Browsing by Author "Segura Cajachagua, Hans Mikhail"
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Item Restricted Contrasting North–South changes in Amazon wet-day and dry-day frequency and related atmospheric features (1981–2017)(Springer, 2019) Espinoza, Jhan Carlo; Ronchail, Josyane; Marengo, José Antonio; Segura Cajachagua, Hans MikhailThis study provides an updated analysis of the evolution of seasonal rainfall intensity in the Amazon basin, considering the 1981–2017 period and based on HOP (interpolated HYBAM observed precipitation) and CHIRPS (The Climate Hazards Group Infrared Precipitation with Stations) rainfall data sets. Dry and wet day frequencies as well as extreme percentiles are used in this analysis, producing the same results. Dry-day frequency (DDF) significantly increases in the Southern Amazon (p<0.01), particularly during September–November (SON) in the Bolivian Amazon, central Peruvian Amazon and far southern Brazilian Amazon. Consistently, total rainfall in the southern Amazon during SON also shows a significant diminution (p<0.05), estimated at 18%. The increase in SON DDF in the southern Amazon is related to a warming of the northern tropical Atlantic Ocean and a weakening of water vapour flux from the tropical Atlantic Ocean. The increase in DDF in the southern Amazon is related to enhanced wind subsidence (ascendance) over the 10°S–20°S (5°S–5°N) region and to a deficit (excess) of specific humidity at 1000–300 hPa south of 10°S (north of the 5°S), which suggest a reduction of deep convection over southern Amazonia. Subsidence over the southern Amazon shows a significant trend (p<0.01), which can explain the significant increase in DDF. Wet-day frequency (WDF) significantly increases in the northern Amazon, particularly during the March–May (MAM) period (p<0.01), producing an estimated rainfall increase during MAM of 17% (p<0.01) between 1981 and 2017. Significant changes in both WDF and rainfall in northern Amazon have been detected in 1998 (p<0.01). After 1998, the increase in MAM WDF and rainfall is explained by enhanced moisture flux from the tropical North Atlantic Ocean and an increase in deep convection over the northern and northwestern Amazon. These evolutions in DDF and WDF and in the tropical atmosphere occur simultaneously with an increase in sea surface temperature in the northern Atlantic Ocean, particularly after the mid-1990s. These results provide new insight into rainfall variability and climatic features related to increasing dry season length in southern Amazonia. Severe recent droughts may be associated with the increase in DDF in the South. In addition, the increase in MAM rainfall intensity in northern Amazon after 1998 may be associated with several historical floods that occurred after this date.Item Open Access Estudio del ciclo hidrológico de la cuenca amazónica mediante el uso de sensoramiento remoto: análisis de evapotranspiración(Universidad Nacional Agraria La Molina, 2014) Segura Cajachagua, Hans MikhailLa evapotranspiración tiene un rol relevante en el cálculo del balance hídrico: sin embargo. estudios sobre la evapotranspiración en la cuenca Amazónica (CA) son escasos. En este trabajo se analizó la evapotranspiración a escala puntual y espacial. En el primer análisis se utilizaron datos de evapotranspiración de torres de flujo (TF) del proyecto LBA. La evapotranspiración calculada con las ecuaciones de Penman-Monteith y Priestley-Taylor (usando datos meteorológicos de las TF). El producto de evapotranspiración satelital MOD 16 y el modelo GLEAM. Los resultados de este análisis mostraron que la evapotranspiración está influenciada por la radiación neta, el tipo de vegetación y el contenido de agua en el suelo. Debido a estas características MOD 16 y GLEAM no representan adecuadamente la evapotranspiración en bosques amazónicos ya que toman datos de Reanálisis como variables meteorológicas de entrada para sus algoritmos. Sin embargo la ecuación de Priestley-Taylor tiene una adecuada representación de la evapotranspiración teniendo un R2 mayor a 0.5 en estos ecosistemas. Además, la ecuación Penman-Monteith sobrestima la evapotranspiración mientras que Priestley Taylor la subestima. En el análisis espacial se calculó la evapotranspiración usando un balance de agua con los datos de precipitación (TRMM) contenido de agua en el suelo (GRACE) y caudales (ORE-HYBAM) para nueve sub-cuencas amazónicas. Los resultados mostraron que la CA