Using variograms to detect and attribute hydrological change
There have been many published studies aiming to identify temporal changes in river flow time series, most of which use monotonic trend tests such as the Mann–Kendall test. Although robust to both the distribution of the data and incomplete records, these tests have important limitations and provide...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2015-05-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/19/2395/2015/hess-19-2395-2015.pdf |
| Summary: | There have been many published studies aiming to identify temporal changes
in river flow time series, most of which use monotonic trend tests such as
the Mann–Kendall test. Although robust to both the distribution of the data
and incomplete records, these tests have important limitations and provide
no information as to whether a change in variability mirrors a change in
magnitude. This study develops a new method for detecting periods of change
in a river flow time series, using temporally shifting variograms (TSVs) based
on applying variograms to moving windows in a time series and comparing
these to the long-term average variogram, which characterises the temporal
dependence structure in the river flow time series. Variogram properties in
each moving window can also be related to potential meteorological drivers.
The method is applied to 91 UK catchments which were chosen to have minimal
anthropogenic influences and good quality data between 1980 and 2012
inclusive. Each of the four variogram parameters (range, sill and two
measures of semi-variance) characterise different aspects of the
river flow regime, and have a different relationship with the precipitation
characteristics. Three variogram parameters (the sill and the two measures
of semi-variance) are related to variability (either day-to-day or over the
time series) and have the largest correlations with indicators describing
the magnitude and variability of precipitation. The fourth (the range) is
dependent on the relationship between the river flow on successive days and
is most correlated with the length of wet and dry periods. Two prominent
periods of change were identified: 1995–2001 and 2004–2012. The first
period of change is attributed to an increase in the magnitude of rainfall
whilst the second period is attributed to an increase in variability of the
rainfall. The study demonstrates that variograms have considerable potential
for application in the detection and attribution of temporal variability and
change in hydrological systems. |
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| ISSN: | 1027-5606 1607-7938 |