Introducing drought-tolerant groundcovers into urban landscapes can enhance evaporative cooling while reducing irrigation demand in semiarid and arid regions. A two-year field experiment (2022-2023) conducted in Riverside, California, evaluated the responses of four groundcover species-Acacia redolens, Arctotis acaulis, Chrysanthemoides incana, and Lippia nodiflora-to four irrigation levels (25-100 % reference evapotranspiration, ET0). Normalized difference vegetation index (NDVI), visual quality, and the canopy and air temperature difference (Delta T) were monitored across treatments. The calibrated HYDRUS-1D model simulated soil water content (SWC) and actual transpiration (Ta) for each treatment, which were used to develop regression-based water response function (WRF) models for estimating NDVI and Delta T. Acacia redolens provided the greatest potential evaporative cooling effect, with mean Delta T ranging from-3.99 to-5.86 degrees C across irrigation levels, while maintaining high aesthetic quality even at 25 % ET0. In contrast, Lippia nodiflora required at least 51 % ET0 irrigation to sustain acceptable visual quality and 100 % ET0 to maintain a cool canopy. The strongest correlation between NDVI and HYDRUS-1D outputs was observed for Lippia nodiflora (r = 0.68-0.80). Delta T for all ground-covers showed a relatively strong correlation with simulated Ta (r =-0.59 to-0.71), and incorporating model outputs into WRFs improved Delta T prediction accuracy (r = 0.64-0.80). These results highlight Acacia redolens as a climate-resilient and water-efficient groundcover, offering substantial cooling and aesthetic performance under minimal irrigation. The findings of this study can inform urban landscape design, irrigation management strategies, and green infrastructure planning in water-limited regions.