Hydrological behaviour of vertisols in the Brazilian semi-arid region: the importance of rainfall of less than 30 mm

Eunice Maia De Andrade ,Rafael Do Nascimento Rodrigues ,Helba Araújo De Queiroz Palácio ,José Bandeira Brasil ,Maria João Guerreiro

doi:10.5935/1806-6690.20200029

Abstract

The greater probability of small rainfall events occurring in semi-arid regions, and the little understanding of their role in hydrological processes, has led to this investigation of surface runoff generated during these events in two adjacent micro basins in the Brazilian semi-arid region. The types of plant cover to be investigated were the Phytogeographical Caatinga Domain under regeneration for 35 years (CPDReg) and thinned CPD (CPDThin), which consisted of the elimination of trees with a diameter of <10 cm. Two historical series were considered, one of 40 years (1974-2013) with 2,259 events and the other consisting of 247 rainfall events of <30 mm from 2009 to 2013. The cumulative frequency distribution showed that the series of 247 24-hour events proved to be statistically representative in investigating hydrological processes in the Brazilian semi-arid region, compared to the long series of 2,259 events. Irrespective of the pattern, rainfall with an intensity of less than 17 mm h-1 generated effective precipitation with small depths (<2 mm). Regardless of the rainfall pattern, the lowest effective precipitation was registered for the plant cover of thinned CPD, both on an annual scale and per event. The occurrence of 3 or 4 consecutive dry days is enough for events of <30 mm to generate no runoff, due to the appearance of micro-cracks formed in vertisols during the drying process. It is believed, therefore, that the expansion and contraction of vertic soils is the main determinant for the start of Pe in areas with a water source (micro basins of <2 ha) in the CPD.

Highlights

Feeding costs are still an obstacle to several small ruminant farming systems, especially when concentrate diets are used in periods of forage deficit, which despite the good nutritional value, make the system more expensive
Its main economic use is by cutting the leaves for wax production, besides that fruits are used for animal feeding in extensive systems in the areas of occurrence of the plants, which should occur soon after ripening, due to the rapid decomposition of the pericarp after the fruit falls on the ground
The inclusion of fruit of the carnauba and tucum palm trees in the diets resulted in a reduction (P

Summary

Introduction

Feeding costs are still an obstacle to several small ruminant farming systems, especially when concentrate diets are used in periods of forage deficit, which despite the good nutritional value, make the system more expensive. In this sense, it is sought to know better the alternative ingredients for diets, mainly due to the high production of some native plant species in the dry period. Among the native species to the Mid-North subregion, stand out carnauba Copernicia prunifera (Mill.) H.E. Moore) and tucum (Bactris setosa Mart.) palm trees, whose fruits are commonly consumed by herds of small ruminants in an area of natural occurrence of these palms, with empirical reports of good acceptance and contribution to maintaining the weight of the animals. Its main economic use is by cutting the leaves for wax production, besides that fruits are used for animal feeding in extensive systems in the areas of occurrence of the plants, which should occur soon after ripening, due to the rapid decomposition of the pericarp after the fruit falls on the ground

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