Assessment of the rainfall-runoff relationships

Runoff is defined here as the part of precipitation that appears as streamflow. The generation processes are widely described in literature (e.g. Newson, 1995 ; Brooks et al. , 1997 ; Bonell, 1998 ; Beven, 2001b ; Uhlenbrook, 2005 ). Precipitation is viewed as the major input to a catchment and a key to its water yield characteristics. Besides precipitation, evapotranspiration is in general the most significant hydrological factor that determines runoff generation. The dynamics of hydrological processes are driven by meteorological factors, but the changes that these factors cause for the discharge regime do not occur instantaneously ( WMO, 1994 ). The non-linear and time-variant nature of the relation between precipitation and runoff makes it difficult determining and quantifying changes in the relationship. Moreover, the derivation of the rainfall-runoff relationship over a catchment is very much dependent on the time scale (being considered) and is also affected by the spatial scale being considered ( Shaw, 1991 ; Blöschl and Sivapalan, 1995 ).