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Seasonality of Rainfall in Colombia

DOI:10.1029/2018WR023316
Authors:
Viviana Urrea at National University of Colombia
Viviana Urrea
Andres Ochoa at National University of Colombia
Andres Ochoa
Oscar Mesa at National University of Colombia
Oscar Mesa
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Abstract and Figures

The knowledge of the annual cycle of rainfall is of primary concern for many socio‐economic activities such as agricultural planning, electricity generation, and flood and other disaster management. The annual cycle of rainfall in Colombia has been studied so far using monthly or quarterly information, identifying zones with the unimodal regime (one wet and one dry season) over the Caribbean, the Amazon and the Pacific regions and zones with the bimodal regime (two wet and two dry seasons) in the Andes. This paper explores the annual rainfall cycle in Colombia on a daily basis using historical records of 1706 rain gauges and the Climate Hazards Group Infrared Precipitation with Station data (CHIRPS) precipitation dataset. We found four types of annual precipitation regimes: unimodal, bimodal, mixed and aseasonal. The unimodal regime predominates in the low‐altitude zones of the east and the north, the bimodal and mixed regimes over the Andes mountain range and the aseasonal in the Pacific region. These results improve the statistical diagnosis of the spatial variability of the rainfall seasonality in Colombia. This phenomenon, however, is still far from being fully understood in its hydro‐climatic context. The annual migration of the Inter‐tropical Convergence Zone is not enough to explain the diversity of rainfall regimes in Colombia. Local factors such as topography and land cover could play an important role in the occurrence and duration of rainfall seasons. Map: https://www.google.com/maps/d/edit?mid=1DHhVehJh2P-9TNT8HfxCsipw7GXtfbR7&ll=4.546241553518012%2C-74.60000000000001&z=5
The five natural regions of Colombia (Instituto Geográfico Agustín Codazzi, 1997) and the Instituto de Hidrología, Meteorología y Estudios Ambientales rain gauge network. The bottom left graph shows the vertical distribution of the rain stations.
The five natural regions of Colombia (Instituto Geográfico Agustín Codazzi, 1997) and the Instituto de Hidrología, Meteorología y Estudios Ambientales rain gauge network. The bottom left graph shows the vertical distribution of the rain stations.
… 
(left) Accuracy of the Fourier classification method as a function of the FVE threshold. The visual classification was taken as a reference to determine the optimal threshold value. (middle) Regions in the dispersion diagram of FVE explained by the annual versus semiannual components. Each one of the four regions corresponds to a different seasonal regime of precipitation. (right) Box plot of FVE for the annual (gray) and semiannual (black) components of the long‐term annual cycle of the IDEAM data set for the five natural regions of Colombia (Instituto Geográfico Agustín Codazzi, 1997). FVE = fraction of the variance explained.
(left) Accuracy of the Fourier classification method as a function of the FVE threshold. The visual classification was taken as a reference to determine the optimal threshold value. (middle) Regions in the dispersion diagram of FVE explained by the annual versus semiannual components. Each one of the four regions corresponds to a different seasonal regime of precipitation. (right) Box plot of FVE for the annual (gray) and semiannual (black) components of the long‐term annual cycle of the IDEAM data set for the five natural regions of Colombia (Instituto Geográfico Agustín Codazzi, 1997). FVE = fraction of the variance explained.
… 
Examples of the rainfall regimes occurring in Colombia. Uniban gauge: mixed regime, La Raya gauge, and Aeropuerto. Vásquez Cobo gauge: unimodal regime. Observatorio Meteorológico Nacional gauge: bimodal regime. Bebedó gauge: aseasonal regime. For each gauge, the inset shows long‐term annual average cycle (black irregular line), annual and semiannual components (gray dashed lines), the resultant of both smooth black line and the gray‐shaded rectangles, and the results of the mass curve slope identification of each season average daily rainfall. In the legend the phase (ϕ), amplitude (A), and the fraction of the variance explained (FVE) for both the annual and semiannual components are also included.
Examples of the rainfall regimes occurring in Colombia. Uniban gauge: mixed regime, La Raya gauge, and Aeropuerto. Vásquez Cobo gauge: unimodal regime. Observatorio Meteorológico Nacional gauge: bimodal regime. Bebedó gauge: aseasonal regime. For each gauge, the inset shows long‐term annual average cycle (black irregular line), annual and semiannual components (gray dashed lines), the resultant of both smooth black line and the gray‐shaded rectangles, and the results of the mass curve slope identification of each season average daily rainfall. In the legend the phase (ϕ), amplitude (A), and the fraction of the variance explained (FVE) for both the annual and semiannual components are also included.
