From 18 to 27 March 2015, northern, central, and southern Chile experienced a series of extreme hydrometeorological events. First, the highest surface air temperature ever recorded in Santiago (with reliable records dating to 1877), 36.8°C at Quinta Normal, was measured at 15:47 local time on 20 March 2015. Immediately following this high heat event, an extreme precipitation event, with damaging streamflows from precipitation totals greater than 45 mm, occurred in the semiarid and hyperarid Atacama regions. Finally, concurrent with the heavy precipitation event, extremely warm temperatures were recorded throughout southern Chile. These events were examined from a synoptic perspective with the goal of identifying forcing mechanisms and potential interaction between each analysis which provides operational context by which to identify and predict similar events in the future. Primary findings were as follows: (1) record warm temperatures in central Chile resulted from anomalous lower troposphere ridging and easterly downslope flow, both of which developed in response to an anomalous midtroposphere ridge‐trough pattern; (2) a cutoff low with anomalous heights near one standard deviation below normal slowly moved east and was steered ashore near 25°S by circulation around a very strong ridge (anomalies more than 3 standard deviations above normal) centered near 60°S; (3) anomalously high precipitable water content (20 mm above climatological norms) over the Peruvian Bight region was advected southward and eastward ahead of the cutoff low by low‐level northwesterly flow, greatly enhancing observed precipitation over northern Chile.

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Este trabalho objetivou avaliar a influência da antropização e de secas severas na dinâmica da cobertura florestal de um fragmento de caatinga na região semiárida do Brasil, ao longo de 32 anos. Para o cálculo do índice de seca, agrupou-se os valores de precipitação média pondera           da anual da série histórica (1988 - 2019) em Decis. A partir do quantitativo de área encontrada nas classes de uso e ocupação (cobertura florestal conservada, cobertura natural campestre, área antropizada e corpos d’água) dos anos extremos secos e chuvosos, procedeu-se à análise estatística multivariada pelo método da análise de agrupamento hierárquico. Os valores médios dos agrupamentos foram submetidos à análise estatística e confrontados pelo teste T de Student (p ≤ 0,05). Foram encontrados três grupos distintos: G1 constituído por anos secos e muito secos da década de 90, o agrupamento 2 formado por anos extremos úmidos e muito úmidos, independentemente do período, e G3 (agrupamento intermediário) constituído tanto por anos típicos secos quanto chuvosos, especificamente de períodos mais recentes (2000 a 2019). Os grupos G2 e G3 contribuíram com as maiores quantitativo de cobertura florestal conservada, 143.176,50 e 144.928,13 ha, respectivamente. Os resultados demonstram que a precipitação pluviométrica está mais estritamente correlacionada com as áreas antropizadas do que propriamente com a regeneração natural da cobertura florestal. A vegetação arbórea-arbustiva do fragmento investigado tem passado por um processo de regeneração natural na década recente (2002 - 2019) em virtude do abandono de áreas anteriormente antropizadas na década de 90. Drought and Anthropogenic Effect on the Dynamics of Forest Cover in a Fragment of Caatinga Phytogeographic Domain A B S T R A C TThe aim of this study was to evaluate the influence of anthropogenic action and severe drought on the dynamics of forest cover in a fragment of caatinga in the semi-arid region of Brazil, over 32 years. To calculate the drought index, the values for weighted mean annual precipitation from an historical series (1988 - 2019) were grouped into deciles. Based on the quantification of the area found in the classes of use and occupation (conserved forest cover, natural rural cover, anthropogenic area and water bodies) for the extreme dry and rainy years, multivariate statistical analysis was carried out using hierarchical cluster analysis. The mean values of the clusters were submitted to statistical analysis and compared by Student's t-test (p ≤ 0.05). Three distinct groups were found: G1, consisting of dry and very dry years from the 1990s; G2, formed by extreme wet and very wet years regardless of the period; and G3 (intermediate group), comprising both dry and rainy years, specifically from more recent periods (2000 to 2019). Groups G2 and G3 contributed the greatest amount of conserved forest cover, 143,176.50 and 144,928.13 ha respectively. The results show that rainfall is more closely correlated with the anthropogenic areas than with the natural regeneration of forest cover. The woody vegetation of the fragment under investigation has undergone a process of natural regeneration during the last decade (2008 - 2016), due to previously anthropogenic areas being abandoned in the 1990s.Keywords: Caatinga, remote sensing, desertification.