scholarly journals Effect of Cascading Reservoirs on the Flow Variation and Thermal Regime in the Lower Reaches of the Jinsha River

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 1008 ◽  
Author(s):  
Lianghong Long ◽  
Daobin Ji ◽  
Defu Liu ◽  
Zhengjian Yang ◽  
Andreas Lorke
Keyword(s):  
Water Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Mitigation Strategies ◽  
Temperature Cycle ◽  
Seasonal Temperature ◽  
Jinsha River ◽  
Seasonal Flow ◽  
Reservoir Construction ◽  
Cascading Reservoirs

We analyzed the alteration of discharge and water temperature caused by two newly established reservoirs in the lower reaches of the Jinsha River. In comparison to longer-term observations from the pre-impoundment period, the seasonal flow variability was significantly affected by the larger, upstream-located Xiluodu reservoir, with higher discharge in spring and reduced discharge in summer. The smaller, downstream located Xiangjiaba reservoir did not contribute significantly to the total hydrological alteration caused by the reservoir cascade. Thermal stratification occurred in spring and summer in the Xiluodu reservoir, but was not observed in the Xiangjiaba reservoir. The vertical structure and seasonal dynamics of thermal stratification were mainly governed by the water temperature of the inflow and the depth of the water outlet. Despite the different thermal structure, both reservoirs reduced the amplitude of annual temperature variations and delayed the seasonal temperature cycle in the downstream river water. In contrast to discharge variation, thermal effects were cumulative along the cascading reservoirs. Homogenization and delay effects can be expected to increase further with the completion of ongoing reservoir construction upstream of the two studied reservoirs. Based on our findings, we discuss the larger-scale impacts of cascading hydropower developments and emphasize the need for taking water temperature and its variation into account when developing optimized operation or mitigation strategies for these systems.

scholarly journals Water Temperature and its Diversity in the Deepest Lakes of the Tuchola Forest and the Kashubian and Brodnickie Lakelands

2014 ◽  
Vol 7 (1) ◽  
pp. 105-119 ◽  
Author(s):  
Rajmund Skowron ◽  
Adam Piasecki
Keyword(s):  
Vertical Distribution ◽  
Water Temperature ◽  
Sea Level ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Surface Areas ◽  
The Vertical Distribution ◽  
Depth Water

Abstract This study presents the results of monthly examinations of the vertical distribution of water thermal structure (2008-2011) carried out over a four-year period in the deepest lakes located in the Kashubian and Brodnickie Lakelands and the Tuchola Forest1. Three lakes were selected for examination (Raduńskie Górne, Zbiczno and Ostrowite). Their maximum depths slightly exceed 40 m, and their surface areas range from 121 to 362.5 ha. The results of the measurements show that, despite only minor differences in depth, water temperature varied significantly between the studied lakes. These differences were mainly apparent in the extent of the epilimnion, water thermal stratification, and in the water temperature in the bottom-most layers in summer and winter. The diversity in thermal stratification of the lakes is mainly determined by their morphometric properties, their location above sea level, and the dynamic influences of winds.

scholarly journals Thermal Structure of Water During the Summer in Lakes of the Polish Lowlands as a Result of their Varied Morphometry

2020 ◽  
Vol 20 (2) ◽  
pp. 89-95
Author(s):  
Rajmund Skowron
Keyword(s):  
Water Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Heat Content ◽  
Morphometric Parameters ◽  
Lake Basin ◽  
Structure Of Water ◽  
Basin Morphometry ◽  
The Impact ◽  
The Vertical Distribution

AbstractThe paper discusses the impact of lake morphometric parameters on the thermal structure of water during the period of summer stagnation. The summer period in the lakes is characterized by clearly expressed properties of the thermal structure of water, differentiating lakes from one another. The study was carried out on 141 lakes in northern Poland, for which at least 3 vertical water temperature measurements were taken in different years. They showed a significant influence of lake basin morphometry upon the thermal structure of water in lakes. In general, measurements of the vertical distribution of water temperature showed clear diversity, and depending on the depth also thermal layers (epi-, meta- and hypolimnion). The results of the analysis of 8 lake morphometric parameters and 10 thermal stratification parameters revealed the existence of significant dependencies between them. The best-preserved relations (statistically significant) occurred between the parameters characterizing the lake depth and meta- and hypolimnion properties, as well as the thermal stratification factor and heat content in a unit of volume.

scholarly journals Historical modelling of changes in Lake Erken thermal conditions

2019 ◽  
Author(s):  
Simone Moras ◽  
Ana I. Ayala ◽  
Don C. Pierson
Keyword(s):  
Water Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Time Step ◽  
Entire Interval ◽  
Entire Study ◽  
Study Interval ◽  
Daily Time Step ◽  
Daily Time