… 
Spatial distribution of the seasonal regimes of precipitation in Colombia. (left) Visual method of classification for IDEAM rain gauges. (middle) Same but the classification according to Fourier analysis using a threshold of 0.2 in the fraction of the variance explained for each component. (right) Same but using Climate Hazards Group Infrared Precipitation with Station data precipitation data set.
Spatial distribution of the seasonal regimes of precipitation in Colombia. (left) Visual method of classification for IDEAM rain gauges. (middle) Same but the classification according to Fourier analysis using a threshold of 0.2 in the fraction of the variance explained for each component. (right) Same but using Climate Hazards Group Infrared Precipitation with Station data precipitation data set.
… 
The fraction of variance explained (FVE) by the semiannual and annual components of the long‐term annual average cycle for the rain gauges in each of the five natural regions of Colombia. Rain gauge elevation above sea level is color coded according to the graphical scale.
+2
The fraction of variance explained (FVE) by the semiannual and annual components of the long‐term annual average cycle for the rain gauges in each of the five natural regions of Colombia. Rain gauge elevation above sea level is color coded according to the graphical scale.
… 
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Seasonality of Rainfall in Colombia
Viviana Urrea1, Andrés Ochoa1, and Oscar Mesa1
1Facultad de Minas, Departamento de Geociencias y Medio Ambiente, Universidad Nacional de Colombia Sede
Medellin, Medellin, Colombia
Abstract The knowledge of the annual cycle of rainfall is of primary concern for many socioeconomic
activities such as agricultural planning, electricity generation, and flood and other disaster management.
The annual cycle of rainfall in Colombia has been studied so far using monthly or quarterly information,
identifying zones with the unimodal regime (one wet season and one dry season) over the Caribbean, the
Amazon, and the Pacific regions and zones with the bimodal regime (two wet and two dry seasons) in the
Andes. This paper explores the annual rainfall cycle in Colombia on a daily basis using historical records of
1,706 rain gauges and the Climate Hazards Group Infrared Precipitation with Station data precipitation
data set. We found four types of annual precipitation regimes: unimodal, bimodal, mixed, and aseasonal.
The unimodal regime predominates in the low-altitude zones of the east and the north, the bimodal and
mixed regimes over the Andes mountain range, and the aseasonal in the Pacific region. These results
improve the statistical diagnosis of the spatial variability of the rainfall seasonality in Colombia. This
phenomenon, however, is still far from being fully understood in its hydroclimatic context. The annual
migration of the Intertropical Convergence Zone is not enough to explain the diversity of rainfall regimes
in Colombia. Local factors such as topography and land cover could play an important role in the
occurrence and duration of rainfall seasons.
1. Introduction
The fluctuation between rainy and dry periods is the main expression of climate seasonality in the tropics.
For instance, eighteen studies report the occurrence of two types of rainfall regimes in Colombia, those with
one dry season and one wet season and those with two dry and two wet seasons per year (e.g., Cochrane,
1825; Hettner, 1892; Mosquera, 1866; Wright, 1839). However, there is not a clear physical mechanism to
explain them. Several authors have pointed out the meridional migration of the Intertropical Convergence
Zone (ITCZ) as the main driver of the annual cycle of Colombia's hydroclimatology (Poveda & Mesa, 1997;
Poveda et al., 2006; Snow, 1976). The general picture set by the ITCZ is affected by other phenomena as
the Chocø low-level jet (Hoyos et al., 2017; Poveda & Mesa, 2000, 1999), the Caribbean jet (Hoyos et al.,
2017; Poveda et al., 2006; Poveda & Mesa, 1999), the atmospheric rivers (Montoya et al., 2001; Poveda et al.,
2014), the presence of the Andes mountain range (Garreaud, 2009; Guhl, 1974; Pagney, 1978), the advection
from the Amazon and Orinoco basins (Martínez et al., 2011; Poveda et al., 2006), and the El Niño–Southern
Oscillation (ENSO; Poveda et al., 2006, 2001).
