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Item type:Publication, Regionalization of Rainfall in the Upper Madeira Basin Based on Interannual and Decadal Variability: A Multi-Seasonal Approach(John Wiley and Sons Ltd, 2023-11-30)Identifying rainfall regions associated with specific modes of variability is of practical interest for water resources management, seasonal forecasting, and mitigation of weather-related risks. This study aims to identify homogeneous rainfall regions within the ~1 million km2 Upper Madeira River basin—southwestern Amazon—by their interannual and decadal variability and relates this variability to ocean indices. An observed dataset of 146 ground-based rainfall stations, distributed throughout the Andes and the Amazon, and homogenized at the monthly time-step for the period 1980–2016, was used for the analysis. With no spatial constraints, hierarchical cluster analysis and principal component analysis (PCA) optimally grouped stations into 10 rainfall homogenous regions. The value of the regionalization for interpreting the rainfall variability was evaluated by relating the seasonal rainfall time series of the regions with ocean indices. Then, by applying PCA to seasonal rainfall series and linking the principal components to sea surface temperature and ocean indices, an insight into the main large-scale drivers of the rainfall spatio-temporal variability in this basin at interannual and decadal scales is provided. This analysis identified differences in the year-round influences of the tropical Pacific and/or Atlantic oceans on the 10 homogenous regions. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Recent changes in the dry-to-wet transition season in the Andean Altiplano and related atmospheric circulation patterns (1981–2022)(Springer Science+Business Media, 2025-01-01)Drought-related impacts in the southern Tropical Andes are crucial for economic activities. Here, precipitation decreases (p < 0.1) during the dry-to-wet transition season (SON) based on CHIRPS (1981–2023) and meteorological stations (1973–2016). In addition, a decline in specific humidity and moisture flux is detected (1979–2022). The precipitation trend is stronger (p < 0.05) in the southern Titicaca, Desaguadero, Poopó and Coipasa Salt Pan hydrological system (TDPS) and extends southwards (20°S-30°S). A delayed onset and a reduced duration of the wet season are observed in the TDPS (p < 0.05), although precipitation intensifies during DJF in the southwestern TDPS (p < 0.05).To analyze the atmospheric features related to these changes, we derive atmospherics circulation patterns (CPs) from standardized anomalies of daily 200-hPa winds (1979–2022) using a weather classification technique. We identify 9 CPs, characterized by four ‘‘dry’’ (D1, D2, D3, and D4), three ‘‘wet’’ (W1, W2 and W3), and two ‘‘transitional’’ patterns (T1 and T2). During SON, the frequency of the W1 (D3) is negatively (positively) correlated with the onset date of the wet season (p < 0.05). Through the period 1979–2022, the frequencies of the D3 and the predominantly dry T1 increase (p < 0.1 and p < 0.05, respectively). Conversely, W1 frequency diminishes substantially since 2010. The physical mechanisms associated are discussed. In conclusion, increased D3 and T1 frequencies, and decreased W1 are related to the diminution of precipitation during SON and to the shortening of the wet season length. We also show that the extreme drought of 2022 was characterized by an unprecedented frequency of dry CPs, particularly during November.2