Reduced Wet-Season Length Detected by Satellite Retrievals of Cloudiness over Brazilian Amazonia: A New Methodology

This study investigates the variability of the seasonal cycle of convection in the Brazilian Amazon basin during the last decades, and examines physical mechanisms that potentially trigger these modifications. A new methodology to evaluate the onset and length of the rainy season using long-term cloud fraction observations from geostationary satellites is proposed and the connection between cloud cycle variability, surface properties, and thermodynamic and dynamic conditions is explored. The results show that cloud cover has significantly decreased over the last decades. The decline in cloudiness is steeper at 1200 UTC (0800 LT), when a trend of up to −6% decade−1 is observed over the central and eastern Amazon. High-cloud-cover reduction is the major contributor to the observed decline in total cloud fraction. Delayed onsets and a reduction of up to 4 days yr−1 in the northern and central Amazon wet-season length are observed. Correlation analyses indicate that the El Niño phenomenon affects the interannual variability of cloudiness in the Amazon, leading to delayed onset and early demise of the rainy season. The tropical South Atlantic, the Pacific warm pool, and the North Atlantic tripole also play a small, but significant, role in the Amazon’s cloudiness variability. The decrease in cloudiness over the Amazon basin reduces the amount of solar radiation reflected back to space while increasing irradiance at the surface. This local warming alters surface heat fluxes and the atmospheric thermodynamic profile, further affecting cloud development. The strong tendencies reported here indicate a significant shift in the Amazonian hydroclimate during the last few decades.

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The Major Floods in the Amazonas River and Tributaries (Western Amazon Basin) during the 1970–2012 Period: A Focus on the 2012 Flood*

Journal of Hydrometeorology ◽

10.1175/jhm-d-12-0100.1 ◽

2013 ◽

Vol 14 (3) ◽

pp. 1000-1008 ◽

Cited By ~ 76

Author(s):

Jhan Carlo Espinoza ◽

Josyane Ronchail ◽

Frédéric Frappart ◽

Waldo Lavado ◽

William Santini ◽

...

Keyword(s):

Amazon Basin ◽

Wave Train ◽

La Niña ◽

Wet Season ◽

Extreme Floods ◽

The North ◽

La Nina ◽

Terrestrial Water ◽

Major Floods ◽

La Nina Event

Abstract In this work, the authors analyze the origin of the extreme floods in the Peruvian Amazonas River during the 1970–2012 period, focusing on the recent April 2012 flooding (55 400 m3 s−1). Several hydrological variables, such as rainfall, terrestrial water storage, and discharge, point out that the unprecedented 2012 flood is mainly related to an early and abundant wet season over the north of the basin. Thus, the peak of the Marañón River, the northern contributor of the Amazonas, occurred sooner than usual (in April instead of May), coinciding with the peak of the Ucayali River, the southern contributor. This concomitance caused a dramatic flood downstream in the Peruvian Amazonas. These results are compared to the amplitude and timing of the three most severe extreme floods (1970–2011). The analysis of the climatic features related to the most important floods (1986, 1993, 1999, and 2012) suggests that they are characterized by a La Niña event, which originates a geopotential height wave train near the ground, with positive anomalies over the subtropical South and North Pacific and Atlantic and over southeastern South America. These patterns contribute to 1) the origin of an abundant humidity transport flux from the tropical North Atlantic and the Caribbean Sea toward the northwestern Amazon and 2) the maintenance of the monsoon flux over this region. They both favor a strong convergence of humidity in the northern Amazonas basin. Finally, the authors suggest that the intensity of floods is more likely related to an early La Niña event (as observed during the 2011/12 season), early rainfall, and simultaneous peaks of both tributaries of the Amazonas River.

