Rainfall-Runoff Models：降雨径流模型.ppt

BEGIN Rainfall-Runoff Models Excess Precipitation or Runoff Volume Models May be: Physically Based Empirical Descriptive Conceptual Generally Lumped Etc…… May not only estimate excess precipitation – hence, we will refer to them as rainfall-runoff models….. The Basic Process…. Goal of Rainfall-Runoff Models The fate of the falling precipitation is: …modeled in order to account for the destiny of the precipitation that falls and the potential of the precipitation to affect the the runoff hydrograph. … losses include interception, evapotranspiration, storage, infiltration, percolation, and finally - runoff. Let’s look at the fate of the precipitation….. Interception........... Canopy…(or lack of) Leafy Matter also intercepts... Interception…the point The point of the interception is that the precipitation is temporarily stored before the next process begins. The intercepted/stored precipitation may not reach the ground to contribute to runoff. Interception may be referred to as an abstraction and is accounted for as initial abstraction in some models. This is also true for snowfall which may sublimate and leave the watershed! Infiltration........... Infiltration, cont........... Percolation..... Percolation..... Percolation..... Percolation….the point The vertical percolation of the water into various levels or zones allows for storage in the subsurface – these zones will be very important in the SAC-SMA model. This stored subsurface water is held and released as either evaporation, transpiration, or as streamflow eventually reaching the watershed outlet. Evaporation.... Transpiration.... Evapotranspiration.... Storage.... Storage.... Storage.... Storage.... Things to consider: We looked at these as independent processes! We looked at the processes as discrete time steps! What were the initial conditions before the storm? What effects would initial conditions have? These are the issues that a continuous rainfall-runoff model must consider…… The Units The unit