What indicators can capture runoff-relevant connectivity properties of the micro-topography at the plot scale?

Although connectivity is acknowledged as a key factor of a catchment hydrological behaviour, it still misses reference evaluation methodologies. Therefore the objective of the paper is to evaluate different quantitative indicators of hydrological connectivity, using the concepts of structural and functional connectivity commonly used in ecology. The indicators were tested on contrasted numerical fields of micro-topography that present distinct hydrological responses.The investigated structural connectivity indicators, mostly used so far in porous or fractured media, were the semivariogram, the bivariate entropy integral scale, the n-point rectilinear connectivity integral scale, the connectivity function integral scale, the percolation threshold and the Euler number. The first three indicators were not able to discriminate between the three extreme types of micro-topographical fields whereas the last three indicators were successful. However, relating the latter three indicators to the hydrological response of a topographical field appears uncertain. We therefore proposed a functional connectivity indicator by adapting the ‘volume to breakthrough’ concept: the degree of surface connection as a function of the surface storage filling. This indicator was capable of discriminating between the micro-topographical types. It could be used to conceptualize the process of depression filling and therefore may become an effective characteristic of an elementary representative area in large scale hydrologic model.