tiene una evapotranspiración promedio de 3.48 mm d -1. Las sub-cuencas con mayor evapotranspiración son Xingú, Madeira Baja y Tapajós ubicadas al Sur de la CA, y las sub-cuencas con menor evapotranspiración son Marañón, Ucayali y Rio Negro (< 2 mm d-1). Los valores bajos de evapotranspiración en Marañón y Ucayali podrían estar afectados por la presencia de los Andes, los cuales incrementan la escorrentía y disminuyen la evapotranspiración. Finalmente concluimos que los datos del TRMM y GRACE son útiles para estudios en el balance hídrico en las sub-cuencas amazónicas.Item Open Access Evidencing decadal and interdecadal hydroclimatic variability over the Central Andes(IOP Publishing, 2016-09-14) Segura Cajachagua, Hans Mikhail; Espinoza, Jhan Carlo; Junquas, Clementine; Takahashi, KenIn this study we identified a significant low frequency variability (8 to 20 years) that characterizes the hydroclimatology over the Central Andes. Decadal–interdecadal variability is related to the central-western Pacific Ocean (R² = 0.50) and the zonal wind at 200 hPa above the Central Andes (R² = 0.66). These two oceanic–atmospheric variables have a dominant decadal–interdecadal variability, and there is a strong relationship between them at a low frequency time scale (R² = 0.66). During warming decades in the central-western Pacific Ocean, westerlies are intensified at 200 hPa above the Central Andes, which produce decadal periods of hydrological deficit over this region. In contrast, when the central-western Pacific Ocean is cooler than usual, easterly anomalies prevail over the Central Andes, which are associated with decades of positive hydrological anomalies over this region. Our results indicate that impacts of El Niño on hydrology over the Central Andes could be influenced by the low frequency variability documented in this study.Item Open Access Evolution of wet‐day and dry‐day frequency in the western Amazon basin: relationship with atmospheric circulation and impacts on vegetation(American Geophysical Union (AGU), 2016-11) Espinoza, Jhan Carlo; Segura Cajachagua, Hans Mikhail; Ronchail, Josyane; Drapeau, Guillaume; Gutierrez Cori, OmarThis paper documents the spatiotemporal evolution of wet‐day and dry‐day frequency (WDF and DDF) in the western Amazon, its relationships with oceanic and atmospheric variability and possible impact on vegetation. WDF and DDF changed significantly during the 1980–2009 period (p < 0.05). An increase in WDF is observed after 1995 over the northern part of the western Amazon (Marañón basin). The average annual value of WDF changed from 22 days/yr before 1995 to 34 days after that date (+55% after 1995). In contrast, DDF increased significantly over the central and southern part of this region (Ucayali basin) after 1986. Average annual DDF was 16.2 days before 1986 and 23.8 days afterward (+47% after 1986). Interannual variability in WDF appears to be modulated by changes in Pacific SST and the Walker cell during the November–March season. This mechanism enhances convective activity over the northern part of the western Amazon. The increase in DDF is related to warming of the North Tropical Atlantic SST, which produces changes in the Hadley cell and subsidence over the central and the southern western Amazon. More intense seasonal hydrological extremes in the western Amazon therefore appear to be related to changes in WDF and DDF that occurred in 1995 and 1986, respectively. During the 2001–2009 period, an index of vegetation condition (NDVI) appears negatively correlated with DDF (r = −0.95; p < 0.0001). This suggests that vegetation in the western Amazon is mainly water limited, rather than light limited and indicates that the vegetation is highly sensitive to concentration of rainfall.Item Restricted Holocene changes in monsoon precipitation in the Andes of NE Peru based on δ¹⁸O speleothem records(Elsevier, 2016-08-15) Bustamante, M. G.; Cruz, F. W.; Vuille, M.; Apaéstegui Campos, James Emiliano; Strikis, N.; Panizo, G.; Novello, F. V.; Deininger, M.; Sifeddine, A.; Cheng, H.; Moquet, J. S.; Guyot, J. L.; Santos, R. V.; Segura Cajachagua, Hans Mikhail; Edwards, R. L.Two well-dated δ¹⁸O-speleothem records from Shatuca cave, situated on the northeastern flank of the Peruvian Andes (1960 m asl) were used to reconstruct high-resolution changes in precipitation during the Holocene in the South American Summer Monsoon region (SASM). The records show that precipitation increased