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Item type:Publication, Seasonal types in homogeneous rainfall regions of the Amazon basin(John Wiley and Sons Ltd, 2024-03-30)Due to its size and geographical features, different average annual rainfall regimes co-exist in the Amazon basin, with distinct year-to-year variability dependent on regions within the basin. In this study, we define and explain the seasonal regional types of annual regimes, that is, years with similar seasonal anomalies. Our work is based on a 205 rain gauge network distributed over five Amazonian countries, spanning a period over 30 years. Using a spectral clustering method, we identified seven sub-regions within the basin in which annual rainfall regimes are spatially homogenous. For each sub-domain, we estimated specific parameters that characterize the rainy season (onset and demise dates, sign and duration of rainfall anomalies). Finally, using spectral analysis we identified between two and four ‘seasonal type’ of precipitation in these seven sub-domains. Most of these seasonal types are in phase with the large-scale atmospheric circulation, which explains the temporal link with rainfall anomalies. The seasonal types result of the superposition of inter-annual and intra-seasonal variability whose factors are then difficult to identify and attribute. Part of the rainfall anomalies characterizing seasonal types is related to the inter-annual variability of the sea surface temperature in the Atlantic or the Pacific oceans, especially in the northeast and southeast part of the Amazon basin, whereas in other parts, strong intra-seasonal and local factors have a larger impact. The same sign and duration of anomalies do not concomitantly affect the various regions of the Amazon basin, confirming that one mode of variability does not homogeneously affect precipitation in different parts of the basin. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, The new record of drought and warmth in the Amazon in 2023 related to regional and global climatic features(Nature Research, 2024-12-01)In 2023 Amazonia experienced both historical drought and warm conditions. On October 26th 2023 the water levels at the port of Manaus reached its lowest record since 1902 (12.70 m). In this region, October monthly maximum and minimum temperature anomalies also surpassed previous record values registered in 2015 (+ 3 °C above the normal considering the 1981–2020 average). Here we show that this historical dry and warm situation in Amazonia is associated with two main atmospheric mechanisms: (i) the November 2022–February 2023 southern anomaly of vertical integrated moisture flux (VIMF), related to VIMF divergence and extreme rainfall deficit over southwestern Amazonia, and (ii) the June–August 2023 downward motion over northern Amazonia related to extreme rainfall deficit and warm conditions over this region. Anomalies of both atmospheric mechanisms reached record values during this event. The first mechanism is significantly correlated to negative sea surface temperature (SST) anomalies in the equatorial Pacific (November–February La Niña events). The second mechanism is significantly correlated to positive SST anomalies in the equatorial Pacific, related to the impacts of June–September El Niño on the Walker Circulation. While previous extreme droughts were linked to El Niño (warmer North Tropical Atlantic SST) during the austral summer (winter and spring), the transition from La Niña 2022–23 to El Niño 2023 appears to be a key climatic driver in this record-breaking dry and warm situation, combined to a widespread anomalous warming over the worldwide ocean. - Some of the metrics are blocked by yourconsent settings
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