Adaptation to a changing climate is unavoidable. Mainstreaming climate adaptation objectives into existing policies, as opposed to developing dedicated adaptation policy, is widely advocated for public action. However, knowledge on what makes mainstreaming effective is scarce and fragmented. Against this background, this paper takes stock of peer-reviewed empirical analyses of climate adaptation mainstreaming, in order to assess current achievements and identify the critical factors that render mainstreaming effective. The results show that although in most cases adaptation policy outputs are identified, only in a minority of cases this translates into policy outcomes. This “implementation gap” is most strongly seen in developing countries. However, when it comes to the effectiveness of outcomes, we found no difference across countries. We conclude that more explicit definitions and unified frameworks for adaptation mainstreaming research are required to allow for future research syntheses and well-informed policy recommendations.

Climate change is associated with various risks, such as flooding and heat stress. So far, most research has concentrated on the identification and quantification of these risks as well as the development of adaptation measures. Yet much less is known about how planners actually perceive and deal with climate change, and why. This paper focuses on the governance of two climate change-related risks in urban areas in the Netherlands, namely heat stress and flooding from rainfall and rivers. Heat stress hardly seems to be perceived as an urgent problem, mainly because there is no clear ‘problem owner’. Because municipalities are responsible for rain and sewage water management and partly for river flooding, increased flood risk is more often recognised as a (potential) problem. Despite the rather low sense of urgency regarding these two climate change-induced risks, urban planners are, or envisage, investing in more open water and public green areas. Heat stress and flood risks from rainfall are not the reasons per se, but primarily act as additional arguments to legitimise these measures, which should contribute to sustainable urban development in general. Our analysis suggests a gap between the perceived urgency of proactive adaptation to climate change by scientists and the perceptions of planners. Climate science research could enhance its contribution to urban planning by providing conceivable projections of climate change impacts as well as by developing adaptation measures that serve multiple purposes and strategies to successfully implement these.