Current Status of Time Series Analysis in Hydrological Sciences - Hydrologic Time Series Analysis: Theory and Practice - page 103

for solute combinations at most sites. The only exception was chloride, which
had the same trend at 60% of the sites. The smoothing technique indicated that
the short-term patterns in precipitation chemistry were not reflected in surface
waters. The magnitude of short-term variations in surface water quality was
generally larger than the overall long-term trend.
Kothyari et al. (1997) analyzed rainfall and temperature (i.e., long-term
monsoon rainfall, number of rainy days during the monsoon season, and
annual maximum temperature) from three stations at Agra, Dehradun and
Delhi for evaluating the changes in regimes in the upper and middle parts of
the Ganga basin in northern India. The nonparametric methods employed to
identify trends showed that the total monsoon rainfall and the number of rainy
days during the monsoon season have a declining trend, whereas the annual
maximum temperature has a rising trend. These changes were found to have
started around the second half of the 1960's. The results of this study suggested
a possible change in the climatic regime of the Ganga basin, which has far-
reaching implications for the Indian economy.
Giakoumakis and Baloutsos (1997) investigated trends in the historic
hydrological time series of aerial annual precipitation and mean annual runoff
from the Evinos River basin in western Greece. Using different tests for
randomness, a statistically significant long-lasting decreasing trend was found
in the precipitation records, whereas a significant fluctuating “local” trend
was detected in the runoff records. Further, it was demonstrated that the
effects of precipitation change on the mean annual runoff can be quantified
through a magnification factor.
Angel and Huff (1997) examined the stationarity and trends of precipitation
records for the period 1901 to 1994 at 304 sites in the midwestern United
States. The results of this study indicated that the stations are more likely to
experience their heaviest rainfall events in more recent years. An analysis of
the geographic distribution of changes in the annual maximum rainfall time
series showed an increase in areas across the Midwest. It was concluded that
the rainfall frequency studies should be updated on a regular basis for maximum
usefulness.
Mirza et al. (1998) highlighted the importance of analyzing the trends and
persistence in precipitation time series. The annual precipitation time series
for the Ganges, Brahmaputra and Meghna river basins were examined for
trends by the Mann-Kendall rank statistic, Student's t -test and the regression
analysis, and for persistence by the first order autocorrelation technique. The
results indicated that the precipitation in the Ganges basin is almost stable,
while in the Brahmaputra basin, decreasing and increasing trends were found
in two subdivisions. One of the three subdivisions in the Meghna basin has a
decreasing trend, while the two subdivisions have an increasing trend. The
Markovian persistence was not found present in the Ganges basin, but it was
present in the two common subdivisions of the Brahmaputra and Meghna
basins.