Erosion at hillslope and micro‐basin scales in the Gilbués desertification region, Northeastern Brazil

Abstract

With an area of 6,200 km2, the Gilbués badlands region in the Brazilian drylands is the largest desertification site in the Country. It is located upstream the Boa Esperança Hydroelectric Power Plant and is contiguous to an important Brazilian agricultural area. However, primary quantitative data on erosive processes are scarce or nonexistent. We analyzed on‐site data (2018–2019) concerning small‐scale (hillslope and micro basin) processes: inter‐rill gross erosion, vegetation coverage factor, sediment yield, and sediment delivery ratio. We measured gross erosion in four hillslopes using metal pins; rainfall erosivity using an automatic meteorological station; soil erodibility; and siltation of five check‐dams that control micro basins (101–103 m2) by means of an unmanned aerial vehicle. Gross erosion (102 Mg ha−1 yr−1; 7.5 mm yr−1) is up to 100‐fold the regional mean value and up to 45‐times the tolerable soil‐loss reference value (0.17 mm yr−1), showing that degradation still evolves. Sparse small vegetation directly exposes two thirds of the soil, with a high vegetation factor (0.90). The sediment delivery ratio of the micro basins is 0.88, compatible with low (12%) sediment‐deposition pattern at this scale. The Maner delivery‐ratio model mimicked field observation, which indicates that relief is the key element influencing sediment deposition there. The check‐dam effectiveness considerably decreased after the first decade of operation due to high siltation rates. Although the Gilbués badland occupies only 5% of the basin upstream of the power plant, it contributes 32% of the sediment load to reservoir and dam. This shows the relevance of the badland restoration for the regional sustainability of water and energy supply.

Maximum Entropy Distribution of Rainfall Intensity and Duration – MEDRID: a method for precipitation temporal downscaling for sediment delivery assessment

“…The efficiency of the model for total siltation rate is 0.96 (Table 6), its classification ranges from very good (Moriasi et al, 2007) to good (Ritter and Muñoz-Carpena, 2013). It supports the argument that stationary parameters such as relief (in our temporal analysis scale) play a relevant role for sediment delivery mechanisms (Simplício et al, 2020); they, therefore, increase the performance of the model over time.…”

“…Gaiser et al (2003) found that, for the Brazilian northeast region, the most fit among those equations is the one by Maner Maner (1958, hereafter Equation 10). Simplício et al (2020) had the same result for the dry Cerrado region of Gilbués (Fig. 2).…”

“…The stations in Gilbués, Aiuaba and Sumé (Fig. 2) were maintained by research groups (Simplício et al, 2020;de Figueiredo et al, 2016;Srinivasan and Galvão, 2003) and only the station of Sobral is maintained by the Brazilian Water Management Agency (ANA). Those four stations presented consistent measurements over at the least two years without gaps.…”

“…For each catchment we obtained the time series of daily rainfall from FUNCEME (2019). Sub-daily measurements are scarce and available for the whole study period only in one station in Gilbués (Simplício et al, 2020). and one in Aiuaba (de Figueiredo et al, 2016), the basins with the shortest and most recent time series.…”

“…The USLE does not directly address gully erosion (Wischmeier and Smith, 1978). Nevertheless, gullies may be major sediment sources (Bennett and Wells, 2019), especially in degraded areas such as Sumé 4 and Gilbués (Srinivasan and Galvão, 2003;Simplício et al, 2020).…”