Abstract. The thermal structure of lakes is strictly related to climate and to the variability of thermal and mixing dynamics. In this study, a physical hydrodynamic model (GOTM) was used to reconstruct daily time-step water temperature of Lake Erken (Sweden) over the period 1961–2017, using seven climatic parameters as forcing data: wind speed (WS), air temperature (Air T), atmospheric pressure (Air P), relative humidity (RH), cloud cover (CC), precipitation (DP) and shortwave radiation (SWR). The model was calibrated against real water temperature data collected during the study interval, and the calibrated model revealed a good match between modelled and observed temperature (RMSE = 1.112 °C). From the long-term simulations of water temperature, this study focused on detecting possible trends in water temperature over the entire study interval 1961–2017 and in the sub-intervals 1961–1987 and 1988–2017. The analysis of the simulated temperature showed that epilimnetic temperature has increased on average by +0.43 °C/decade and +0.809 °C/decade in spring and autumn in the sub-interval 1988–2017. Summer epilimnetic temperature has increased by +0.348 °C/decade over the entire interval 1961–2017. Hypolimnetic temperature has increased significantly in the sub-interval 1988–2016 by +0.827 °C/decade in autumn. Whole-lake temperature showed a significant increasing trend in the sub-interval 1988–2017 during spring (+0.378 °C/decade) and in autumn (+0.809 °C/decade). Moreover, this study showed that changes in the phenology of thermal stratification, have occurred over the 57-years period of study. Since 1961 the stability of stratification (Schmidt Stability) has increased by 5.535 J m−2/decade. The duration of thermal stratification has increased by 7.083 days/decade, correspondent with an earlier onset of stratification of ~ 16 days and to a delay of stratification termination of ~ 26 days. The average thermocline depth during stratification became shallower by ~ 1.242 m, and surface-bottom temperature difference increased over time by +0.249 °C/decade. The creation of daily-time step water temperature dataset not only provided evidence of changes in Erken thermal structure over the last decades, but it is also a valuable resource of information that can help in future research on the ecology of Lake Erken. The use of readily available meteorological data to reconstruct Lake Erken's past water temperature is shown to be a useful method to evaluate long-term changes in lake thermal structure, and it is a method that can be extended to other lakes.

scholarly journals Historical modelling of changes in Lake Erken thermal conditions

2019 ◽  
Vol 23 (12) ◽  
pp. 5001-5016 ◽  
Author(s):  
Simone Moras ◽  
Ana I. Ayala ◽  
Don C. Pierson
Keyword(s):  
Water Temperature ◽  
Air Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Time Step ◽  
Entire Interval ◽  
Entire Study ◽  
Short Period ◽  
Study Interval

Abstract. Historical lake water temperature records are a valuable source of information to assess the influence of climate change on lake thermal structure. However, in most cases such records span a short period of time and/or are incomplete, providing a less credible assessment of change. In this study, the hydrodynamic GOTM (General Ocean Turbulence Model, a hydrodynamic model configured in lake mode) was used to reconstruct daily profiles of water temperature in Lake Erken (Sweden) over the period 1961–2017 using seven climatic parameters as forcing data: wind speed (WS), air temperature (Air T), atmospheric pressure (Air P), relative humidity (RH), cloud cover (CC), precipitation (DP), and shortwave radiation (SWR). The model was calibrated against observed water temperature data collected during the study interval, and the calibrated model revealed a good match between modelled and observed temperature (RMSE =1.089 ∘C). From the long-term simulations of water temperature, this study focused on detecting possible trends in water temperature over the entire study interval 1961–2017 and in the sub-intervals 1961–1988 and 1989–2017, since an abrupt change in air temperature was detected in 1988. The analysis of the simulated temperature showed that epilimnetic temperature increased on average by 0.444 and 0.792 ∘C per decade in spring and autumn in the sub-interval 1989–2017. Summer epilimnetic temperature increased by 0.351 ∘C per decade over the entire interval 1961–2017. Hypolimnetic temperature increased significantly in spring over the entire interval 1961–2017, by 0.148 and by 0.816 ∘C per decade in autumn in the sub-interval 1989–2016. Whole-lake temperature showed a significant increasing trend in the sub-interval 1989–2017 during spring (0.404 ∘C per decade) and autumn (0.789 ∘C per decade, interval 1989–2016), while a significant trend was detected in summer over the entire study interval 1961–2017 (0.239 ∘C per decade). Moreover, this study showed that changes in the phenology of thermal stratification have occurred over the 57-year period of study. Since 1961, the stability of stratification (Schmidt stability) has increased by 5.365 J m−2 per decade. The duration of thermal stratification has increased by 7.297 d per decade, corresponding to an earlier onset of stratification of ∼16 d and to a delay of stratification termination of ∼26 d. The average thermocline depth during stratification became shallower by ∼1.345 m, and surface-bottom temperature difference increased over time by 0.249 ∘C per decade. The creation of a daily time step water temperature dataset not only provided evidence of changes in Erken thermal structure over the last decades, but is also a valuable resource of information that can help in future research on the ecology of Lake Erken. The use of readily available meteorological data to reconstruct Lake Erken's past water temperature is shown to be a useful method to evaluate long-term changes in lake thermal structure, and it is a method that can be extended to other lakes.