The diagnosis of rainfall seasonality in Colombia has been made for a century using monthly or quarterly
data, identifying unimodal regions (with one dry season and one rainy season) and bimodal regions (two dry
and two rainy seasons). In fact, it is common to describe the rainy seasons in Colombia using the December
to February, March to May, June to August, and September to November quarters (see, e.g., Espinoza Villar
et al., 2009; Guhl, 1974; Martin, 1929; Mesa et al., 1997; Snow, 1976; Trojer, 1958, 1959). This monthly based
approach has two drawbacks: (1) it forces the duration of the seasons to be integer multiples of 1 month and
(2) the changes of a season can only occur at the end of the month.
In this paper, we overcome these two drawbacks by using daily rainfall time series. We use two data sources
(section 2): (a) the rain gauge network of the National Hydrological Service of Colombia (Instituto de
Hidrología, Meteorología y Estudios Ambientales, IDEAM) and (b) the Climate Hazards Group Infrared
Precipitation with Station data (CHIRPS v2.0; Funk et al., 2015) satellite product, with a spatial resolution of
0.05◦. We use a two-step method. The first step is to estimate the number of seasons at each site. This estima-
tion is done using the fraction of the variance explained (FVE) by the annual and semiannual components
revealed by the Fourier analysis of the long-term annual average cycle (LTAC). This approach has been used
RESEARCH ARTICLE
10.1029/2018WR023316
Key Points:
• Four types of annual rainfall regimes
were identified: unimodal, bimodal,
mixed, and aseasonal
• Unimodal regime predominates
in the north, east, and southeast;
bimodal in the Andes; and aseasonal
in the west
• Intertropical Convergence Zone
migration, the Choco and Caribbean
low-level jets, and topography are
major controls of the rain seasonality
Supporting Information:
• Supporting Information S1
•TableS1
•MovieS1
Correspondence to:
A. Ochoa,
aochoaj@unal.edu.co
Citation:
Urrea, V., Ochoa, A., & Mesa, O.
(2019). Seasonality of rainfall in
Colombia. Water Resources Research,
55, 4149–4162. https://doi.org/10.
1029/2018WR023316
Received 14 MAY 2018
Accepted 8 APR 2019
Accepted article online 23 APR 2019
Published online 22 MAY 2019
©2019. American Geophysical Union.
All Rights Reserved.
URREA ET AL. 4149
... The seasonality of these regions was previously described by [32,33,34], and [30]. They established that the rainfall varies spatially, identifying two homogeneous regions with different seasonal rainfall patterns. ...
... The rainfall patterns in both regions receive influences from the Intertropical Convergence Zone (ZCIT) migration, the complex region's orography, the Choco low-level jet, the Easterly Waves, the Atlantic multi-decadal oscillation (AMO) and the El Niño-Southern Oscillation (ENSO) phenomenon. More details about these physical and climatological explanations for the seasonality and spatial distribution of rainfall have been described by [31][32][33][35][36][37][38]. ...
... The daily rainfall data accumulated monthly between 1983 and 2019 was used. The CHIRPS dataset was previously used in Colombia by [46] to study historical rainfall, by [47] to analyze trends, by [48] to estimate the water balance in the Pacific Basins in Colombia, and by [33] to research seasonality. ...
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Long and temporal time-consistency rainfall time series are essential for studying climate; nevertheless, raingauge stations are unevenly distributed across southwestern Colombia. This research paper assesses the consistency of the satellite rainfall estimate from Climate Hazards Group Infrared Precipitation (CHIRPS) via pixel-to-point comparison with 46 observed monthly rainfall time series using four pairwise metrics and Combined Principal Component Analysis (CPCA). Two Combined Principal Components (CPC) were also used to determine the relationship with the Sea Surface Temperature (SST) through simultaneous linear correlation maps. The results showed that CHIRPS has a better performance in the Andean region than in the Pacific region. The correlation between CPC1 (CPC2) and SST showed a typical El Niño Southern Oscillation pattern with an inverse (direct) relationship between the rainfall in the Andean (Pacific) Region. Finally, our results validate that CHIRPS can be included in further studies of the spatiotemporal dynamics of rainfall in Southwestern Colombia.
