Publications
Found 46 publication(s)
- of type
Cordova, M.; Orellana-Alvear, J.; Bendix, J.; Rollenbeck, R. & Celleri, R. (2024): Large-scale dynamics of extreme precipitation in the tropical Andes: combining weather radar observations and reanalysis data. Meteorology and Atmospheric Physics 136(4), 27.
Rollenbeck, R.; Orellana-Alvear, J.; Bendix, J.; Rodriguez, R.; Pucha-Cofrep, F.; Guallpa, M.; Fries, A. & Celleri, R. (2022): The Coastal El Niño Event of 2017 in Ecuador and Peru: A Weather Radar Analysis. Remote Sensing 14(4), 824.
Núñez, P.Á.; Silva, B.; Schulz, M.; Rollenbeck, R. & Bendix, J. (2021): Evapotranspiration estimates for two tropical mountain forest using high spatial resolution satellite data. International Journal of Remote Sensing 42(8), 2940--2962.
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DOI: 10.1080/01431161.2020.1864058
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Abstract:
Abstract:
Tropical Mountain Forest (TMF) provides important ecological functions like evapotranspiration (ET) that supplies moisture and energy to the atmosphere. ET observations are scarce and difficult to accomplish particularly in areas of high heterogeneity where TMF are. Remote sensing (RS) allows to quantify and to determine ET spatial variation at the landscape level. Detail imaginary improves high spatial variability retrieval. Thought the greater detail introduces cast shadows by trees which hamper image interpretation. The objective of this study is to characterize ET estimation for the TMF of the southern Ecuadorian Andes by combining meteorological data with high-resolution satellite images. Shadows from high resolution images were masked out by applying focal statistics. The analysis included two meteorological periods typical of the area; a wet period when rain prevails and a dry period when precipitation is more sporadic. The reference evapotranspiration (ET0) was calculated using the FAO-Penman Montheid method by applying data obtained from an automatic weather station. The enhanced vegetation index (EVI) was derived from 2 m resolution WorldView2 satellite images. Results showed a lower ET mean value during the wet period: 1.54 mm day−1 compared to 2.37 mm day−1. Two forest types, differentiated from its structural composition and topographical position (ravine and ridge), marked ET spatial variation. Ravine forest that has a more dense and closed canopy showed higher ET values for both meteorological conditions. A comparison between ET estimations and ET field measurements from a scintillometer device showed a good agreement (coefficient of correlation r = 0.89) that proves the validity of the method. This study demonstrates that the application of high spatial resolution improves ET estimation in TMF especially when shadows are removed. Also, emphasizes the importance of analysing spatial heterogeneity to properly assess ecosystem water flux terms.
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Keywords: |
remote sensing |
mountain rainforest |
Evapotranspiration |
Orellana-Alvear, J.; Celleri, R.; Rollenbeck, R.; Muñoz, P.; Contreras, P. & Bendix, J. (2020): Assessment of Native Radar Reflectivity and Radar Rainfall Estimates for Discharge Forecasting in Mountain Catchments with a Random Forest Model. Remote Sensing 12(12), 1.
Orellana-Alvear, J.; Celleri, R.; Rollenbeck, R. & Bendix, J. (2019): Optimization of X-Band Radar Rainfall Retrieval in the Southern Andes of Ecuador Using a Random Forest Model. Remote Sensing 11(14), 1632.
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DOI: 10.3390/rs11141632
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Abstract:
Abstract:
Despite many eorts of the radar community, quantitative precipitation estimation (QPE)
from weather radar data remains a challenging topic. The high resolution of X-band radar imagery
in space and time comes with an intricate correction process of reflectivity. The steep and high
mountain topography of the Andes enhances its complexity. This study aims to optimize the rainfall
derivation of the highest X-band radar in the world (4450 m a.s.l.) by using a random forest (RF)
model and single Plan Position Indicator (PPI) scans. The performance of the RFmodel was evaluated
in comparison with the traditional step-wise approach by using both, the Marshall-Palmer and a
site-specific Z–R relationship. Since rain gauge networks are frequently unevenly distributed and
hardly available at real time in mountain regions, bias adjustment was neglected. Results showed an
improvement in the step-wise approach by using the site-specific (instead of the Marshall-Palmer)
Z–R relationship. However, both models highly underestimate the rainfall rate (correlation coecient
< 0.69; slope up to 12). Contrary, the RF model greatly outperformed the step-wise approach in
all testing locations and on dierent rainfall events (correlation coecient up to 0.83; slope = 1.04).