gradually throughout the Holocene in parallel with the austral summer insolation trend modulated by the precession cycle. Additionally the Shatuca speleothem record shows several hydroclimatic changes on both longer- and shorter-term time scales, some of which have not been described in previous paleoclimatic reconstructions from the Andean region. Such climate episodes, marked by negative excursions in the Shatuca δ¹⁸O record were logged at 9.7–9.5, 9.2, 8.4, 8.1, 5.0, 4.1, 3.5, 3.0, 2.5, 2.1 and 1.5 ka b2k, and related to abrupt multi-decadal events in the SASM. Some of these events were likely associated with changes in sea surface temperatures (SST) during Bond events in the North Atlantic region. On longer time scales, the low δ¹⁸O values reported between 5.1-5.0, 3.5–3.0 and 1.5 ka b2k were contemporaneous with periods of increased sediment influx at Lake Pallcacocha in the Andes of Ecuador, suggesting that the late Holocene intensification of the monsoon recorded at Shatuca site may also have affected high altitudes of the equatorial Andes further north. Numerous episodes of low SASM intensity (dry events) were recorded by the Shatuca record during the Holocene, in particular at 10.2, 9.8, 9.3, 6.5, 5.1, 4.9, 2.5 and 2.3 ka b2k, some of them were synchronous with dry periods in previous Andean records.Item Open Access Impacto de la resolución horizontal de un modelo regional sobre el afloramiento costero frente a Perú(Instituto Geofísico del Perú, 2014-12) Montes Torres, Ivonne; Fajardo Urbina, Jeancarlo Manuel; Ramos, Yakelyn; Saavedra Huanca, Miguel; Aparco Lara, Jonathan; Segura Cajachagua, Hans Mikhail; Hurtado, P.; Mosquera Vásquez, Kobi Alberto; Takahashi, KenEl propósito de este trabajo es estudiar y entender la dinámica del afloramiento costero bajo condiciones promedio usando del modelo numérico de alta resolución ROMS. Dicho modelo es configurado usando dos diferentes resoluciones espaciales (i.e., dos tamaños de grilla diferentes) y aplicando las mismas condiciones iniciales y de frontera a fin de entender las consideraciones dinámicas que se deben tomar en cuenta para modelar la dinámica del afloramiento costero durante las diferentes fases de El Niño – Oscilación del Sur (ENSO).Item Restricted Intra-seasonal rainfall variability in the Amazon basin related to large-scale circulation patterns: a focus on western Amazon–Andes transition region(Royal Meteorological Society, 2018-04) Paccini Peña, Laura Giulianna; Espinoza, Jhan Carlo; Ronchail, Josyane; Segura Cajachagua, Hans MikhailThis study aims to relate the intra‐seasonal rainfall variability over the Amazon basin to atmospheric circulation patterns (CPs), with particular attention to extreme rainfall events in the Amazon–Andes region. The CPs summarize the intra‐seasonal variability of atmospheric circulation and are defined using daily low‐level winds from the ERA‐Interim (1.5° × 1.5°) reanalysis for the 1979–2014 period. Furthermore, observational data of precipitation and high‐resolution TRMM 3B42 (∼25 km), 2A25 PR (∼5 km) and CHIRPS (∼5 km) data products are related to the CPs throughout the Amazon basin. Nine CPs are determined using a hybrid method that combines a neural network technique (self‐organizing maps, SOM) and hierarchical ascendant classification. The CPs are characterized by a specific cycle with alternative transitions and a duration of 14 days on average. This configuration initially results in northerly winds to southerly winds towards the northern or eastern Amazon basin. The related rainfall suggests that it is driven mainly by CP dynamics. In addition, we demonstrate a good agreement amongst the four rainfall data sets: observed precipitation, TRMM 3B42, TRMM 2A25 PR and CHIRPS. Furthermore, special attention is given to the Amazon–Andes transition region. Over this region, two particular CPs (CP4 and CP5) are identified as the key contributors of maximum and minimum daily rainfall, respectively. Thus, during the dry season, 40.8% (11.4%) of the CP5 (CP4) days demonstrate rainfall of less than 1 mm day⁻¹, while during the wet season, 6.2% (14.6%) of the CP5 (CP4) days show rainfall amounts higher than the seasonal 90th percentile (10.4 mm day⁻¹). This study provides additional information concerning the intra‐seasonal circulation variability in Amazonia and demonstrates the value of using remote sensing precipitation data in this region as a tool for forecast in areas lacking observable information.