... According to Urrea et al. [41], the country has four types of annual precipitation regimes: unimodal, bimodal, mixed, and aseasonal or seasonally invariant. The unimodal regime (one rainy season and one dry) is registered mainly in the Orinoco, Amazon, and Caribbean regions, probably related to the South American monsoon, whereas the bimodal regime occurs predominantly in the Andean region due to the mountainous areas and the double pass of the ITCZ. ...
... On the other hand, in transition zones between unimodal and bimodal regimes, a mixed regime is registered. Furthermore, the aseasonal regimes are evidenced in some areas of the Pacific region due to the alternation of the moisture supply by the low-level Chocó and Caribbean jets [41][42][43]. ...
... On the other hand, in transition zones betw modal and bimodal regimes, a mixed regime is registered. Furthermore, the a regimes are evidenced in some areas of the Pacific region due to the alternatio moisture supply by the low-level Chocó and Caribbean jets [41][42][43]. Figure 2 shows the monthly mean precipitation maps for the 1981-2018 per the CHIRPS database; in all months, the physiographic influence of the Colomb tory is observed, mainly dominated by the three branches of the Andes mountai According to Estupiñan [44], the bimodality or unimodality of rainfall can be r the ITCZ latitudinal displacement such that, in the summer of the southern hem (December-January-February (DJF)), the ITCZ is located south of the equator, ge higher precipitation in latitudes southern than 2° N (Figure 2a-c). In the March May (MAM) period, the ITCZ shifts northward, causing increased precipitation latitudes 2°-7° N (Figure 2d-f), during the northern hemisphere summer (June-J gust (JJA)), the ITCZ reaches its greatest displacement towards the north of the generating a reduction in rainfall, mainly in the Andean region (Figure 2g-i). ...
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The Andes mountain range divides Colombia into various climatic regions over the country, as the Andean, Caribbean, Pacific, Amazon, and Orinoco regions. Given this scenario, knowing the current change in total precipitation and their extremes values are relevant. In this study, the main goal is to assess the spatio-temporal trends of heavy and intense rainfall at a seasonal scale during the last 38 years (1981–2018) using the trend empirical orthogonal function (TEOF). An increase in maximum precipitation during five consecutive days (RX5day), Simple daily intensity index (SDII), and the number of days with precipitation above 20 mm (R20mm) and 30 mm (R30mm) during December–February and March–May was observed in most of the Colombian territory, except for the Amazon region for RX5day. A decrease in total rainfall in June–August was observed in the Andean, the Caribbean, and southern Pacific regions, while, in the northern Pacific, it increased, consistent with the trend patterns of RX5day, SDII, and R20mm. During September–November, there was a reduction in rainfall in the Amazon region and the South Pacific, and an increase in RX5day, SDII, R20mm, and R30mm in the Andean, the Caribbean, and North Pacific regions. The TEOF showed more pronounced spatial trend patterns than those obtained with the traditional Mann–Kendall test. The findings offer a better understanding of the climate extremes impacts in tropical latitudes and help planners to implement measures against the future effects of climate change
... These two jet streams transport humidity from the Atlantic and the Pacific Oceans to the Chocó region, respectively. Finally, the proximity to the Pacific Ocean of both the coastal Baudó Range and the Western Andean Cordillera induces copious orographic rains throughout the region by the Föhn's effect (David et al. 2014;Urrea et al. 2019). ...
... Climatologists have described the center of the Chocó as an aseasonal zone according to the mean rains of each month (Guzmán et al. 2014) or the daily rains (Urrea et al. 2019). In this aseasonal zone, there are 12 localities with records of more than 8000 mm of mean annual precipitation, 2 with more than 12,000 mm. ...
