A framework for assessing river thermal regime alteration: A case study of the Hanjiang River

Abstract

To better understand the river thermal regime alteration caused by anthropogenic disturbances, we propose a framework to assess the alteration degree of thermal regime in a regulated river. In this framework, 23 temperature metrics including existing and newly developed temperature parameters, are used to characterize river thermal alteration and are organized into four groups, i.e., Magnitude, Timing, Variability, duration and frequency. The proposed framework is then applied to assess the impacts of the Danjiangkou Dam on the thermal regime of the Hanjiang River. Our results show that the Danjiangkou Dam had a substantial impact on the thermal regime of the Hanjiang River by increasing water temperature in winter and decreasing water temperature in spring and summer, especially after the dam was raised. The effect was greatest immediately downstream to the dam, and decreased with as the distance from the dam increases. Start date of the critical 18℃ was delayed by approximately two months. Such effects may lead to negative ecological implications to the downstream of the Danjiangkou Dam. The results of this study illustrate the pronounced effect of the Danjiangkou Dam on the thermal regime of the Hanjiang River. The framework proposed could be a robust method to assess the impacts of reservoir operation on the thermal regime for regulated rivers.