Effect of dry spells and soil cracking on runoff generation in a semiarid micro watershed under land use change

• Published in: Journal of hydrology (Amsterdam) Vol. 541; pp. 1057 - 1066
• Main Authors: dos Santos, Julio Cesar Neves, de Andrade, Eunice Maia, Guerreiro, Maria João Simas, Medeiros, Pedro Henrique Augusto, de Queiroz Palácio, Helba Araújo, de Araújo Neto, José Ribeiro
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.10.2016
• Subjects: Andropogon gayanus; Antecedent soil moisture content; Brazil; cracking; data collection; Dry spells; grasses; humidity; indigenous species; Land use; land use change; monitoring; planning; preferential flow; rain; runoff; Runoff processes; Semiarid; slash; soil water; soil water content; tropical forests; tropics; vegetation cover; Vertisols; water resources; watersheds; Brazil; Runoff processes; Dry spells; Antecedent soil moisture content; Semiarid; Land use
• DOI: 10.1016/j.jhydrol.2016.08.016
• ISSN: 0022-1694

•Dry spells and formation of soil cracks were determinant for flow generation.•The cracks formed in the Vertisol created preferential infiltration paths.•Temporal distribution of rainfall was an underlying factor for runoff generation.•Rainfall events occurring after dry spells lead to little increments of runoff.•Vegetation plays a secondary role on flow initiation on expansive clay soils. Soil and water resources effective management and planning in a river basin rely on understanding of runoff generation processes, yield, and their relations to rainfall. This study analyzes the effects of antecedent soil moisture in an expansive soil and the influence of dry spells on soil cracking, runoff generation and yield in a semiarid tropical region in Brazil subject to land use change. Data were collected from 2009 to 2013 in a 2.8ha watershed, totaling 179 natural rainfall events. In the first year of study (2009), the watershed maintained a typical dry tropical forest cover (arboreal-shrub Caatinga cover). Before the beginning of the second year of study, gamba grass (Andropogon gayanus Kunth) was cultivated after slash and burn of native vegetation. Gamba grass land use was maintained for the rest of the monitoring period. The occurrence of dry spells and the formation of cracks in the Vertisol soil were the most important factors controlling flow generation. Dry spells promoted crack formation in the expansive soil, which acted as preferential flow paths leading to high initial abstractions: average conditions for runoff to be generated included soil moisture content above 20%, rainfall above 70mm, I30max above 60mmh−1 and five continuous dry days at the most. The change of vegetation cover in the second year of study did not alter significantly the overall conditions for runoff initiation, showing similar cumulative flow vs. rainfall response, implying that soil conditions, such as humidity and cracks, best explain the flow generation process on the semiarid micro-scale watershed with Vertisol soil.