37 Figure 3.2: Daily wind speed in two stations over Semarang city, a Semarang
station, b Ahmad Yani station, and c average of both stations 1 January 1994 – 31 December 1999.
3.2 Trends of Historical Climate in Semarang
3.2.1 Rainfall
In general, it was shown in previous study that the observed rainfall in Indonesia experienced decreasing trends after 1970s IPCC 2007. If we investigate the rainfall
over different regions in Indonesia, it is possible that the trend will vary. Here we investigate the trends of rainfall in Semarang city as respectively shown in Figure
3.3.
Based on the average of observed rainfall from five rain gauge stations over Semarang city during 1970-2000 periods, it is found that there is no considerable
trend of rainfall in all seasons Figure 3.3. This is supported by the result of Mann-
38 Kendal statistical test as performed in Table 3.2. However, this result will slightly
different with spatial distribution of rainfall trends in the city as performed in Figure 3.4. The absence of trend in the averaged rainfall is likely caused by uneven spatial
distribution of rainfall trends within Semarang city Figure 3.4. This contributes to the average value of rainfall that seems to show no significant trend in all seasons.
Figure 3.3: Observed seasonal rainfall over Semarang averaged from five rain gauge
Table 3.2: Mann-Kandal Test for Detecting Trend Season
Slope Lower
Upper Z
DJF -0.58574
-4.73124 2.799827 -0.31889 MAM
-1.2 -3.72318 1.572046 -0.74932
JJA -0.20784
-1.71996 1.347403 -0.20847 SON
0.859804 -2.92664 4.105129 0.625407
Figure 3.4: Spatial patterns of seasonal rainfall trends over Semarang. It should be noted that the selection of different ranges of data will affect the trend
and the result of statistical test conducted in this study. Therefore, despite the use of ~30 year observed data, a longer period of rainfall is also needed in order to confirm
100 200
300 400
500 600
1970 1975
1980 1985
1990 1995
2000
Year S
e a
s o
n a
l R
a in
fa ll
A v
e ra
g e
DJF MAM
JJA SON