The results are promising and unveil a dierent approach to overcome the high attenuation issues
inherent to X-band radars.
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Keywords: |
South Ecuador |
random forest |
radar |
calibration |
Cajas National Park |
Carrillo Rojas, G.; Silva, B.; Rollenbeck, R.; Celleri, R. & Bendix, J. (2018): The breathing of the Andean highlands: Net ecosystem exchange and evapotranspiration over the páramo of southern Ecuador. Agricultural and Forest Meteorology 265, 30-47.
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DOI: 10.1016/j.agrformet.2018.11.006
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Abstract:
Abstract:
Atmospheric carbon (CO2) exchange, evapotranspiration (ET) processes, and their interactions with climatic drivers across tropical alpine grasslands are poorly understood. This lack of understanding is particularly evident for the páramo, the highest vegetated frontier in the northern Andes, the main source of water for inter-Andean cities, and a large carbon storage area. Studies of CO2 and ET fluxes via the standard Eddy Covariance (EC) technique have never been applied to this region, limiting the understanding of diurnal / nocturnal exchanges and budget estimations. In this paper, we report the first EC analysis conducted on the Andean páramo (3765?m a.s.l.); this analysis measured CO2, ET, and micrometeorological variables over two years (2016–2018) to understand their interactions with climatic / biophysical controls. The páramo was found to be a source of CO2 and exhibited a net positive exchange (mean = +99?±?30 gC m?2 per year). The light-responses of net CO2 exchange and the primary productivity were correlated and model-parameterized. Evapotranspiration was 635?±?9?mm per year (51% of the annual rainfall total), and we obtained crop coefficients for the dominant vegetation (Tussock grass) based on reference-ET models FAO56 and ASCE-ERWI (0.90 and 0.78, respectively). We also compared our results to those from other high-altitude (alpine) and high-latitude grasslands (tundra). Finally, we demonstrate that our measurement period is representative of the páramo’s longer-term climate dynamics. Our investigation contributes to the body of knowledge on the land surface-atmosphere processes of the tropical Andes and supports decision-making about ecosystem services management and the preservation of this vulnerable biome.
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Keywords: |
Ecuador |
carbon |
Paramo |
Evapotranspiration |
Tropical Andes |
Eddy covariance |
Oñate-Valdivieso, F.; Fries, A.; Mendoza, K.; Gonzales-Jaramillo, V.; Pucha Cofrep, F.; Rollenbeck, R. & Bendix, J. (2017): Temporal and spatial analysis of precipitation patterns in an Andean region of southern Ecuador using LAWR weather radar. Meteorology and Atmospheric Physics 129(295), 1-12.
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DOI: 10.1007/s00703-017-0535-8
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Abstract:
Abstract:
This paper focuses on the analysis of precipitation patterns, using a Local Area Weather Radar to collect information about the precipitation distribution in an Andean region of southern Ecuador (cities of Loja, Zamora and Catamayo). 54 representative events were selected to develop daily precipitation maps and to obtain their relevant characteristics, which were related to the topography and the season. The results showed that a strong correlation between the areas covered by precipitation (RA coefficient) and the season exists. In general, humid air masses come from the east (Amazon Basin), but during the main rainy season (December to April), humidity also frequently enters the study region from the west (Pacific Ocean). The rainy season is characterized by convective precipitation, associated with higher evaporation rates during austral summer. The relatively dry season is formed between May and November, but considerable precipitation amounts are registered, too, due to advective moisture transport from the Amazon Basin, a result of the predominant tropical easterlies carrying the humidity up the eastern escarpment of the Andes, generally following the natural course of the drainage systems.
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Keywords: |
Ecuador |
precipitation |
radar |
Bendix, J.; Fries, A.; Zárate, J.; Trachte, K.; Rollenbeck, R.; Pucha Cofrep, F.; Paladines, R.; Palacios, I.; Orellana Alvear, J.; Oñate-Valdivieso, F.; Naranjo, C.; Mendoza, L.; Mejia, D.; Guallpa, M.; Gordillo, F.; Gonzales-Jaramillo, V.; Dobbermann, M.; Celleri, R.; Carrillo, C.; Araque, A. & Achilles, S. (2017): Radarnet Sur – first weather radar network in tropical high mountains. Bulletin of the American Meteorological Society 98(6), 1235-1254.
