This book provides a state of the art overview of rainfall nowcasting or short-term rainfall forecasting, which is an essential component of early warning systems for mitigating risks of landslide and floods. Special attention is given to spatial and temporal hydrological scales that are associated with the forecast of flash-floods and shallow-landslides. The importance of Probabilistic Quantitative Precipitation Forecast (PQPF) is highlighted. This approach is beneficial to a Quantitative Precipitation Forecast (QPF). Moreover, several approaches for nowcasting are compared. In particular, the differences in performances between stochastic and meteorological models. A methodology for coupling these approaches is proposed, which can improve nowcasting "outside a storm event" (ie: prior to the commencement of rainfall).