Características das chuvas na distribuição temporal da interceptação vegetal em região semiárida

Abstract

In regions of water shortage, losses from interception and the characteristics of throughfall play an important role in the ecohydrological processes of forest soils. In this respect, the aim of the present study was to understand the processes of rainfall interception and their temporal distribution in an area of seasonally dry tropical forest in the Brazilian semi-arid region, as a function of the rainfall characteristics. The research was carried out in an experimental micro basin in the district of Iguatu, in the State of Ceará, with predominantly seasonally dry tropical forest (SDTF) vegetation - woody Caatinga, under regeneration for 39 years. From 2010 to 2016, throughfall, stemflow down tree trunks, and losses from plant interception were monitored in an area of 10 x 10 m2 , with 185 recorded events. An automatic tilting-float pluviograph was used to understand the characteristics of the external and throughfall. To investigate the temporal distribution of the throughfall, data were collected during the rainy season (January to April) of 2017, totalling 30 natural rainfall events. The rainfall characteristics were investigated using Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), defining possible similar groups relevant to interception and its determinant rainfall variables, giving rise to three different classes of rainfall events. The application of PCA formed two components, explaining 86.6% of the data, one component comprising the maximum intensities and the other rainfall duration and average intensity. Despite the mean rainfall intensity showing low correlation with all the variables, it can still be used in studying losses through plant interception, as it is simpler to determine than the maximum rainfall intensity over 30 minutes (I30). Greater losses from interception were recorded for class I rainfall, characterising events of low rainfall depth, low I30, short duration and low occurrence. There was a decrease in losses through plant interception of 17 percentage points between the first and last rainfall class, due to the increase in rainfall depth, duration and (I30). Vegetation causes a reduction in the total precipitation that effectively reaches the ground, generating an increase in rainfall duration, and lower maximum intensities, expressing the importance of the plant cover in controlling the processes of flow generation and water erosion. For each rainfall event there is a temporal delay in throughfall, so that for rainfall ≤ 0.8 mm during the first five minutes of rain, no event was able to generate throughfall, while throughfall was recorded for all events of 20 minutes’ duration. Although total precipitation is the dominant characteristic, other factors interfere in the temporal variability of throughfall, and there is a need for more detailed studies on a smaller time scale. This study showed that the rainfall characteristics investigated provide important explanations for understanding the process of loss by interception and the temporal distribution of throughfall.