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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
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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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... 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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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
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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.
Article
- 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.