Soil moisture drydown patterns encode signatures of plant water use. Previous characterizations of the drydown patterns assume a static linear relationship between water-limited transpiration and available moisture. However, ecohydrological studies show that plants exhibit a spectrum of responses to water availability, suggesting that soil moisture loss functions may be nonlinear. To represent these dynamics, we introduce a nonlinearity parameter to the loss function. Our analysis shows that the nonlinear loss model improves the characterization of the satellite-observed soil moisture drydowns. Globally, functional responses of drydowns are dominated by convex nonlinearity, showing greater declines in water use in dry soils than the linear loss function predicts. We find distinct degrees of nonlinearity among different vegetation types; areas with non-woody vegetation more frequently exhibit a concave nonlinearity, the signature of aggressive water-use strategies. We propose the nonlinear loss function as continuous and dynamic representations of plant water-use strategies under changing water availability.