Wetland classification of sedimentary plateu on tropical drylands - Brazilian Northeast

Tropical drylands show diverse environmental characteristics worldwide, where the high evapotranspiration rates control the water deficit. In this context, water retention areas such as wetlands are hydro-geomorphological elements essential to ecological and social sustainability. The wetland classification on dryland areas allows better management of these socio-ecological hotspots. This research identifies and classifies wetland areas on the Chapada do Araripe and its surroundings in the centre of Brazilian tropical drylands. The geomorphological unit has 6,000 km², altitudes from 500m to 1100m, and comprises limestones on the base and sandstones on the top layer. The Wetlands were identified by remote sensing and fieldwork analysis and characterized by 13 geoindicators elements (e.g., near-surface lithology, flat valley bottom, spring presence, perennial surface water, hydromorphic soils, TWI, curvature, slope). Geomorphological and hydrological conditional factors define the wetland classification. The eleven wetlands identified are distributed on narrow valleys with slopes under 0.2m/m. The rainfall accumulation patterns directly link the surface flow temporality; only two areas show perennial surface flow. The perennial/intermittent hydrological regime seems to be directly linked to land use intensity. The intense deforestation is linked to the agricultural potentiality due to higher water disponibility. Valley bottom morphology was one of the critical elements to wetland classification, and curvature and slope values characterized it. Also, as a hydro-geomorphological feature, vertical incision and incised channels define the flow concentration/diffusion grade. The plan wetlands were defined by curvature values between 0.03-0.07 and slope values under 0.08m/m. Concave wetland show curvature from 0.1 to 0.19 and slope values between 0,08-0.2m/m. Considering these parameters, four classes were delineated for Wetlands in Chapada do Araripe: (1) flat with channelled valley floor;  (2) flat with unchanneled valley bottoms;   (3) Concave with channelled valley floor; and  (4) concave with unchanneled valley bottoms. Vegetated wetlands show the predominance of vertical incision processes and the presence of continuous channels (types 1 and 3). In contrast, deforested wetlands are controlled by valley floor sedimentation/silting process and absence/discontinuity of vertical incision. The vegetation presence was more significant than the curvature characteristics of valley floor vertical incisions. The association of vegetation presence with near surface low-permeable limestone layer controlled perennial hydrological regime. In this sense, it can be concluded that the geomorphological and hydrological parameters are essential for the characterization and classification of Wetlands. Becoming critical to elaborate specific legislation that aims to protect these environments, especially those found in dry lands.