Characteristic of Thermal Structure in Reservoir in Different Climate Zones

2013 ◽  
Vol 807-809 ◽  
pp. 1634-1643 ◽  
Author(s):  
Ding Guo Jiang ◽  
Yu Jing Bie ◽  
Wei Liu
Keyword(s):  
Water Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Water Environment ◽  
Three Dimensional ◽  
Temperature Structure ◽  
Climatic Region ◽  
Reservoir Water ◽  
Discharge Water ◽  
The Impact

A three dimensional mathematical model was used to simulates water temperature structure of a model reservoir under the southwest plateau climate and the subtropics monsoon climate separately. The calculated result shows that: 1. in the Southwest plateau climatic region, obvious double convection was noticed of the surface water, while single convection appears in subtropics monsoon climatic region. 2. Thermal stratification in tropics monsoon climatic region is steadier than the southwest plateau climatic region. 2. In the subtropics monsoon climatic region the water temperature difference between discharge and natural water is more remarkable than the Southwest plateau climatic region, namely that in the subtropics monsoon climatic region the impact of discharge water on downstream water temperature is more appreciable. The research conclusion may provide reference and the basis for the contrastive analysis of related achievement in reservoir water temperature and the water environment.

scholarly journals Spring warming period of Polish lake waters in a yearly thermal cycle

2012 ◽  
Vol 12 (3) ◽  
pp. 147-157 ◽  
Author(s):  
Rajmund Skowron
Keyword(s):  
Surface Water ◽  
Water Temperature ◽  
Thermal Stratification ◽  
Thermal Structure ◽  
Thermal Gradients ◽  
Surface Water Temperature ◽  
Spring Warming ◽  
Warming Period ◽  
Lake Waters ◽  
The Vertical Distribution

AbstractThe study describes thermal regimes of thirty selected Polish lakes in the spring season. The author used 35-year series of daily measurements of surface water temperature in the years 1961-2005 and the measurements of the vertical distribution of water temperature taken in tens of selected water bodies. The diversified pace of the increase in surface water temperature (SWT) during the spring warming period makes it possible to distinguish two thermal phases: the early and late phases of spring warming. The limits of those phases are marked by the dates of the disappearance of ice cover and the dates when the SWT stays well over the threshold values, which amount to 4°C and 15°C respectively. The SWT increase in the lakes (April and May) causes changes in the water’s vertical thermal structure (the formation of epi- and metalimnion) and considerable dynamics of its descriptive parameters, such as water temperature, thermal stratification coefficient, thermal gradients, heat resources, etc.

Development of a water temperature-ecological model to stimulate global warming effects on lake ecosystem

1996 ◽  
Vol 34 (7-8) ◽  
pp. 237-244 ◽  
Author(s):  
Masaaki Hosomi ◽  
Tetsu Saigusa ◽  
Kenichi Yabunaka ◽  
Takuya Okubo ◽  
Akihiko Murakami
Keyword(s):  
Global Warming ◽  
Water Temperature ◽  
Thermal Stratification ◽  
Ecological Model ◽  
Nutrient Release ◽  
Eddy Diffusion ◽  
Nutrient Concentrations ◽  
Lake Ecosystem ◽  
Phytoplankton Species ◽  
Freezing And Thawing

This paper describes a newly developed combined water temperature-ecological (WT-ECO) model which is employed to simulate the effects of global warming on lake and reservoir ecosystems. The WT model includes (i) variations in the eddy diffusion coefficient based on the degree of thermal stratification and the velocity of wind, and (ii) a sub-model for simulating the freezing and thawing processes of surface water, water temperatures, and the mixing rates between two adjacent layers of water. The ECO model then uses these results to calculate the resultant effect on a lake's ecological dynamics, e.g., composition of phytoplankton species, their respective concentrations, and nutrient concentrations. When the model was benchmarked against Lake Yunoko, a dimictic lake, fairly good agreement was obtained over a 4-yr period; thereby indicating it is suitably calibrated. In addition, to assess the effects of global warming on a lake ecosystem, changes in Lake Yunoko's water temperature/quality were simulated in response to an increase in air temperature of 2 - 4°C. Results indicate that such an increase will (i) increase thermal stratification in summer, which increases the nutrient concentrations in bottom water due to nutrient release from bottom sediment, (ii) increase the concentration of phytoplankton at the beginning of the autumn circulation period, and (iii) change the composition of phytoplankton species.

