A complex network analysis of Spanish river basins

Abstract

This paper carries out a study of Spanish river basins for the period 2008–2014 using complex network analysis (CNA) tools. The purpose is to gain insight into the structure and characteristics of the national hydrological system with an emphasis on the interconnectivity between the different river basins and the extent to which the current IBT can mitigate the rainfall imbalances of the country, particularly in a scenario of climate change. Apart from the size of the corresponding catchment areas, data on water demand for irrigation, industrial and municipal water supply, historical catchment inflows, reservoir capacity and historical levels, interbasin transfer infrastructures and historical interbasin transfer (IBT) flows, and ocean discharges were collected. A weighted directed network is built with all this information and a number of CNA characterization measures. It has been found that the system has a two-tier structure with a few river basins (hubs) that supply IBT flows to a relatively large number of receiver river basins. Some of those receiver river basins have incoming links from more than one source river basin. This diversification of IBT sourcing is necessary since the availability of water for IBT from a single river basin is not guaranteed. The CNA results also indicate that the IBT infrastructure has been designed to supply water from the river basins with surplus reservoir capacity to river basins with water deficits. The community structure of the system has also been determined with some groups of river basins forming separate, self-sufficient subsystems and other communities minimally connected by IBT links. It can be concluded that the topology and characteristics of the network are a consequence of the imbalances created by the varying climatic conditions of the river basins, the water storage capacity provided by the existing reservoir infrastructure, the geographical and orographic constraints of the country and the high cost of establishing links between neighbouring river basins.