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PADRÕES ATMOSFÉRICOS E OCEÂNICOS ASSOCIADOS A EVENTOS EXTREMOS NA BACIA AMAZÔNICA: UMA ANÁLISE DE COMPOSIÇÃO BASEADA NOS EPSÓDIOS SECOS DE 1982/83, 2004/05 E 2009/10

Ciência e Natura ◽

10.5902/2179460x22687 ◽

2017 ◽

Vol 39 (2) ◽

pp. 423

Author(s):

Franci Flores Vargas ◽

José Augusto Paixão Veiga

Keyword(s):

South America ◽

Rainy Season ◽

Amazon Basin ◽

Moisture Flux ◽

Northern Region ◽

Northeastern Brazil ◽

Specific Humidity ◽

Trade Winds ◽

The North ◽

Variable Precipitation

This study aimed to determine the atmospheric and oceanic patterns related to changes in precipitation over the Amazon basin during the episodes of extreme drought occurred in the years of 1982/83, 2004/2005 and 2009/10. Data from the zonal and meridional components of the wind vector, wind speed, omega, specific humidity, precipitation and sea surface temperature was used. The data was obtained from the reanalysis-2 NCPE/NCAR (except for the variable precipitation which was obtained from the CMAP). The anomalous composition method was used to determine the atmospheric and ocean fields that were characteristic of episodes of intense drought. The results show a deficit in rainfall in the rainy pre-season (SON) in part of the northern region of South America and northeastern Brazil. The lower level of rainfall also persists during the rainy season (December to April). Associated with these anomalous patterns of rainfall, positive anomalies of SST were observed which were similar to El Niño events, followed by anomalous subsidence in the Amazon. In the rainy pre-season, wind divergence over the state of Amazonas and the north of South America was observed. During the rainy season, the divergence in streamlines shows the weakening of the northeast trade winds. In addition, the anomalous divergence of vertically integrated moisture flux reveals consistency with rainfall deficits in theipre and rainy season in the Amazon basin.

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Onset and End of the Rainy Season in South America in Observations and the ECHAM 4.5 Atmospheric General Circulation Model

Journal of Climate ◽

10.1175/jcli4122.1 ◽

2007 ◽

Vol 20 (10) ◽

pp. 2037-2050 ◽

Cited By ~ 70

Author(s):

Brant Liebmann ◽

Suzana J. Camargo ◽

Anji Seth ◽

José A. Marengo ◽

Leila M. V. Carvalho ◽

...

Keyword(s):

Rainy Season ◽

General Circulation ◽

Rain Rate ◽

Atmospheric General Circulation Model ◽

Circulation Model ◽

Season Length ◽

Wet Season ◽

Atmospheric General Circulation ◽

Annual Total ◽

Sst Anomalies

Abstract Rainfall in South America as simulated by a 24-ensemble member of the ECHAM 4.5 atmospheric general circulation model is compared and contrasted with observations (in areas in which data are available) for the period 1976–2001. Emphasis is placed on determining the onset and end of the rainy season, from which its length and rain rate are determined. It is shown that over large parts of the domain the onset and ending dates are well simulated by the model, with biases of less than 10 days. There is a tendency for model onset to occur early and ending to occur late, resulting in a simulated rainy season that is on average too long in many areas. The model wet season rain rate also tends to be larger than observed. To estimate the relative importance of errors in wet season length and rain rate in determining biases in the annual total, adjusted totals are computed by substituting both the observed climatological wet season length and rate for those of the model. Problems in the rain rate generally are more important than problems in the length. The wet season length and rain rate also contribute substantially to interannual variations in the annual total. These quantities are almost independent, and it is argued that they are each associated with different mechanisms. The observed onset dates almost always lie within the range of onset of the ensemble members, even in the areas with a large model onset bias. In some areas, though, the model does not perform well. In southern Brazil the model ensemble average onset always occurs in summer, whereas the observations show that winter is often the wettest period. Individual members, however, do occasionally show a winter rainfall peak. In southern Northeast Brazil the model has a more distinct rainy season than is observed. In the northwest Amazon the model annual cycle is shifted relative to that observed, resulting in a model bias. No interannual relationship between model and observed onset dates is expected unless onset in the model and observations has a mutual relationship with SST anomalies. In part of the near-equatorial Amazon, there does exist an interannual relationship between onset dates. Previous studies have shown that in this area there is a relationship between SST anomalies and variations in seasonal total rainfall.

