Interceptação da chuva e escoamento superficial de água no solo no semiárido pernambucano

Abstract

The removal of vegetation allied to climatic changes alter the balance between rainfall, evapotranspiration and surface runoff of water in the soil. The understanding of the interactions between hydrology and land use change is essential for understanding hydrological functioning and climate trends. The objective of this study was to analyze the interception of rainfall in two caatinga fragments through mathematical modeling and remote sensing techniques and to evaluate the runoff of water in the soil by the runoff curve number (CN) in areas of caatinga and pasture in the semi-arid region of Pernambuco. The work was carried out in a degraded pasture (PD) and three areas of caatinga, one preserved (CP), another with predominance of angico (CA) and a third in regeneration (CR), located in the municipality of Serra Talhada - PE. Interception of rainfall (I) was evaluated only in the areas of CP and CA. Rainfall data (Pext) were obtained with a pluviometer pleaced above the canopy vegetation, while the throughfall data (Pint) were manually collected with pluviometers pleaced below the canopy vegetation. Rainfall interception data (I), defined by the difference between P and Pint, were fit to the data from exponential equation (P versus I) whose parameters describe the maximum storage capacity of the canopy (Smax) and the canopy openness (k). Four experimental sites were installed for soil water runoff (ES) measurements in each of the four areas (PD, CP, CA and CR). For this, a standard plot (1.02 m2) was used, surrounded by galvanized sheet, interconnected to a channel that led to the water drained to the collecting tanks. It applied the method curve number of Soil Conservation Service (CN-SCS) to obtain the value of the maximum infiltration capacity (S), fitting the observed data (Pext versus ES) in the four experimental areas and imposing the coefficients of (𝜆) equal to 0.1 and 0.2. Parallel to obtain CN were adjusted linear regressions between ES and Pext to compare the performance with the method curve number. To evaluate the performance, were used the mean square error (EQM), the Nash-Sutcliffe efficiency coefficient (CNS) and the coefficient of determination (R2). The interception corresponded to 33.6 and 40% of total rainfall, in both areas, CP and CA, respectively. The observed data were well adjusted to the proposed model and the correlation between Smax and N' (NDVI mean + NDVI maximum / 2) obtained in each plot allowed spatialisation in both tropical dry forests fragments. The CN values obtained with λ = 0.1 estimated the runoff better than those obtained with λ = 0.2. As the CN values generated in this work approximated those of the Soil Conservation Service (SCS) for similar conditions of use and land cover, they can be used to estimate the ES of areas that present the same conditions reported in this study.