It is widely predicted that regional precipitation patterns may be altered due to climate change, and these changes may affect areas with extensive forests. Therefore, studies investigating the role of this climate driver on forest floor fauna are timely. We examined the impact of precipitation alteration over 13 years on Coleoptera (specifically Family Carabidae) communities in a temperate forest by testing the effects of dry (33% precipitation interception), ambient (control), and wet (33% precipitation addition) treatments. We collected insects in pitfall traps and quantified forest-floor physical and chemical parameters. Beetle abundance and Carabidae tribe richness were significantly reduced in dry plots. Community similarity was substantially higher between wet and ambient plots compared to dry plots due to the substantial reduction of three dominant carabid tribes. Litter mass increased overall, litter nitrogen decreased, and carbon:nitrogen ratio (C:N) and total phenolics increased in the dry-plot Oi horizon. Beetle abundance and tribe richness were positively related to soil moisture, and beetle abundance was negatively related to litter mass. Microarthropod abundance was highest in the dry treatment. This study provides evidence that shifting precipitation patterns predicted with climate change could alter important ground-fauna communities in extensive ecosystems such as temperate forests.