Introduction

Temperatures are increasing worldwide, and urban ecosystems are warming faster than other ecosystems due to the urban heat island effect (Wilby 2008; IPCC 2021). Urban waterbodies (i.e., permanent sources of static or flowing water) can mitigate urban heat, and therefore serve as important cooling islands (Murakawa et al. 1991; Hathway and Sharples 2012; Sun et al. 2012; Xue et al. 2019). Urban waterbodies also support biodiversity and provide cultural ecosystems services (reviewed in Hassall 2014; Alikhani et al. 2021). Riparian areas, including those in urban drylands, are particularly important for preserving biodiversity (Naiman and Décamps 1997; Trammell et al. 2011; McCluney and Sabo 2014; Banville et al. 2017; García-Martínez et al. 2017; Ramey and Richardson 2017). In the absence of sufficient precipitation, urban rivers allow terrestrial organisms to access water, a vital resource that is becoming increasingly scarce in many regions due to climate change (Trenberth 2011; Sarhadi et al. 2018; Giorgi et al. 2019; IPCC 2021). Thus, proximity to a river can represent a gradient of resource availability for organisms. Although access to a water source offers advantages (Chamaillé-Jammes et al. 2007; Chen et al. 2015), such high-resource environments may have drawbacks, including increased competition (Kotowski et al. 2006; Pafilis et al. 2009; Laliberté et al. 2013) or predation risk (reviewed in Yuen and Dudgeon 2015).

Precipitation is a strong selective force on terrestrial plants and animals worldwide (Siepielski et al. 2017). It may also modulate the costs and benefits of permanent water sources to organisms whereby the relative value of a permanent water source is reduced by precipitation. Precipitation often varies seasonally, and seasonal climate patterns of precipitation and temperature can synergistically interact to modify the role of permanent water sources to organisms. For example, Mediterranean climates are found across several continents, and they exhibit an inverse relationship between temperature and precipitation (i.e., dry summers and wet winters: Kottek et al. 2006; Stahle et al. 2020). Here, close proximity to a river or pond may have a greater effect on community dynamics during a hot, dry summer than during a cool, wet winter. Yet, the interactive effects of water’s spatial and temporal availability (i.e., proximity to a permanent water source and seasonal precipitation patterns, respectively) on animal communities are not fully understood (but see Yuen and Dudgeon 2015; McCluney et al. 2018).

The biomass and biodiversity of communities are key ecological indicators, and they are related to one another in many communities. For example, the relationship between plant biomass and biodiversity may be positive (reviewed in Wu et al. 2012; 2014), particularly in urban areas, may provide important insight into how insect communities (and the ecosystems they service) respond to the world’s future climate.