Trend Analyses of Meteorological Variables and Lake Levels for Two Shallow Lakes in Central Turkey

Ozlem Yagbasan,Vahdettin Demir,Hasan Yazicigil

doi:10.3390/w12020414

Ozlem Yagbasan, Vahdettin Demir + Show 1 more

Open Access

https://doi.org/10.3390/w12020414

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Abstract

Trend analyses of meteorological variables play an important role in assessing the long-term changes in water levels for sustainable management of shallow lakes that are extremely vulnerable to climatic variations. Lake Mogan and Lake Eymir are shallow lakes offering aesthetic, recreational, and ecological resources. Trend analyses of monthly water levels and meteorological variables affecting lake levels were done by the Mann-Kendall (MK), Modified Mann-Kendall (MMK), Sen Trend (ST), and Linear trend (LT) methods. Trend analyses of monthly lake levels for both lakes revealed an increasing trend with the Mann-Kendall, Linear, and Sen Trend tests. The Modified Mann-Kendall test results were statistically significant with an increasing trend for Eymir lake levels, but they were insignificant for Mogan lake due to the presence of autocorrelation. While trend analyses of meteorological variables by Sen Test were significant at all tested variables and confidence levels, Mann-Kendall, Modified Mann-Kendall, and Linear trend provided significant trends for only humidity and wind speed. The trend analyses of Sen Test gave increasing trends for temperature, wind speed, cloud cover, and precipitation; and decreasing trends for humidity, sunshine duration, and pan evaporation. These results show that increasing precipitation and decreasing pan evaporation resulted in increasing lake levels. The results further demonstrated an inverse relationship between the trends of air temperature and pan evaporation, pointing to an apparent “Evaporation Paradox”, also observed in other locations. However, the increased cloud cover happens to offset the effects of increased temperature and decreased humidity on pan evaporation. Thus, all relevant factors affecting pan evaporation should be considered to explain seemingly paradoxical observations.

Highlights

Lakes are valuable water resources for humans, playing important roles in aquatic and terrestrial ecosystems and the environment [1,2,3,4]
Our study shows that pan evaporation is a complex process for which all variables affecting pan evaporation should be taken into consideration in order to eliminate paradoxical observations, such as decreased pan evaporation with increased temperature as a result of global warming
The results show that three methods (MK, Linear trend (LT), Sen Trend (ST)) had an increasing trend in both lake levels at all confidence levels

Summary

Introduction

Lakes are valuable water resources for humans, playing important roles in aquatic and terrestrial ecosystems and the environment [1,2,3,4]. Owing to the combined impact of anthropogenic activities and climatic variation, many lakes around the world are under threat [5,6]. Global climate change and anthropogenic activities adversely affect both water quantity and quality, having a critical influence on regional sustainable development. A sensitive marker of change, is an important driver for lakes, with an impact on lake ecosystems [7]. Determination and understanding of long-term changes in water levels due to climatic variables are necessary to establish sustainable management of lakes. Shallow lakes Mogan and Eymir, located 20 km south of Ankara in Central Turkey, are important aesthetic, recreational, and ecological resources for the city of Ankara and the town of Gölbaşı (Figure 1)

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