Heatwaves and Rising Temperatures in the Upper San Francisco Estuary: Trends and Effects on Ecosystems and Humans

Rising temperature is one direct consequence of climate change, and temperature is a key controlling variable on biological processes from molecular to ecosystem scales. While rising average temperature is one of the most discussed aspects of climate change, extreme events such as heatwaves are also expected to increase in duration, intensity, and frequency. These changes will bring about effects that threaten the integrity of the upper San Francisco Estuary (estuary) ecosystem, the services they provide to humans, and the health of humans that reside in the region. In the estuary, warmer temperatures are expected to result in seasonal shifts to life-cycle timing, and to favor smaller-bodied individuals across most non-human taxa. Several native fish species will likely decline, while a considerable number of non-native and cosmopolitan species tolerant of high temperatures are predicted to be relatively unaffected by or even benefit from a warmer climate. For humans, high temperatures and heatwaves are associated with wide-ranging health effects, from direct effects such as dehydration and heat exhaustion, to indirect and adverse health outcomes such as lower birth weight, mental health problems, and violence. These health effects will be exacerbated by ecosystem changes, as a longer warm season will increase our exposure to vectors such as mosquitos, as well as to the toxins produced by harmful algal blooms. Climate change is a global issue that cannot be resolved effectively at a regional level; however, some actions can either be taken or further studied to potentially lessen the effects of rising temperatures for the estuary’s ecosystem and residents at a more localized level. Although decreasing global greenhouse gas emissions remains our best option to combat climate change and the resultant temperature increases, successful adaptation to warming and heatwaves will require actions at multiple scales.