Abstract
Abstract. In the 1990s, water level in the closed-basin Lake Van located in the Eastern Anatolia, Turkey, has risen up about 2 m. Analysis of the hydrometeorological data shows that change in the water level is related to the water budget of the lake. In this study, stochastic models are proposed for simulating monthly water level data. Two models considering mono- and multiple-trend time series are developed. The models are derived after removal of trend and periodicity in the dataset. Trend observed in the lake water level time series is fitted by mono- and multiple-trend lines. In the so-called mono-trend model, the time series is treated as a whole under the hypothesis that the lake water level has an increasing trend. In the second model (so-called multiple-trend), the time series is divided into a number of segments to each a linear trend can be fitted separately. Application on the lake water level data shows that four segments, each fitted with a trend line, are meaningful. Both the mono- and multiple-trend models are used for simulation of synthetic lake water level time series under the hypothesis that the observed mono- and multiple-trend structure of the lake water level persist during the simulation period. The multiple-trend model is found better for planning the future infrastructural projects in surrounding areas of the lake as it generates higher maxima for the simulated lake water level.
Highlights
Closed-basin lake ecosystems have been important issues in the world since decades
The most recent dry period started in the early 1960s due mainly to the expansion of irrigation that has drained the tributary rivers, reduced the lake level by 23 m, shrunk the lake surface area by 74 %, decreased its volume by 90 %, and increased its salinity from 10 g L−1 to more than 100 g L−1, causing negative ecological changes as well as social problems with impacts on the population residing around the lake (Micklin, 2007)
It is clearly seen that correlograms of the AR(2) models are in a better agreement with the correlogram of the observed lake water level time series for both the mono- and multiple-trend cases
Summary
Closed-basin lake ecosystems have been important issues in the world since decades. A very dramatic example is the Aral Sea from Central Asia that has repeatedly filled and dried under the effect of both natural and human forces. The most recent dry period started in the early 1960s due mainly to the expansion of irrigation that has drained the tributary rivers, reduced the lake level by 23 m, shrunk the lake surface area by 74 %, decreased its volume by 90 %, and increased its salinity from 10 g L−1 to more than 100 g L−1, causing negative ecological changes as well as social problems with impacts on the population residing around the lake (Micklin, 2007) Another example is Lake Urmia in northwestern Iran, one of the largest hypersaline lakes in the world. According to Vaziri (1997), the reasons for the recent increase can be categorized from the implementation of the former Soviet Union’s projects to the earth’s tectonic movements, from the occurrence of a wet period for the region resulting in increase of river inflows to global warming, and reduction of surface evaporation Another example of water level decline was observed in Lake Toba, Indonesia, due to use of water for power generation (Acreman et al, 1993).
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