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Beighley and Moglen (2002) analyzed the trends of nonstationary discharge
corresponding to the periods of urbanization by employing three statistical
tests: one parametric t -test and two nonparametric tests (Kendall's Tau and
Spearman Rank Correlation tests) using the annual maximum discharge and
annual maximum discharge-precipitation ratios series. It was concluded that
the ratios are more effective than the discharges alone for identifying
nonstationarity resulting from urbanization. In addition, the relationships
between measures of urbanization and the presence/absence of significant
trends in the discharge series are presented.
Kahya and Kalayci (2004) presented a trend analysis of 31-year monthly
streamflows obtained from 26 basins of Turkey. Four non-parametric trend
tests (i.e., the Sen's T, Spearman's Rho, Mann-Kendall, and the Seasonal
Kendall), which are popular for detecting linear trends in a hydrological time
series were used. The Van Belle and Hughes' basin-wide trend test was also
included in the analysis. Homogeneity of trends in monthly streamflows was
tested following the method developed by Van Belle and Hughes. Thus, this
study presents a complete application of both the Van Belle and Hughes' tests
for homogeneity of trends and basin-wide trend tests (originally developed for
trend detection in water quality data) in a hydroclimatic variable. The results
revealed that the basins located in western Turkey, in general, exhibit downward
trend (significant at the 0.05 or lower level), whereas the basins of eastern
Turkey have no trends. In most cases, the first four trend tests were found to
yield the same conclusion about the trend existence. Furthermore, based on
the Van Belle and Hughes' basin-wide trend test, some basins located in
southern Turkey were found to exhibit a global trend, which suggests the
homogeneity of trends both in seasons and in stations.
Ludwig et al. (2004) presented a detailed portrait of the average
hydroclimatic patterns in the Têt River basin using the data from 1980 to
2000, which is a typical Mediterranean river in the south of France where
short but violent flash-floods frequently occur. Average temperatures during
the selected period were the warmest of the last century. Average spring
temperatures in the basin followed a highly significant trend of increasing
temperatures. The average autumn temperature, however, decreased and partly
counterbalanced the temperature increase in springs. The mean annual runoff
was found highly variable, but no clear trend over the investigated period was
detected. However, an increasing trend was detected in the flood discharge in
the downstream portion of the basin. Also, the mean annual precipitation over
the entire basin showed no clear evolution, but the contribution from the
upper part of the basin was found decreased, whereas the contribution from
the middle and lower parts of the basin was found increased. It was concluded
that the humidity of Mediterranean origin is more important for the hydro-
climatic functioning of the Têt basin. If the detected trends persist in the
future, the flood frequency is most likely to increase.
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