Current Status of Time Series Analysis in Hydrological Sciences - Hydrologic Time Series Analysis: Theory and Practice - page 104

Tarhule and Woo (1998) analyzed the rainfall records (i.e., annual total
rainfall, number of rainy days, dates of onset, termination and duration of
rainy seasons as well as monthly rainfall, monthly number of rainy days and
various categories of rainfall above certain intensities) at 25 locations in
northern Nigeria to examine the abrupt changes and trends using the Pettitt
and the Mann-Kendall tests. It was found that an abrupt change occurred in
the time series of annual rainfall and number of rainy days, which affected the
areas north of latitude 11° N. However, the sub-periods before and after the
change points was considered to be homogenous. The series of duration of
rainy seasons exhibited no significant trends or jumps. It was concluded that
recent changes in rainfall over the Sahel were driven by a reduction in the
frequency of rainy days of high rainfall intensities during August and September.
The continuation of agricultural activities in the Sahel despite massive
reductions in annual rainfall is attributed to the fact that the high intensity
rainfall does not contribute significantly to crop growth.
Johann et al. (1998) proposed a method for filling gaps in the precipitation
time series obtained from the Emschergenossenschaft and Lippeverband (EG/
LV) in northwest Germany. Several neighbouring stations of the EG/LV
raingauge network were considered. Various time intervals based on
deterministic and statistical approaches were investigated, but the intervals
between 5 and 120 min are discussed in more detail. Based on representative
examples, it was demonstrated how the time intervals influence the quality of
the estimated (gap-filling) rainfall data.
Moraes et al. (1998) investigated change in the patterns of streamflow
and precipitation and its possible relation to man-induced changes in the
Piracicaba River basin of Brazil. With an area of 12,400 km 2 , this basin is a
typical example of new landscape resulting from development in tropical and
sub-tropical regions: establishment of intensive industrial and agricultural
processes were followed by significant population growth and water
management. Statistical analyses were performed using the precipitation,
evapotranspiration and streamflow data from 1947 to 1991. The precipitation
and evapotranspiration data showed significant increasing trends for the entire
basin. Out of eight streamflow gauging stations, four stations showed a
significant decreasing trend. The cause of these trends was attributed to the
export of water from the basin to the metropolitan region of São Paulo city.
De Luís et al. (2000) examined the spatial and temporal rainfall
characteristics in the Valencia region, Western Mediterranean Basin (east Spain)
using the WMO normal period 1961-1990. The dense and homogeneous daily
precipitation database comprising 97 rainfall stations were collected and mean
values, interannual variability and spatial diversification of total and monthly
rainfalls were studied. Trends were analyzed using both parametric and
nonparametric tests. The spatial distribution of rainfall patterns was established
and the homogeneous areas with similar rainfall patterns were detected based
on the Cramér-von Mises test-statistic. The kriging interpolation technique
was used for characterizing the magnitude of detected changes.