Urban gardens in Central California are highly exposed to the effects of climate change, experiencing both extended high heat periods as well as water restrictions because of severe drought conditions. This puts these important community based food production systems at risk as California is expected to experience increasing weather extremes. Evidence from agricultural systems has shown that increased vegetation complexity, such as greater structure or biodiversity, can increase the resilience of food production systems from climate fluctuations. In this study, we look at both local and landscape scale factors of vegetation cover to better understand what is driving the microclimate of these gardens and how this may affect water use of gardeners.
Twenty-five urban gardens were selected in the Central Coast region of California within Santa Clara, Santa Cruz, and Monterrey County. Within the gardens, descriptive information such as garden size and local vegetative characteristics were collected. On the landscape scale, data from the National Land Cover Database were used to measure different land cover classes within a 5km radius from each garden. Onset climate loggers were established in each garden throughout the summer of 2016 in order to record temperatures at 30 minute increments.
Multivariate analyses were conducted to examine the effect of local and landscape scale factors on garden microclimate. Results show that county and % mulch cover are strong predictors for mean temperature, with the addition of garden size significant for maximum temperature. Santa Clara County exhibited higher temperatures than the other two counties; garden size was correlated with higher maximum temperatures; and greater mulch coverage was correlated with lower temperatures. Regionally, the % cover of water, urban, and grasslands had a significant effect on mean temperature with % water cover reducing temperatures, while urban and grassland cover increased temperatures. % cover of wetland and water in region were correlated with reduced maximum temperatures.
Analysis of gardener watering behaviour shows both mean and maximum temperatures were highly correlated with the number of minutes as well as the number of liters of water used per watering event. These results indicate that gardeners are sensitive to climate and can affect watering behaviour. Although it may be difficult to manage for landscape scale factors, understanding the effect that the landscape has on garden microclimate can assist managers in adopting local management actions, such as increasing mulch cover, to reduce garden microclimate, and thus reduce water use.