179 / 2024-02-26 20:02:35

Spatiotemporal Variation Characteristics of Water Temperature in the Lower Reaches of the Jinsha River under the Joint Operation of Four-level Cascade Reservoirs

Lower reaches of the Jinsha River; Water temperature; Spatiotemporal Variation; Cascade reservoirs;

After the joint operation of four-level cascade reservoirs in the lower reaches of the Jinsha River, the downstream now encounters a novel thermal regime, however, the current understanding of this regime remains incomplete. This study utilizes measured long-term observed data, focusing on baseline temperature deviation, phase deviation, cumulative frequency and extreme value range to quantitatively analyze the spatiotemporal variation characteristics of water temperature of the cascade reservoirs in the lower Jinsha River. The purpose of this study was to comprehensively explore the propagation patterns and potential accumulations of temperature along the cascade reservoirs. The results indicated that due to the combined influences of climate warming and the operation of cascade reservoirs, the annual average discharge temperatures of each reservoir in the lower reaches of the Jinsha River are gradually increasing. Delay and homogenization effects are noticeable. The water temperature exhibits distinct diurnal variations with a maximum difference of up to 5.9°C, attributed to the influence of daily reservoir regulation. Among the reservoirs, the Wudongde reservoir does not exhibit thermal stratification, while the Baihetan, Xiluodu, and Xiangjiaba reservoir areas show seasonal thermal stratification. However, with the increasing operation time of cascade reservoirs, the vertical temperature gradient decreases, the thermal stratification weakens, but the effects of temperature fluctuations significantly enhance. The cumulative frequency of temperature for each reservoir is 0.77, 0.78, 0.64, and 0.73, respectively, with the temperature rise congestion effect being significantly higher than the temperature decrease congestion effect. The construction of cascade reservoirs disrupts the continuity of water temperature, leading to noticeable differences in water temperatures between the upstream and downstream of the reservoirs, with a maximum difference of up to 4.3°C. The high-density development of cascade reservoirs also intensifies the spatial cumulative effect of water temperature, particularly evident at the terminal reservoir, Xiangjiaba, where the cumulative temperature effect is notably pronounced. Our findings provide crucial scientific insights for future basin-scale temperature management and optimization of cascade reservoir operations.