Mapping headwater systems using a HS-GIS model. An application to landscape structure and land use planning in Portugal

•The Headwater System is an important area of the drainage basin.•The threshold of 0.1km2 of drainage area is a good approximation to channel head identification.•The headwater system must be part of land use planning policies.•The type of land use in HS areas will determine the dynamic stability of the drainage basin. The Headwater System (HS) is defined as the area between the ridge line, and the beginning of the channel network. The HS have high importance in the hydrological, geomorphological, and biological processes of the drainage basin. It is crucial to map HS areas in order to define the suitable land uses in the landscape related policies. The identification of the channel network beginning is particularly difficult as well as its mapping at a landscape scale. The field identification is costly in time and labor, being more operative to use models and mathematical thresholds to identify the drainage area thresholds that defines the beginning of the channel network. The aim of this work was to contribute to headwaters system mapping with the construction of a Geographic Information System model, using as channel network beginning, the thresholds of 0.1km2 drainage area. This threshold was compared and validated with 92 channel heads occurring in Portugal. The model was created in GIS allowing to define the headwater system, in order to be included in landscape plans and in green infrastructure delimitation. It was applied in Portugal and compared with data from National Ecological Reserve (REN) in Alentejo Region. It was concluded that the proposed model is a useful tool to define headwater systems with precise criteria, bridging the gaps of the existent mapping policies from REN policy. The current evaluation of land use and land cover in the HS from Portugal showed a high percentage of eucalyptus and maritime pine, which are not the best land use for these areas.