On the relations between critical behaviour of soil moisture spatio-temporal dynamics and catchment descriptors

When changing from spatially random to spatially connected appearances as conditions become wetter in their seasonal time dynamics, soil moisture spatial patterns show a behaviour similar to phase transition processes. In a previous work, once implemented an ad-hoc methodology, we have demonstrated that such a phase change shows critical point behaviour. Moreover, the value of the critical probability seems to be an intrinsic characteristic of a catchment, being insensitive to renormalization (rescaling), as well as to model parameterization.Working on a set of simulated daily soil moisture maps for 20 selected sub-catchments of the Red and Arkansas basins in the south-central United States, we extract the critical point and we compare its value to several morphologic indices of the catchments, such as bifurcation and elongation ratios, informational entropy, and the exponent of the power law distribution of areas.The relations between critical point and morphological indices seem to be affected by both hillslope and channel network morphological structures. The organization of soil moisture, as assessed by the critical point value, and of channel network should grow simultaneously. Whether factors disturbing the hillslope development occurred, they would cause a departure in such trend.Critical point could represent an integrated measure of catchments' organization.

Research Highlights
► The soil moisture dynamics at the catchment scale show critical point behaviour.
► The critical point value is lower for basins with organized morphological structures.
► The critical point represents a measure of the organization at the hillslope scale.
► The coupling of river network and hillslope morphology is not mutual.
► Critical point could represent an integrated measure of catchments' organization.