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Change of the Rainfall Seasonality Over Central Peruvian Andes: Onset, End, Duration and Its Relationship With Large-Scale Atmospheric Circulation

Climate ◽

10.3390/cli8020023 ◽

2020 ◽

Vol 8 (2) ◽

pp. 23 ◽

Cited By ~ 1

Author(s):

Lucy Giráldez ◽

Yamina Silva ◽

Ricardo Zubieta ◽

Juan Sulca

Keyword(s):

Rainy Season ◽

Large Scale ◽

Amazon Basin ◽

Late Onset ◽

Caribbean Region ◽

Equatorial Atlantic ◽

Tropical Andes ◽

The South ◽

Wet Season ◽

Peruvian Andes

Changes of the onset dates, end dates, and duration of the rainy season over central Peruvian Andes (Mantaro river basin, MRB) could severely affect water resources management and the main economic activities (e.g., rainfed agriculture, raising cattle, among others). Nonetheless, these changes have not been documented for the Tropical Andes. To asses that, we used daily datasets of observed rainfall during the 1965–2013 period. For this period, the average onset (end) date of the rainy season over the MRB occurs in the pentad 17 (19–23 September) [pentad 57 (7–11 April)]. The duration of the rainy season mainly is modulated by the onset dates due to it has higher variability than end dates. There is a reduction of 3 days/decade in the duration of wet season over the MRB for the last four decades due to the delay of the onset days. Furthermore, El Niño favors late-onset and early end of the rainy season, while La Niña favors early onset and late end of the rainy season in the MRB. Onset dates are related to the propagation of the convective region of the South American Monsoon System (SAMS), from the Caribbean region toward the central Amazon basin. Early (late)-onset days are associated with a southward (northward) shift of the South Atlantic Convergence Zone (SACZ) and weak (strong) convection over equatorial Atlantic that induces the southernmost propagation (eastward shift) of the SAMS.

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Interannual variability of Tropical Atlantic and its influence on drought and flood events in the Amazon Basin

10.5194/egusphere-egu2020-146 ◽

2020 ◽

Author(s):

Katherine Lisbeth Ccoica López ◽

Ricardo Hallak ◽

Victor Raúl Chavez Mayta

Keyword(s):

North Atlantic ◽

Rainy Season ◽

Amazon Basin ◽

South Atlantic ◽

Sea Surface ◽

Tropical Atlantic ◽

Flood Events ◽

Drought And Flood ◽

The North ◽

Tropical North Atlantic

The Tropical Pacific and Tropical Atlantic Ocean modulate the interannual precipitation over the Amazon region and the decadal and interdecadal variation as well. During El Ni&#241;o Southern Oscillation (ENSO), below-average rainfall is recorded in the North and Northeast of the Basin, while deficit of precipitation is observed in the West and South. On the other hand, during La Ni&#241;a years, rainfall is above of normal in the North and Northeast of Amazon Basin. However, there are also drought events, such as in 1964 and 2005, unrelated to the El Ni&#241;o event, but influenced by warm conditions in the Tropical North Atlantic. In fact, the exceptional drought recorded in 2010 was influenced by a combined effect of the El Ni&#241;o event during the peak of rainy season, followed by warm conditions in the Tropical North Atlantic during final of rainy season and dry season.Therefore, the main aim of this study is exploring the Atlantic Sea Surface Temperature (SST) condition in modulating patterns that influence the development of drought and flood events in the Amazon Basin. First of all, the Atlantic Ocean is divided into Tropical North Atlantic (TNA), Tropical South Atlantic (TSA) and Subtropical South Atlantic (STSA), to analyze the behavior of each region separately. Atlantic Index, in each region, is the first principal component (PC1) time series, which comes from the empirical orthogonal function (EOF) analysis applied to Hadley Center Global Sea Ice and Sea Surface Temperature (HadISST) dataset for the 1870-2107 period. The Tropical North Atlantic, Tropical South Atlantic and Subtropical South Atlantic indices show the main years when drought and flood events reaching the Amazon Basin (droughts in 2005, 2010 and 2015, and floods in 2009 and 2012, mainly), and 5-years moving correlations indicate that these three ocean basin have been coupled and decoupled periodically each other in the last century.The equatorial Pacific, North Atlantic and South Atlantic indices were also correlated with rainfall over the Amazon for three databases: the Tropical Rainfall Mission Measurements (TRMM), the Global Precipitation Climatology Centre (GPCC) and the HyBAm Observed Precipitation. All three databases showed the same results. An increase of the SST in Eastern Pacific influences in low precipitation over the central and west of the Amazon Basin during the rainy season (December to February), increase of the SST in Central Pacific influences for droughts over the northeast region and the TSA influences in the central Amazon. Increase of the SST in TNA and STSA influences mainly in the dry season (May to September), intensifying it. TNA is responsible for precipitation below normal over the central and west Amazon Basin, while STSA only influences in the central region of the basin. Finally, analysis of extreme events indicate that droughts and floods in the Amazon are intensified (de-intensified) if we consider warm (cold) phases of the AMO (Atlantic Multidecadal Oscillation) and the PDO (Pacific Decadal Oscillation).