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Key message Isotope variation (δ¹⁸O) in wood suggests new insights on growth rhythms in trees growing in tropical forest with extremely high precipitation, without seasonal droughts or flooding. Abstract It is well known that growth-limiting factors such as seasonal droughts can induce periodicities in woody tissue formation of tropical trees. In regions without seasonal droughts or flooding but sufficient water for photosynthesis (ever-wet tropical forests), rhythmic growth has been previously reported; however, triggering factors remain little explored. Our objective was to establish tree-ring frequency and probable growing season by analysis of the intra-annual variability of isotopic ratios in cellulose (δ¹⁸Ocellulose and δ¹³Ccellulose) and relationships with environmental variables in two tree species (Humiriastrum procerum and Virola dixonii) growing in an ever-wet tropical forest (Choco region of Colombia, precipitation 7200 mm year⁻¹, mean annual temperature 25.9 °C), located close to the Pacific Ocean at ca 3° 57′ 12.54″ N–76° 59′ 27.96″ W. Here, we report annual rhythmic growth evidenced by radiocarbon analysis, leaf phenology, dendrometer records, and stable-isotope variation in cellulose. All evidence points to the probable growing season occurring during the least rainy months for both species. While intra-annual δ¹⁸Ocellulose values follow a rhythmic variation, δ¹³Ccellulose variations show a less clear pattern, probably due to deciduity and remobilization of non-structural carbon stored in previous growing stages. Furthermore, δ¹⁸Ocellulose covary with relative humidity, vapor pressure deficit, short-wave solar radiation, and temperature during the least rainy months. In contrast, δ¹³Ccellulose values were not significantly correlated with environmental variables. Our results show that stable-isotope variations in tree rings, even under ever-wet conditions, are valuable for understanding drivers of tropical tree growth in such conditions.
... Duración: 91 a 182 días. Urrea et al. (2019) Región Pacífico no tiene predominancia de ningún régimen. ...
... Zona norte: régimen unimodal. Urrea et al. (2019) Figura 7. Variabilidad interanual, fases del ENSO en las estaciones Sautatá. ...
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... D'Odorico et al., 2000). About tropical Andean rain, one of its main influencing sinoptic processes (ENSO) is quasi periodic, and its degree of influence fall from west to east and affects mostly river flow instead rain (Poveda & Mesa, 1997); moreover some timescales are interrelated, e.g. with ENSO affecting the seasonal (Urrea et al., 2019) and this one affecting the hourly (Bedoya-Soto et al., 2019). ...
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Mountain basins are open dynamic systems which organize at multiple scales to transform hillslope sediment supply to fluvial sediment transport. In a given river reach, its form and sediment regime depend on basin processes and are contingent to geomorphic history. Lack of such information makes modelling the way to estimate this spatiotemporal context. However, there is a gap of combining spatiotemporal variability of hydrology and landslides sediment supply with its effect: the feedback between channel form and sediment transport. Hillslope and fluvial modules of a new model called Fluvial Hydro-Geomorphology Model (FHGM) are produced which, in hollows and river reaches that are deformable, encapsulates complexity via parameterization or random forcing. FHGM solves responses to every major rain event, and accumulate them in decadal timescale, to include occurrence of channel forming floods as well as landslides with varied sizes and source zones. FHGM landslides module reproduces power law spatial distribution of landslide volumes, as well as magnitud and frecuency of sediment supply. FHGM fluvial module, calibrated with a new gravel flume experiment, reproduces a broad range of morphologic conditions, from incised to clogged, and produces mean bankfull capacity consistent to mean maximum annual flood and with empirical dimensionless hydraulic geometry patterns for channel depth and width. This work shows how mountain basins organize to minimize the duration of formative events, by editing channels capacity and deforming sediment storages to recover stability and structure; a resilience akin to living beings.
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This paper introduces an objective definition of local onset and demise of the Indian summer monsoon (ISM) at the native grid of the Indian Meteorological Department’s rainfall analysis based on more than 100 years of rain gauge observations. The variability of the local onset/demise of the ISM is shown to be closely associated with the All India averaged rainfall onset/demise. This association is consistent with the corresponding evolution of the slow large-scale reversals of upper air and ocean variables that raise the hope of predictability of local onset and demise of the ISM. The local onset/demise of the ISM also show robust internannual variations associated with El Nino and the Southern Oscillation and Indian Ocean dipole mode. It is also shown that the early monsoon rains over northeast India has a predictive potential for the following seasonal anomalies of rainfall and seasonal length of the monsoon over rest of India.
Moisture origin and transport processes in Colombia, northern South America
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We assess the spatial structure of moisture flux divergence, regional moisture sources and transport processes over Colombia, in northern South America. Using three independent methods the dynamic recycling model (DRM), FLEXPART and the Quasi-isentropic back-trajectory (QIBT) models we quantify the moisture sources that contribute to precipitation over the region. We find that moisture from the Atlantic Ocean and terrestrial recycling are the most important sources of moisture for Colombia, highlighting the importance of the Orinoco and Amazon basins as regional providers of atmospheric moisture. The results show the influence of long-range cross-equatorial flow from the Atlantic Ocean into the target region and the role of the study area as a passage of moisture into South America. We also describe the seasonal moisture transport mechanisms of the well-known low-level westerly and Caribbean jets that originate in the Pacific Ocean and Caribbean Sea, respectively. We find that these dynamical systems play an important role in the convergence of moisture over western Colombia.
