Results - Response of Flood Events to Land Use and Climate Change - page 204

temperature. Thus, it could be concluded that the climate change signal has also
been observed in the Barcelonnette area in a statistical point of view. Climate
change does not depend on the local climate variability of the area, and it is better
to consider more meteorological measurement stations to detect climate change in
the wider region.
For graphical illustrations and detection of abrupt points in the precipitation
time series at two stations, Barcelonnette and Allos-Nord, and for maximum
temperatures

at Barcelonnette station, the sequential Mann-Kendall test is

presented in the Sect. 6.12.4 .

6.12.4 Sequential Mann-Kendall Test

To see the changes in the trend over time, sequential values, U(t) and U 0 (t) were
applied, from the progressive analysis of the Mann-Kendall test. U(t) is a stan-
dardized variable and U 0 (t) are computed similarly to U(t) but only backward,
starting from the end of the series. The linear regression model was used to
estimate time trend of selected variables. The results show that all trend lines are
significant at a 5 % level, according to the slope of linear regression for a pre-
cipitation decrease and a maximum temperature increase. In this section, the
results of the sequential Mann-Kendall test for the period from 1961 to 2009 are
presented. Figures 6.73 , 6.74 , and 6.75 show sequential values of U(t) and
U 0 (t) statistics for precipitation (Barcelonnette and Allos-Nord stations) and
maximum temperatures (Barcelonnette station). Horizontal dashed lines are cor-
responding to confidence limits at a 95 % significant level.
Inspecting the plot U(t) of precipitation values from 1961 to 2009
(Barcelonnette), as shown in Fig. 6.73 , two apparent decreasing significant trends
are indicated. The first occurred between 1991 and 1993, and the second Sharp
decline trend started at the end of the 2007 time series, which was significant at
that time. U(t) and U 0 (t) intersect each other at several points and although they do
not clearly intersect each other, some functions begin to diverge, indicating the
starting point of an abrupt change. Based on the results, the sequential Mann-
Kendall test showed evidence of individual abrupt changes in the magnitudes of
precipitation from 1981 to 1982 and from 2001 to 2003.
Inspecting the plot U(t) of the precipitation time series for the period of
1971-2009 (Allos-Nord) as shown in Fig. 6.74 , two apparent decreasing signifi-
cant trends are identified. The first one occurred between 1991 and 1993 and the
second one started in 2009. U(t) and U 0 (t) intersects each other at several points
and although they do not clearly intersect each other, some functions begin to
diverge, indicating the starting point of an abrupt change. Based on the results, the
sequential Mann-Kendall test showed evidence of individual abrupt changes in
magnitudes of precipitation from 1977 to 1981 and in 2009.
Figure 6.75 shows the results of the forward/backward application of the
sequential Mann-Kendall test for the maximum temperature time series at the