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Vegetation indices as proxies for spatio-temporal variations in water availability in the Rio Santa valley (Peruvian Andes)

10.5194/esd-2021-60 ◽

2021 ◽

Author(s):

Lorenz Hänchen ◽

Cornelia Klein ◽

Fabien Maussion ◽

Wolfgang Gurgiser ◽

Pierluigi Calanca ◽

...

Keyword(s):

Water Availability ◽

Rainy Season ◽

Vegetation Indices ◽

Growing Season ◽

Dry Season ◽

Season Length ◽

Wet Season ◽

Peruvian Andes ◽

Spatio Temporal ◽

Semi Arid

Abstract. In the semi-arid Peruvian Andes, the growing season is mostly determined by the timing of the onset and retreat of the wet season, to which annual crop yields are highly sensitive. Recently, local farmers in the Rio Santa basin (RSB) reported decreasing predictability of the onset of the rainy season and further challenges related to changes in rainfall characteristics. Previous studies based on time series of local rain gauges however, did not find any significant changes in either the timing or intensity of the wet season. Both in-situ and satellite rainfall data for the region lack the necessary spatial resolution to capture the highly variable rainfall distribution typical for complex terrain, and are often questionable in terms of quality and temporal consistency. To date, there remains considerable uncertainty in the RSB regarding hydrological changes over the last decades. In this study, we overcome this limitation by exploiting satellite-derived information on vegetation greenness to reveal a robust and highly resolved picture of recent changes in rainfall and vegetation phenology across the region: As the semi-arid climate causes water availability (i.e. precipitation) to be the key limiting factor for plant growth, patterns of precipitation occurrence and the seasonality of vegetation indices (VIs) are tightly coupled. Therefore, VIs can serve as an integrated proxy of rainfall. By combining MODIS Aqua and Terra VIs for 2000–2020 and several datasets of precipitation, we explore recent spatio-temporal changes in vegetation and water availability. Furthermore, we examine their links to El Niño Southern Oscillation (ENSO). While different rainfall datasets tend to be incoherent in the period of observation, we find significant greening over the majority of the RSB domain in VI data, particularly pronounced during the dry season (Austral winter). This indicates an overall increase of plant available water over time. The rainy season onset and consequently the start of the growing season (SOS) exhibits high inter-annual variability and dominates the growing season length (LOS). The end of the growing season (EOS) is significantly delayed in the analysis which matches the observed dry-season greening. By partitioning the results into periods of three stages of ENSO (neutral, Niño, Niña), we find an earlier SOS and an overall increased season length in years associated with El Niño. However, the appearance of Niño/Niña events during the analysed period cannot explain the observed greening and delayed EOS. While our study could not corroborate anecdotal evidence for recent changes in the SOS, we confirm that the SOS is highly variable and conclude that rainfed farming in the RSB would profit from future efforts being directed towards improving medium-range forecasts of the rainy season onset.

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Observations of Cloud, Radiation, and Surface Forcing in the Equatorial Eastern Pacific

Journal of Climate ◽

10.1175/2007jcli1757.1 ◽

2008 ◽

Vol 21 (4) ◽

pp. 655-673 ◽

Cited By ~ 18

Author(s):

C. W. Fairall ◽

Taneil Uttal ◽

Duane Hazen ◽

Jeffrey Hare ◽

Meghan F. Cronin ◽

...

