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Instituto Politecnico de Bragança (2019)

Caracterização e efeitos dos períodos de seca e da aridez na suscetibilidade do solo à erosão hídrica no nordeste de Portugal

Royer, Ana Caroline

Titre : Caracterização e efeitos dos períodos de seca e da aridez na suscetibilidade do solo à erosão hídrica no nordeste de Portugal

Auteur : Royer, Ana Caroline

Université de soutenance : Instituto Politecnico de Bragança

Grade : Mestre em Tecnologia Ambiental 2019

The global climate framework has seen clear changes over recent years and future forecasts continue to alert to changing scenarios. One of the persistent elements in the scenarios designed for this context is the increase in the variability of weather conditions with prolonged periods of drought and, in opposition, the occurrence of extremes accused of precipitation, generators of erosive processes. This could severely affect the driest areas, as is the case for much of Portugal’s internal NE, which has erosion as a present threat. The effects of prolonged periods of drought on the erosive response to the first rains that follow are not yet well described and understood. Faced with this problem, the development of this work involved the characterization of periods of drought and dryness, as well as its relation to soil degradation, especially water erosion. For this, the climatic classifications of the Soil Chart and the Aridity Index (NE) for NE of Portugal were compared and an analysis of trends of erosivity and extreme events was performed using SPI (Standardized Precipitation Index), AI and climatological normals, based on data meteorological and mapped material. The evaluation of soil erosive response to the first precipitations after a prolonged drying period was performed by means of a rainfall simulator, with two raining of 30 min each with interval of 1 h between the simulations applied to the 5 Soil Units representative of NE. With the premise that erosion reduces soil thickness and, as a consequence, storage capacity, a statistical regression study of soil moisture (SM) was also performed, originating from satellite sensors, and the water balance storage variable (A) obtained from terrestrial data from meteorological stations. The climate classifications are consistent and converge, with hot and semi-arid lands being more influenced by the rainfall regime. The analysis of precipitation trends shows a reduction in the average along the evolution in the time, and is coincident for the situation of increase of the erosivity of the precipitations in the arid zones. SPI and AI indicate a greater frequency and pronouncement of extreme events, with increased aridity conditions. The rainfall simulations showed that the initial moisture content of the soil when submitted to the first precipitations is a condition of soil and water losses due to water erosion. It was found that the effect of the first precipitations is not necessarily reflected in greater soil losses by runnof, but in a higher sediment concentration and splash losses. The relation between SM and A is verified, with r² ranging from 0.69 to 0.94, with the logistic model and the condition of Amáx = 50 mm tending to be better among the scenarios tested. The constraint found was the increase of the standard error of the estimation according to the increase of Amáx, behaviour that may be object of future efforts. The ability of remote data to represent the drying and wetting phenomena by the hysteresis model reveals the sensitivity and potential of the SM data as a tool for forecasting and monitoring.

Mots clés  : Degradação do solo Índice de aridez Balanço hídrico Humidade do solo ESA CCI Simulação de chuva SPI


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