A high-resolution history of the South American Monsoon from Last Glacial Maximum to the Holocene
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Full-text available
  • Mar 2017
The exact extent, by which the hydrologic cycle in the Neotropics was affected by external forcing during the last deglaciation, remains poorly understood. Here we present a new paleo-rainfall reconstruction based on high-resolution speleothem δ18O records from the core region of the South American Monsoon System (SAMS), documenting the changing hydrological conditions over tropical South America (SA), in particular during abrupt millennial-scale events. This new record provides the best-resolved and most accurately constrained geochronology of any proxy from South America for this time period, spanning from the Last Glacial Maximum (LGM) to the mid-Holocene.
The onset and cessation of seasonal rainfall over Africa
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Full-text available
  • Oct 2016
Variation in the seasonal cycle of African rainfall is of key importance for agriculture. Here, an objective method of determining the timing of onset and cessation is, for the first time, extended to the whole of Africa. The method is applied to five observational datasets and the ERA-Interim reanalysis. Compatibility with known physical drivers of African rainfall, consistency with indigenous methods, and generally strong agreement between satellite-based rainfall datasets confirm the method is capturing the correct seasonal progression of African rainfall. The biannual rainfall regime is correctly identified over the coastal region of Ghana and the Ivory Coast. However, the ERA-Interim reanalysis exhibits timing biases over areas with two rainy seasons, and both ERA-Interim and the ARCv2 observational dataset exhibit some inconsistent deviations over West Africa. The method can be used to analyze both seasonal - interannual variability and long-term change. Over East Africa, we find that failure of the rains and subsequent humanitarian disaster is associated with shorter as well as weaker rainy seasons, e.g. on average the long rains were 11 days shorter in 2011. Cessation of the short rains over this region is 7 days later in El Niño and 5 days earlier in La Niña years with only a small change in onset date. The methodology described in this paper is applicable to multiple datasets and to large regions, including those that experience multiple rainy seasons. As such, it provides a means for investigating variability and change in the seasonal cycle over the whole of Africa. http://onlinelibrary.wiley.com/doi/10.1002/2016JD025428/full
The climate hazards infrared precipitation with stations - A new environmental record for monitoring extremes
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Full-text available
  • Dec 2015
The Climate Hazards group Infrared Precipitation with Stations (CHIRPS) dataset builds on previous approaches to ‘smart’ interpolation techniques and high resolution, long period of record precipitation estimates based on infrared Cold Cloud Duration (CCD) observations. The algorithm i) is built around a 0.05° climatology that incorporates satellite information to represent sparsely gauged locations, ii) incorporates daily, pentadal, and monthly 1981-present 0.05° CCD-based precipitation estimates, iii) blends station data to produce a preliminary information product with a latency of about 2 days and a final product with an average latency of about 3 weeks, and iv) uses a novel blending procedure incorporating the spatial correlation structure of CCD-estimates to assign interpolation weights. We present the CHIRPS algorithm, global and regional validation results, and show how CHIRPS can be used to quantify the hydrologic impacts of decreasing precipitation and rising air temperatures in the Greater Horn of Africa. Using the Variable Infiltration Capacity model, we show that CHIRPS can support effective hydrologic forecasts and trend analyses in southeastern Ethiopia.
Characterizing the onset and demise of the Indian summer monsoon: Indian Summer Monsoon
Article
An objective index of the onset and demise of the Indian summer monsoon (ISM) is introduced. This index has the advantage of simplicity by using only one variable, which is the spatially averaged all-India rainfall, a reliably observed quantity for more than a century. The proposed onset index is shown to be insensitive to all historic false onsets. By definition, now the seasonal mean rainfall anomalies become a function of variations in onset and demise dates, rendering their monitoring to be very meaningful. This new index provides a comprehensive representation of the seasonal evolution of the ISM by capturing the corresponding changes in large-scale dynamic and thermodynamic variables. We also show that the interannual variability of the onset date of the ISM is associated with El Niño-Southern Oscillation (ENSO) with early (late) onsets preceded by cold (warm) ENSO.