Keyword(s):

Radiative Forcing ◽

Marine Boundary Layer ◽

Surface Flux ◽

Cloud Fraction ◽

Heat Fluxes ◽

Eastern Pacific ◽

Cloud Base ◽

Tropical Eastern Pacific ◽

Cloud Forcing ◽

The North

Abstract In this paper the authors report on a study of cloud and surface flux processes in the tropical eastern Pacific Ocean based on a series of ship-based cloud and flux measurements made during fall (1999–2002) and spring (2000–02) maintenance cruises along the 95° and 110°W Tropical Atmosphere Ocean (TAO) buoy lines between 8°S and 12°N. The year-to-year and seasonal variabilities of many of the meteorological and oceanic means are relatively small. However, notable seasonal variability is found in the northern branch of the intertropical convergence zone, the north–south sea surface temperature gradient, and heat fluxes north of the equator. In the fall, the strengthening of the north–south SST contrast enhances convective activity (more and deeper clouds, precipitation, southerly inflow) in the area around 6°N, 95°W; diurnal variations of low cloud fraction were weak. Spring cloud fraction varied significantly over the diurnal cycle with substantially lower cloud fraction during the day south of 5°N. Relatively low average cloud-base heights around the equator are due to chilling of the marine boundary layer over the cold tongue. Cloud radiative forcing strongly correlates with cloud fraction; clouds in the observation region cool the surface by about 40 W m−2 in both seasons. Cloud forcing estimates from the ship data, the TAO buoys, and International Satellite Cloud Climatology Project (ISCCP) products were combined to form a consensus observation dataset that is compared with the second NCEP reanalysis (NCEP-2) and 40-yr ECMWF Re-Analysis (ERA-40) cloud forcing values. The reanalysis products were within 10 W m−2 of the observations for IR cloud forcing but substantially overestimated the solar cloud forcing, particularly in spring.

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Dactylogyrids (Platyhelminthes, Monogenoidea) from the gills of Hoplias malabaricus (Characiformes: Erythrinidae) from coastal rivers of the Oriental Amazon Basin: species of Urocleidoides and Constrictoanchoratus n. gen.

Journal of Helminthology ◽

10.1017/s0022149x17000384 ◽

2017 ◽

Vol 92 (3) ◽

pp. 353-368 ◽

Cited By ~ 2

Author(s):

K.D.C. Ferreira ◽

A.R.O. Rodrigues ◽

J.-M. Cunha ◽

M.V. Domingues

Keyword(s):

New Species ◽

Amazon Basin ◽

Copulatory Organ ◽

Ventral Anchor ◽

Mato Grosso ◽

Hoplias Malabaricus ◽

The North ◽

Coastal Rivers ◽

Upper Paraná River Floodplain ◽

Host Parasite

AbstractFive species of Urocleidoides (one new) and two new species of Constrictoanchoratus n. gen. are described in this study. All were collected from the gills of Hoplias malabaricus (Characiformes: Erythrinidae) captured in six localities of coastal rivers of the north-eastern sector the State of Pará (Oriental Amazon): Urocleidoides brasiliensis Rosim, Mendoza-Franco & Luque, 2011; Urocleidoides bulbophallus n. sp.; Urocleidoides cuiabai Rosim, Mendoza-Franco & Luque, 2011; Urocleidoides eremitus Kritsky, Thatcher & Boeger, 1986; Urocleidoides malabaricusi Rosim, Mendoza-Franco & Luque, 2011; Constrictoanchoratus lemmyi n. gen. n. sp.; and Constrictoanchoratus ptilonophallus n. gen. n. sp. This is the first reported occurrence of the four previously described species of Urocleidoides parasitizing H. malabaricus from streams in the Oriental Amazon Basin. The analysis of voucher specimens of U. eremitus parasitizing the gills of H. malabaricus from the Upper Paraná River floodplain in the limits of States of Paraná and Mato Grosso do Sul, Brazil, indicates that these specimens are members of a new species of Urocleidoides, described here as Urocleidoides paranae n. sp. Constrictoanchoratus n. gen. is proposed for the species with a male copulatory organ sclerotized, coiled, clockwise; ventral anchor with elongate superficial root, inconspicuous deep root; dorsal anchor with inconspicuous roots, and a constriction at the intersection between the shaft and the point. The host–parasite diversity scenario and host specificity of the species of Constrictoanchoratus n. gen. and Urocleidoides from the gills of H. malabaricus are also discussed in this study.

