Detection of climate change and climate variability signals in Colombia and the Amazon River basin through empirical mode decomposition.
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SummarySe identifican los principales modos de variabilidad hidro-climática en series de precipitación, caudales y temperatura en Colombia y en la cuenca Amazónica, de varias resoluciones temporales, comparando los resultados obtenidos mediante las transformadas de Fourier, Onditas y Hilbert-Huang, así como identificando señales de cambio climático y variabilidad hidro-climática de largo plazo a través de la metodología de la Descomposición en Modos Empíricos.
AbstractThe hydro-climatology of Colombia exhibits significant signatures of climatic change and also strong natural climate variability at a broad range of time scales from interdecadal and interannual all the way through intradiurnal. Signals of long-term trends and of natural climate variability are detected in Colombia and the Amazon River basin using long series of monthly rainfall (100 stations), average river discharges (42 stations) and mean and minimum temperature records (37 stations) in Colombia. In the Amazon basin 29 monthly rainfall stations were studied. Stations with more than 25 years of data and well spatially distributed across Colombia and the Amazon were selected. Also, time series of average monthly river discharges were selected on 10 Colombian river basins with gauging stations along their path. For estimation, the Empirical Mode Decomposition (EMD), is used as a filtering process whereby a time series is decomposed into a finite number of intrinsic mode functions (IMFs), assuming that at any given time, many simple oscillatory modes of different frequencies coexist in a time series, where the residual represents the general trend of the series over time. The statistical significance of the trend in the EMD residuals are tested through the Mann-Kendall test for autocorrelated series and the magnitude of the trends are quantified by the Sen test. Results show that most monthly river discharges series exhibit decreasing trends, whereas the minimum temperature series show increasing trends. Results on precipitation are inconclusive as monthly records exhibit a mixed pattern of increasing and decreasing trends. However, it was established that the maximum trend magnitudes in rainfall series are located in the Colombian Pacific region (increasing trends), whereas towards the rest of the country no clear spatial pattern could be recognized. Also a consistent result between trends in rainfall and discharges in the Pacific region was found. These series exhibit increasing trends coinciding with a rising trend estimated in the Choco Low level Jet series which represents moisture advection into this particular area. In the Amazon basin the maximum trend magnitudes were found in the basin's central and south-eastern region. (Tomado de la fuente)
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