La meteorología y climatología de la vertiente del pacífico Colombiano
Article
  • Jan 1958
Buena parte del entendimiento que hoy tenemos sobre la variabilidad espacial y temporal de los procesos que definen el clima (largo plazo) y el tiempo atmosférico (corto plazo) en Colombia, se deben a H. Trojer. En particular, en este trabajo se discuten los principales mecanismos dinámicos y termodinámicos asociados con ambas escalas de tiempo, y es pionero en distinguir entre los fenómenos que dan lugar al clima, como la oscilación de la Zona de Convergencia Intertropical, y su influencia en el ciclo anual de la precipitación, de aquellos efectos locales causantes del tiempo atmosférico como la topografía y los sistemas locales de circulación (tierra-mar o valle-montaña).La vertiente del Pacífico Colombiano es uno de los lugares más lluviosos del planeta, con precipitaciones promedias entre 8.000 y 13.000 mm por año. A partir de registros de diversas variables meteorológicas, este trabajo de Trojer discute la dinámica temporal y espacial de la meteorología y el clima de esta fascinante región de Colombia. Además, es pionero en temas como: (1) el ciclo diurno de la precipitación en Colombia, al evidenciar su alta variabilidad en las zonas de montaña, al estudiar su comportamiento en los distintos meses del año y su relación con la latitud, y al descubrir los mecanismos causantes del carácter bimodal de dicho ciclo diurno. (2) El ciclo anual de intensidad, frecuencia y duración de aguaceros. (3) El primer mapa de la distribución de la lluvia promedio anual sobre la región de estudio, al evidenciar una fuerte zonificación norte-centrosur. (4) La influencia entre la altura topográfica y las precipitaciones anuales. (5) Vincular dos variables que representan el balance de agua y el balance de energía, tales como la precipitación (P) y el brillo solar (B) con el fin de establecer un cociente que permitiera una zonificación climática, un tema de fundamental relevancia en la hidroecología actual.Germán Poveda, Ph.D.Miembro de Número
Rainfall hotspots over the southern tropical Andes: Spatial distribution, rainfall intensity, and relations with large-scale atmospheric circulation: Rainfall hotspots over the southern tropical Andes
Article
  • Apr 2015
The Andes/Amazon transition is among the rainiest regions of the world and the interactions between large-scale circulation and the topography that determine its complex rainfall distribution remain poorly known. This work provides an in-depth analysis of the spatial distribution, variability, and intensity of rainfall in the southern Andes/Amazon transition, at seasonal and intraseasonal time scales. The analysis is based on comprehensive daily rainfall data sets from meteorological stations in Peru and Bolivia. We compare our results with high-resolution rainfall TRMM-PR 2A25 estimations. Hotspot regions are identified at low elevations in the Andean foothills (400–700 masl) and in windward conditions at Quincemil and Chipiriri, where more than 4000 mm rainfall per year are recorded. Orographic effects and exposure to easterly winds produce a strong annual rainfall gradient between the lowlands and the Andes that can reach 190 mm/km. Although TRMM-PR reproduces the spatial distribution satisfactorily, it underestimates rainfall by 35% in the hotspot regions. In the Peruvian hotspot, exceptional rainfall occurs during the austral dry season (around 1000 mm in June–July–August; JJA), but not in the Bolivian hotspot. The direction of the low-level winds over the Andean foothills partly explains this difference in the seasonal rainfall cycle. At intraseasonal scales in JJA, we found that, during northerly wind regimes, positive rainfall anomalies predominate over the lowland and the eastern flank of the Andes, whereas less rain falls at higher altitudes. On the other hand, during southerly regimes, rainfall anomalies are negative in the hotspot regions. The influence of cross-equatorial winds is particularly clear below 2000 masl.
Aspects climatiques des Andes de Colombie (Climatological aspects of Colombian Andes)
Article
  • Jan 1978
- The Andes in Colombia receive a lut of rain. This is also true of their sides, along the Pacific, the Llanos and the Amazon-basin. They experience a precipitation optimum as well inside the mountain ranges as outside.. The seasonal march of rainfall provides constant moisture in the Western Lowlands and two rainy seasons inside the Andes and one rainy season alternating with a dry season in the East. (In the Llanos and the Amazon-basin). Precipitations result from the presence of the ITC and of a low-pressure trend along the Pacific.