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Evapotranspiration seasonality across the Amazon basin

10.5194/esd-2016-75 ◽

2017 ◽

Author(s):

Eduardo Eiji Maeda ◽

Xuanlong Ma ◽

Fabien Wagner ◽

Hyungjun Kim ◽

Taikan Oki ◽

...

Keyword(s):

Amazon Basin ◽

Regional Climate ◽

Root Water Uptake ◽

Environmental Drivers ◽

Seasonal Patterns ◽

Wet Season ◽

Important Indicator ◽

Seasonally Dry ◽

Basin Scale ◽

Terrestrial Water

Abstract. Evapotranspiration (ET) of Amazon forests is a main driver of regional climate patterns and an important indicator of ecosystem functioning. Despite its importance, the seasonal variability of ET over Amazon forests, and its relationship with environmental drivers, is still poorly understood. In this study, we carry out a water balance approach to analyse seasonal patterns in ET and their relationships with water and energy drivers over five sub-basins across the Amazon basin. We used in-situ measurements of river discharge, and remotely sensed estimates of terrestrial water storage, rainfall, and solar radiation. We show that the characteristics of ET seasonality in all sub-basins differ in timing and magnitude. The highest mean annual ET was found in the northern Rio Negro basin (~ 1497 mm year−1) and the lowest values in the Solimões River basin (~ 986 mm year−1). For the first time in a basin-scale study, using observational data, we show that factors limiting ET vary across climatic gradients in the Amazon, confirming local-scale eddy covariance studies. Both annual mean and seasonality in ET are driven by a combination of energy and water availability, as neither rainfall nor radiation alone could explain patterns in ET. In southern basins, despite seasonal rainfall deficits, deep root water uptake allows increasing rates of ET during the dry season, when radiation is usually higher than in the wet season. We demonstrate contrasting ET seasonality with satellite greenness across Amazon forests, with strong asynchronous relationships in ever-wet watersheds, and positive correlations observed in seasonally dry watersheds. Finally, we compared our results with estimates obtained by two ET models, and we conclude that neither of the two tested models could provide a consistent representation of ET seasonal patterns across the Amazon.

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Energy balance measurements over a banana orchard in the Semiarid region in the Northeast of Brazil

Pesquisa Agropecuária Brasileira ◽

10.1590/s0100-204x2009001100001 ◽

2009 ◽

Vol 44 (11) ◽

pp. 1365-1373 ◽

Cited By ~ 2

Author(s):

Carlos Antonio Costa dos Santos ◽

Bernardo Barbosa da Silva ◽

Tantravahi Venkata Ramana Rao ◽

Christopher Michael Usher Neale

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Eddy Covariance ◽

Heat Fluxes ◽

Irrigation District ◽

Semiarid Region ◽

Energy Balance Closure ◽

Wet Season ◽

Growing Seasons ◽

Eddy Covariance System

The objective of this work was to evaluate the reliability of eddy covariance measurements, analyzing the energy balance components, evapotranspiration and energy balance closure in dry and wet growing seasons, in a banana orchard. The experiment was carried out at a farm located within the irrigation district of Quixeré, in the Lower Jaguaribe basin, in Ceará state, Brazil. An eddy covariance system was used to measure the turbulent flux. An automatic weather station was installed in a grass field to obtain the reference evapotranspiration (ET0) from the combined FAO-Penman-Monteith method. Wind speed and vapor pressure deficit are the most important variables on the evaporative process in both growing seasons. In the dry season, the heat fluxes have a similar order of magnitude, and during the wet season the latent heat flux is the largest. The eddy covariance system had acceptable reliability in measuring heat flux, with actual evapotranspiration results comparing well with those obtained by using the water balance method. The energy balance closure had good results for the study area, with mean values of 0.93 and 0.86 for the dry and wet growing seasons respectively.

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