en |
Long-term periodic structure and seasonal-trend decomposition of water level in Lake Baiyangdian, Northern China
Wang, F.; Wang, X.; Zhao, Y. & Yang, Z. F.
Abstract
Water level, as an intuitive factor of hydrologic
conditions, is of great importance for lake management. In
this study, periodic structures of water level and its fluctuations
in Lake Baiyangdian are analyzed based on
wavelet analysis and seasonal-trend decomposition using
local error sum of squares (STL). Data of monthly time
series are divided into three types with emphasis on
anthropogenic influence from water allocation. It is found
that intra-annual characteristics of water level fluctuations
are the common periodic structures. Water allocation alters
the periodic structures by decreasing and weakening the
oscillations of water level, compared with the slight effects
of natural hydrologic water supplies and short-term climate
changes. An irregular water level decline and short-term
oscillation with irregular periodicity are deduced from
seasonal-trend decomposition analysis using STL. With
seasonality depicted monthly, the influence of water allocation
implies irregular oscillations with high-frequency
components, especially for monthly changes. The water
level fluctuations are influenced by seasonal changes, as
demonstrated by three types of time series. The impacts of
water allocation on seasonality show the differences with
continuous single-peak oscillations representing no influences
and continuous double-peak oscillations representing
frequent influences. Furthermore, the accumulation of
water allocation shows a slight rising trend in average
monthly level fluctuations over the last several years. The
study helps understand periodic structures and long-term
trend changes of water level fluctuations, which will
facilitate lake management of Lake Baiyangdian.
Keywords
Periodic structure; Water level fluctuation; Wavelet analysis; Seasonal-trend decomposition analysis using local error sum of squares; Lake Baiyangdian
|