Toward An Assessment of Runoff and Thermal Connectivity in A River-Lake System within An Urban Environment

Abstract

The term ‘hydrological connectivity’ is used in different disciplines to refer to the water-mediated transfer of matter, energy, and/or organisms within or between elements of the hydrologic cycle. Extensive research has been devoted to methods of evaluating hydrological connectivity. However, most of these methods pertain to the connectivity of runoff, sediment, chemicals, and organisms. To our knowledge, no evaluation of thermal energy connectivity has been conducted to date, and there is no consistent assessment framework available that takes into account thermal energy connectivity based on flux. Thermal energy flux affects many basic biogeochemical reaction processes and ecological functions of healthy river-lake systems. Here, we propose a method to evaluate runoff and thermal connectivity based on a modified version of the index of runoff/sediment connectivity proposed by Borselli et al. (2008). It was tested in an urban area (Tongling, China, which covers an area of 3008 km2) — characterized by the presence of numerous rivers and lakes — during normal, wet, and dry periods from year 2016 to year 2018. We found that areas with poor runoff connectivity exhibited high thermal connectivity in dry periods. Connectivity variation in lakes was higher than that in rivers. Models of the measured data were satisfactory for the test periods. Overall, our results indicate that public data can be used to map runoff and thermal connectivity within an existing joint evaluation framework. Evaluations of thermal connectivity can assist research on hydrological connectivity, and the proposed method can serve as a valuable tool for analyzing the runoff and thermal connectivity of urban river-lake systems.

Keywords: hydrological connectivity, runoff flux, thermal flux, river-lake system, spatial pattern, urbanization, impervious area