Exploring Trends in Climatological Time Series of Orissa, India Using Nonparametric Trend Tests - Hydrologic Time Series Analysis: Theory and Practice - page 237

Table 11.4. Homogeneity tests of trends of monthly maximum temperature and
monthly minimum temperature for the period 1987-2001

Sources of Monthly maximum Monthly minimum

variation temperature (T max ) temperature (T min )

F 2 -cal F 2 -cal

d.f. Significance d.f. Significance

Total variation 765.54 192 - 679.95 192 -

Homogeneity 104.12 191 - 174.43 191 -

Season 12.13 11 NS 11.27 11 NS

Station 21.42 15 NS 77.75 15 NS

Season station 70.57 165 NS 85.41 165 NS

Trend 661.42 1 S ( p 0.05) 505.52 1 S ( p 0.05)

Note: d.f. = Degrees of freedom; NS = Not significant; S = significant.

11.4.4 Trends in Time Series of Relative Humidity

The descriptive statistics of monthly average relative humidity for 16 stations
of the study area recorded at 8.30 hours ( RH fn ) and at 17.30 hours ( RH an ) are
presented in Table 11.5. The water vapour over the coastal-belt is more in
comparison to the inland areas. However, unusually low values of relative
humidity have influenced the shape of distribution as obvious from the negative
skewness ( S k ) in most of the stations. The spatial and temporal variability of
water vapour is due to a combination of factors such as the proximity of the
location to the Bay of Bengal, topographic features, and anthropogenic factor
like land-use changes. Decrease in vapour fluxes has occurred due to reduction
in evapotranspiration at places where forest lands were converted to agricultural
lands (Mishra and Das, 1984; Douglas et al., 2006).
Figure 11.5 displays the cumulative frequency distribution for the results
of MK and SR trend test for 192 season-stations relative humidity time series
(12 seasons for each of the 16 stations). For RH fn , 67 and 65% of 192 season-
stations relative humidity time series exhibit positive trends based on the MK
and SR tests, respectively [Fig. 11.5(a)]. However, for RH an , 50 and 56% of
192 season-stations relative humidity time series exhibit positive trends based
on the MK and SR tests, respectively [Fig. 11.5(b)]. Comparatively higher
cases of positive trends indicate an increasing moisture load in the atmosphere.
Significant positive trends, although less in number, were more concentrated
in the monsoon season months. The Kendall slopes indicated that both RH fn
and RH an exhibited an overall moistening trend at a rate of 0.07% yr -1 (standard
deviation 0.48) and 0.01% yr -1 (standard deviation 0.53), respectively. The
location parameters of the box plot showed that the trends of RH fn , and RH an
were more stable in the monsoon and post-monsoon seasons. The test of
homogeneity of the RH fn trend results (Table 11.6) indicates that the overall
trend (F 2 Trend, 1 ) is significant at F = 0.05 level (critical F 2 0.995, 1 = 3.84). This
positive overall RH fn trend ( Z - = 0.37) indicates an overall moistening trend of