Abstract
Abstract We monitored lake surface water temperatures from 1992 to 2019 in Lake Kasumigaura, a shallow lake in Japan. We hypothesized that increases of shortwave radiation had increased surface water temperatures and heat fluxes more than had the increases of air temperature. We used the heat flux analyses and the sensitivity analyses to test the hypothesis. The fluxes of solar radiation gradually increased during the study period in a manner consistent with the phenomenon of global brightening. The increase was especially apparent in the spring. The rate of increase of surface water temperature was especially significant in May. Air temperature did not significantly increase in May, but it increased significantly in June (0.40 °C decade−1). A sensitivity analysis of the heat fluxes at the lake surface (shortwave radiation, longwave radiation, latent heat flux, and sensible heat flux) revealed that surface water temperature was more sensitive to changes of shortwave radiation than to air temperature during the spring. Although other factors such as inflows of groundwater and river water may also have impacted surface water temperatures, the increase of solar radiation appeared to be the major factor responsible for the increase of surface water temperature during the spring in Lake Kasumigaura.
Highlights
The International Panel on Climate Change (IPCC) has predicted a global temperature increase of 4.8 °C by 2100 based on scenario RCP 8.0 (Stocker et al 2013)
Global air temperature increase could cause an increase of surface water temperatures, but some studies have already reported that the rate of increase of surface water temperatures has exceeded the rate of increase of air temperature in lakes (Schmid & Köster 2016; Woolway et al 2019)
The higher rate of increase of surface water temperature than air temperature was consistent with results of previous studies (Li et al 2019), and the increase of surface water temperature in spring was consistent with previous studies in shallow lakes in China (Li et al 2019)
Summary
The International Panel on Climate Change (IPCC) has predicted a global temperature increase of 4.8 °C by 2100 based on scenario RCP 8.0 (Stocker et al 2013). This increase in air temperature could substantially affect lacustrine environments (Woolway et al 2020). Previous studies have experimentally predicted the effects of increases of surface water temperatures on aquatic ecosystems (Meerhoff et al 2012; O’Reilly et al 2015), such as macrophytes (Feuchtmayr et al 2009) and phytoplankton blooms (Bucak et al 2018).
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