scholarly journals Twentieth-Century Climate Change over Africa: Seasonal Hydroclimate Trends and Sahara Desert Expansion

2018 ◽  
Vol 31 (9) ◽  
pp. 3349-3370 ◽  
Author(s):  
Natalie Thomas ◽  
Sumant Nigam
Keyword(s):  
Twentieth Century ◽  
Source Region ◽  
Surface Air Temperature ◽  
Rain Gauge ◽  
Mitigation Strategies ◽  
Annual Rainfall ◽  
Sahara Desert ◽  
Seasonal Temperature ◽  
African Continent ◽  
Climate Simulations

Twentieth-century trends in seasonal temperature and precipitation over the African continent are analyzed from observational datasets and historical climate simulations. Given the agricultural economy of the continent, a seasonal perspective is adopted as it is more pertinent than an annual-average one, which can mask offsetting but agriculturally sensitive seasonal hydroclimate variations. Examination of linear trends in seasonal surface air temperature (SAT) shows that heat stress has increased in several regions, including Sudan and northern Africa where the largest SAT trends occur in the warm season. Broadly speaking, the northern continent has warmed more than the southern one in all seasons. Precipitation trends are varied but notable declining trends are found in the countries along the Gulf of Guinea, especially in the source region of the Niger River in West Africa, and in the Congo River basin. Rainfall over the African Great Lakes—one of the largest freshwater repositories—has, however, increased. It is shown that the Sahara Desert has expanded significantly over the twentieth century, by 11%–18% depending on the season, and by 10% when defined using annual rainfall. The expansion rate is sensitively dependent on the analysis period in view of the multidecadal periods of desert expansion (including from the drying of the Sahel in the 1950s–80s) and contraction in the 1902–2013 record, and the stability of the rain gauge network. The desert expanded southward in summer, reflecting retreat of the northern edge of the Sahel rainfall belt, and to the north in winter, indicating potential impact of the widening of the tropics. Specific mechanisms for the expansion are investigated. Finally, this observational analysis is used to evaluate the state-of-the-art climate simulations from a comparison of the twentieth-century hydroclimate trends. The evaluation shows that modeling regional hydroclimate change over the African continent remains challenging, warranting caution in the development of adaptation and mitigation strategies.

scholarly journals Evolution of the seasonal temperature cycle in a transient Holocene simulation: orbital forcing and sea-ice

2011 ◽  
Vol 7 (1) ◽  
pp. 463-483 ◽  
Author(s):  
N. Fischer ◽  
J. H. Jungclaus
Keyword(s):  
Sea Ice ◽  
Arctic Ocean ◽  
The Arctic ◽  
Northern Europe ◽  
Temperature Cycle ◽  
Surface Model ◽  
Seasonal Temperature ◽  
Ice Dynamics ◽  
Summer Insolation ◽  
The Arctic Ocean

Abstract. Changes in the Earth's orbit lead to changes in the seasonal and meridional distribution of insolation. We quantify the influence of orbitally induced changes on the seasonal temperature cycle in a transient simulation of the last 6000 years – from the mid-Holocene to today – using a coupled atmosphere-ocean general circulation model (ECHAM5/MPI-OM) including a land surface model (JSBACH). The seasonal temperature cycle responds directly to the insolation changes almost everywhere. In the Northern Hemisphere, its amplitude decreases according to an increase in winter insolation and a decrease in summer insolation. In the Southern Hemisphere, the opposite is true. Over the Arctic Ocean, however, decreasing summer insolation leads to an increase of sea-ice cover. The insulating effect of sea ice between the ocean and the atmosphere favors more continental conditions over the Arctic Ocean in winter, resulting in strongly decreasing temperatures. Consequently, there are two competing effects: the direct response to insolation changes and a sea-ice dynamics feedback. The sea-ice feedback is stronger, and thus an increase in the amplitude of the seasonal cycle over the Arctic Ocean occurs. This increase is strongest over the Barents Shelf and influences the temperature response over northern Europe. We compare our modelled seasonal temperatures over Europe to paleo reconstructions. We find better agreements in winter temperatures than in summer temperatures and better agreements in northern Europe than in southern Europe, since the model does not reproduce the southern European Holocene summer cooling inferred from the paleo data. The temperature reconstructions for northern Europe support the notion of the influence of the sea-ice effect on the evolution of the seasonal temperature cycle.

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