Trend and Homogeneity in Subsurface Hydrologic Variables: Case Study in a Hard-Rock Aquifer of Western India - Hydrologic Time Series Analysis: Theory and Practice - page 168

outside the 1.5 times box length range from the upper and lower values of the
box. An extreme value is that which is outside the three times box length
range from the upper and lower values of the box (Tukey, 1977).
Moreover, long-term temporal variation of the annual rainfall for the 43-
year period is shown in Fig. 8.3. Clearly, no overall trend in the annual rainfall
is visible, but the presence of outliers indicates that the annual rainfalls in
some of the years at Dhariawad and Kotra stations are substantially higher
than the rainfalls at other stations. Of the total 43-year period, the annual
rainfalls at all the rainfall stations exceeded the mean annual rainfall in five
years (1973, 1983, 1990, 1994 and 2006), whereas they were below the mean
annual rainfall in eleven years (1966, 1972, 1974, 1982, 1986, 1987, 1988,
1995, 1999, 2000 and 2002). Thus, the rainfall in the study area exhibits
considerable variations with space and time.
Fig. 8.3. Spatio-temporal variations of 43 years annual rainfalls.
8.4.2 Trend and Homogeneity in the Annual Rainfall Time Series
Results of the Mann-Kendall, SROC, and Kendall Rank Correlation tests are
summarized in Table 8.1. It can be seen from this table that the calculated test-
statistic values of all three trend tests is more than their critical values at 5%
level of significance (D = 0.05) for Mavli rainfall station, which indicates
presence of trend in the annual rainfall time series of Mavli station. However,
the calculated test-statistic values of all trend tests for the remaining nine
rainfall stations are less than their critical values, and hence there is no trend
in the rainfall series of these stations. Negative test-statistic value of the
Mann-Kendall test suggests declining trend in the annual rainfall time series
of Mavli rainfall station.
Furthermore, the results of the Levene's ANOVA test (Table 8.2) revealed
that the calculated test-statistic value (0.014) is less than its critical value
(1.96) for 9 degrees of freedom in the numerator and 420 degrees of freedom
in the denominator. Hence, the annual rainfalls at the ten rainfall stations do