In this research paper, we analysed the behaviour of Tropical Andean glaciers in a changing climate. We used multi-source satellite images as well as meteorological datasets to achieve this objective. Representative glaciers in four different climatic zones, namely the inner tropics, northern wet outer tropics, southern wet outer tropics and dry outer tropics, were considered in this study. Changes in annual maximum snowline during 1985 -2015 and also the decadal changes in the area between 1975 and 2015 of these glaciers were calculated. Furthermore, we analysed the rate of glacier retreat during the occurrence of El Niño-Southern Oscillation and Pacific Decadal Oscillation. It is observed that the glaciers in both the inner and outer tropics underwent retreat during the study period and most of this retreat occurred during 1975 -1997 which is parallel with the so-called Pacific shift. Exceptional variations in snowline altitude were observed when an El Niño event occurs during the warm phase of the Pacific Decadal Oscillation. No significant signals of the recent hiatus in global warming were observed, except in the dry outer tropics which are situated near the subtropical region.
Este trabalho recuperou registros históricos de precipitação e eventos extremos em jornais nos primeiros 60 anos do século XX e comparou com séries de reanálises a fim de investigar quais eventos extremos históricos coincidem em data e intensidade com os extremos das reanálises, no Rio Grande do Sul (RS). A série histórica gerada foi construída a partir de notícias de inundação, enchentes, estiagens e secas nas notícias pesquisadas. As reanálises utilizadas provem da Universidade de Delaware (DLW) e consistem em uma grade de 0,5º x 0,5º disponíveis para o período 1900 - 2008. As séries anômalas foram dividas em três zonas (Campanha, Litoral e Planalto) para melhor detalhamento do comportamento espacial e analisadas nas fases: El Niño, Neutro e La Niña. Observou-se que as zonas Campanha e Planalto são mais suscetíveis às fases do El Niño – Oscilação Sule a zona Litoral demonstrou menor influência aparente. A análise das séries de anomalias DLW e de todos os aglomerados de notícias encontradas, coincidem com anomalias iguais ou superiores (inferiores) a 50 (-50 mm) mensais. Com exceção de um único evento na década de 1950 que não coincidiu com os episódios extremos de precipitação. Abril de 1959 teve a maior anomalia do período (200 mm, no valor mínimo para as três zonas) e a menor ocorreu em outubro de 1924 (-85 mm, no valor mínimo entre as três zonas). Conclui-se que esta comparação e os registros históricos possibilitaram determinar a ocorrência dos eventos extremos de precipitação e também identificar o número de dias chuvosos de cada episódio. A fase neutra demonstrou anomalias positivas (negativas) nos mesmos níveis das anomalias de El Niño e La Niña a partir de 1930, indicando que outros fatores e modos de variabilidade também devem influenciar na precipitação do RS.
This study investigated the intensity and spatial distribution of precipitation anomalies in Rio Grande do Sul state (RS) during the 20th century by analyzing the influence of El Niño – Southern Oscillation (ENSO) in its three phases. Reanalyzes from the University of Delaware (V5) were used. Precipitation anomalies were divided into three zones (Campaign, Plateau, Coast) to investigate possible differences in precipitation under ENSO influence. Alexandersson's Standard Normal Homogeneity Test was applied to verify possible structural breaks. Wavelets were used to rate the periodicity of precipitation anomalies into three phases. Anomalies that occurred in El Niño and La Niña phases were classified in contingency tables as weak, average, and strong to evaluate the qualitative behavior of these precipitation anomalies. It was found that precipitation anomalies presented a structural break in 1955 when the tendency to positive anomalies increased. From 1955, precipitation anomalies increased at least 0.5 standard deviation while the frequency of these anomalies decreased from 85 to 60 months. Peaks of positive anomalies in El Niño were higher than 200 mm. In neutral cases, anomalies intensified in 0.5 standard deviation since 1970. Negative anomalies did not show specific behavior in any ENSO phase. Contingency tables indicated that La Niña events did not present any visible influence pattern. It could intensify the episodes of positive and negative precipitation anomalies in at least 0.5 (-0.5) standard deviation. Therefore, La Niña events could increase or decrease the monthly anomaly but do not show any tendency to negative anomalies. Weak El Niños tends to contribute to negative precipitation anomalies while strong cases are associated with an average increase of 2 standard deviations in positive anomalies. It was concluded that the influence of ENSO in RS is stronger in El Niño than in La Niña. Still, both may induce negative and positive anomalies, depending on the intensity of each case. Wavelet analysis revealed that cycles that did not coincide with El Niño/La Niña showed an increase (decrease) of 0.5 (-0.5) standard deviation is positive (negative) anomalies. The increase of anomalies in neutral phases indicated that other climatic variability modes and the intensity of meteorological events decreased the 25 and 43 months cycles and increased the precipitation in RS.
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