Urban green spaces are often promoted as nature-based solutions, thus helping to mitigate the negative effects of climate change. Estimating the potential environmental benefits provided by urban green space is difficult because of inconsistencies in management practices and their heterogeneous nature. Collecting data across such a spectrum of contexts at a large scale is costly and time consuming. In this study, we explore a novel integrated method for citizen scientists to assess the flood mitigation potential of urban green spaces. In three European cities, citizen scientists measured infiltration rate and associated soil characteristics in managed and unmanaged urban green spaces. The results show that simple citizen science-based measurements can indicate the infiltration potential (i.e., high vs. low) of soil at these sites. Infiltration rate was best predicted by measurements of soil compaction, soil color, air temperature, and level of insolation (i.e., high vs. low). These simple, fast methods can be repeated over time and space by citizen scientists to provide robust estimates of soil characteristics and the infiltration potential of soils that exist in similar temperate urban areas. A classification flow diagram was constructed and validated that allows citizen scientists to carry out such tests over a wider geographical region and at a higher frequency than would be available to research scientists alone. Most importantly, it allows citizens to take actions to improve infiltration in their local green space and support local flood resilience.

Trophic cascades in the aquatic environment constitute important mechanisms for improving water quality. However, how the presence or non-presence of these trophic cascades may affect interactions across the aquatic-terrestrial interface remains poorly investigated. Pollinators such as bees may be especially vulnerable to changes in water resource quality induced by trophic cascades. Understanding how aquatic trophic cascades affect bees and pollination becomes even more pressing under ongoing climate change due to increased physiological demands for water under extreme weather events. In a novel field experiment combining terrestrial and aquatic mesocosms, we aimed to test how changes in water quality induced by an aquatic trophic cascade affected foraging and growth of bumblebee colonies as well as foraging of solitary bees. While we expected fish predation to reduce top-down control of zooplankton on phytoplankton and thereby, indirectly, induce increased growth of toxic cyanobacteria, we instead found the trophic cascade to induce the formation of algal surface mats that bumblebees used to access water under a severe heat wave and drought. This access to water was associated with higher bumblebee colony reproductive success, growth and weight compared to control colonies with no trophic cascade induced (and hence no algal surface mats). We also found marginal but non-significant effects on oilseed rape yield, but surprisingly with higher yields in the control treatment where bumblebees could not access water. Our results provide new insights on how aquatic trophic cascades can lead to unpredicted ecological interactions across the aquatic-terrestrial interface facilitated by climate change. Our study highlights the importance of water for the fitness of terrestrial ecosystem service providers under altered environmental conditions.