Hydrological Connectivity Does Change Over 70 Years of Abandonment and Afforestation in the Spanish Pyrenees

Abstract

Runoff connectivity depends on topography, rainfall, man-made elements (terraces, trails, roads and drainage systems) and vegetation. In this study, we quantified the effects of 70 years of human activities on runoff connectivity in the mountainous Araguás afforested sub-catchment (17·2 ha; Central Spanish Pyrenees). The IC index of hydrological connectivity was chosen to perform this metric over six land use scenarios at high spatial resolution (1 × 1 m of cell size). The current scenario (year 2012) was simulated with three flow accumulation algorithms (MD, MD8 and D8). MD8 was linked with the most frequent hydrological response of the sub-catchment (rainfall intensity and stream flow during 7 years) and generated the most representative pattern of connectivity, especially in the linear landscape elements (LLE). This algorithm was chosen to simulate five past scenarios (1945, 1956, 1973, 1980 and 2006). In all scenarios, the highest connectivity appeared related to trails and roads, as well as to streams and gullies, whereas the lowest appeared related to stonewalls in 1945 and 1956 to hillslopes in 1973, and the following afforestation. Changes in connectivity mainly depended on the changes in the vegetation factor and in a minor way in the total length, spatial location and type of LLE. Afforestation promoted lower and more stable connectivity at both local and catchment scales.

Coarse and fine sediment sources in nested watersheds with eucalyptus forest

“…Runoff connectivity (López‐Vicente, Nadal‐Romero, & Cammeraat, ; Zimmermann, Zimmermann, Turner, Francke, & Elsenbeer, ) possibly explains the large changes in sediment source contributions observed over very short distances between sampling site, that is, the coarse sediment being able to pass from the eucalyptus stand through the areas of riparian forest to the river, but fine sediment was not, and in some sites, sediment being able to move from the road through the eucalyptus stand to the river without any sediment being contributed from the eucalyptus stand at the same time. Zimmermann et al () found that seasonal differences in moisture strongly influence connectivity, even under light rainfall conditions but are increased rapidly as rainfall frequency raises, eventually leading to full connectivity and surface drainage of entire hillslopes.…”

Assessment of structural sediment connectivity within catchments: insights from graph theory

“…Second, this index takes into account all the links between a cell and all other components of the catchment, in agreement with the definition of connectivity. Third, the index can be mapped enabling comparisons between various locations (a specific tool has been developed in ArcGIS), and the calculation of maps of connectivity evolution over time (see, for example, case study applications in, among others, Foerster at al., 2014 andLópez-Vicente et al, 2016). Nevertheless, this index remains empirical and comparisons between catchments should be made carefully.…”

Effect of Salvage Logging and Check Dams on Simulated Hydrological Connectivity in a Burned Area

“…The ability of this index has been proved in different fields and catchments, such as in Austria (Heckmann & Schwanghart, ), France (Gay et al, ) and Japan (Chartin et al, ). In Spain, the studies of López‐Vicente et al (, ) and Foerster et al () proved their capacity to map runoff and sediment connectivity.…”