Shi Lidi, Morovati Khosro, Sun Jian, Lin Binliang, Zuo Xinyu
State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing, 100084, China.
Upper Changjiang River Bureau of Hydrological and Water Resources Survey, Chongqing, 400025, China.
Environ Monit Assess. 2023 Jan 26;195(2):334. doi: 10.1007/s10661-023-10948-w.
The thermal regime in large reservoirs plays a significant role in the water quality and ecosystem succession; however, little is known about the impacts of regional climate changes and hydrological conditions on a sizeable stratified reservoir with strong inflow conditions, i.e., the Xiangjiaba Reservoir. Using measured data from 2014 to 2018, the monthly and seasonal variations of the water temperature, thermal stability, and their influencing factors were addressed by using empirical models. The results showed substantial variability and seasonality in the reservoir water temperature, which correlated highly with the air temperature, inflow water temperature, and discharge. Correspondingly, there was a seasonal varying thermal stratification in the reservoir's yearly cycle, with its duration being up to 4 ~ 5 months, the maximum surface-bottom water temperature difference being up to 7 ~ 10 °C. There were significant positive correlations between Schmidt's stability index of the thermal structure and inflow-reservoir temperature difference and the surface-bottom temperature differences, while negative correlations with large discharge. Moreover, the inflow tends to influence thermal stability by retaining hypolimnion cold water, with its maximum bottom hysteresis residence time being up to ~ 4 months. Research findings indicated that climate warming in the recent 30 years (1988 ~ 2017) would cause a 0.213 °C/decade and 0.153 kJ/m/decade increase in reservoir surface water temperature and Schmidt's stability index, respectively. Among these variations, the inflow temperature increase caused by climate change accounted for the largest proportion, i.e., 0.16 °C/decade and 0.115 kJ/m/decade. Therefore, climate warming significantly affected the thermal regimes in this large reservoir, and the inflow water temperature increase due to warm air was the main factor altering the reservoir's thermal structure. Findings from the present study provide a fresh perspective on how to best optimize the deep channel-type reservoirs' water quality in the face of anticipated climate change.
大型水库的热状况对水质和生态系统演替起着重要作用；然而，对于区域气候变化和水文条件对具有强入流条件的大型分层水库（即向家坝水库）的影响，人们了解甚少。利用2014年至2018年的实测数据，通过经验模型研究了水温、热稳定性的月变化和季节变化及其影响因素。结果表明，水库水温存在显著的变异性和季节性，与气温、入库水温及流量高度相关。相应地，水库年周期内存在季节性变化的热分层，其持续时间长达4至5个月，表层与底层水温最大差值可达7至10℃。热结构的施密特稳定性指数与入库-水库温差及表层-底层温差呈显著正相关，与大流量呈负相关。此外，入流倾向于通过保留下层冷水来影响热稳定性，其最大底部滞后停留时间可达约4个月。研究结果表明，近30年（1988至2017年）的气候变暖将导致水库表层水温分别以0.213℃/十年和施密特稳定性指数以0.153kJ/m/十年的速度增加。在这些变化中，气候变化导致的入库水温升高占比最大，即0.16℃/十年和0.115kJ/m/十年。因此，气候变暖显著影响了这座大型水库的热状况，暖空气导致的入库水温升高是改变水库热结构的主要因素。本研究结果为面对预期气候变化时如何最佳优化深槽型水库水质提供了新的视角。
