most part of the region selected
has CV% above 57% whilst the CV% for the greater part of the region is less
than 50%.

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