Rollenbeck, R.; Trachte, K. & Bendix, J. (2016): A New Class of Quality Controls for Micrometeorological Data in Complex Tropical Environments. Journal of Atmospheric and Oceanic Technology 33(1), 169-183.
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DOI: 10.1175/JTECH-D-15-0062.1
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Abstract:
Abstract:
Quality control is a particularly demanding problem for micrometeorological studies in complex environments. With the transition to electronic sensing and storage of climate data in high temporal resolution,
traditional approaches of homogenization are insufficient for addressing the small-scale variability and spatial
heterogeneity of the data. This problem can be successfully addressed by introducing a new class of control
procedures based on the physical and climatological relations between different climate variables. The new
approach utilizes knowledge about the interdependency of air temperature, precipitation, radiation, relative
air humidity, cloud cover, and visibility to develop empirical functions for determining the probability
margins for the co-occurrence of specific conditions in tropical mountains and deserts. It can also be applied to
other geographic settings by adjusting the parameters derived from the data itself. All procedures are integrated into a processing chain with feedback loops and combined with conventional logical and statistical
checks, which enables it to detect small errors that normally pass unnoticed. The algorithms are also adapted
to incorporate the short time steps of the original data to retain the potential for detailed process analyses.
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Keywords: |
climate |
microclimate |
Climate variability |
data quality |
Gonzalez, V.; Fries, A.; Rollenbeck, R.; Paladines, J.; Oñate-Valivieso, F. & Bendix, J. (2016): Assessment of deforestation during the last decades in Ecuador using NOAA-AVHRR satellite data. Erdkunde 70(No. 3), 217-235.
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DOI: 10.3112/erdkunde.2016.03.02
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Abstract:
Abstract:
Human activities during the last decades provoked a notable reduction in global forest cover. Knowing that
forest stands act as stock and sinks for carbon and other greenhouse gases, it is important to determine the existing forest
cover at country level and to calculate annual deforestation rates. This work uses NOAAsatellite images in a resolution of
1 km x 1 km to classify the surface of continental Ecuador in “forest” – “non-forest” pixels and to estimate the annual
deforestation rate from 1986 to 2001 as well as from 2001 to 2008. The method is based on a decision tree algorithm that
includes different spectral bands of the NOAA-AVHRRsensor and additional topographic and meteorological parameters.
The results show that the total forest cover of continental Ecuador was reduced from 48.1 % in 1986 to 36.8 % in 2008. The
calculated annual deforestation rates indicate that forest reduction increased during the last decade. The most affected area
is the Coastal Lowland, due to the enhanced population pressure, followed by the Amazon Basin, not only caused by the
governmental supported oil and mining industry, but also due to the uncontrolled timber extraction. The Andean Highland
has been less affected, because the major parts of this region were deforested before, during the Pre-Columbian-Era.
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Keywords: |
Ecuador |
NOAA-AVHRR |
remote sensing |
deforestation |
image pre-processing |
forest cover |
Makowski Giannoni, S.; Trachte, K.; Rollenbeck, R.; Lehnert, L.; Fuchs, J. & Bendix, J. (2016): Atmospheric salt deposition in a tropical mountain rainforest at the eastern Andean slopes of south Ecuador – Pacific or Atlantic origin?. Atmospheric chemistry and physics 16, 10241-10261.
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DOI: 10.5194/acp-16-10241-2016
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Abstract:
Abstract:
Sea salt (NaCl) has recently been proven to be of the utmost importance for ecosystem functioning in Amazon lowland forests because of its impact on herbivory, litter decomposition and, thus, carbon cycling. Sea salt deposition should generally decline as distance from its marine source increases. For the Amazon, a negative east–west gradient of sea salt availability is assumed as a consequence of the barrier effect of the Andes Mountains for Pacific air masses. However, this generalized pattern may not hold for the tropical mountain rainforest in the Andes of southern Ecuador. To analyse sea salt availability, we investigated the deposition of sodium (Na+) and chloride (Cl?), which are good proxies of sea spray aerosol. Because of the complexity of the terrain and related cloud and rain formation processes, sea salt deposition was analysed from both, rain and occult precipitation (OP) along an altitudinal gradient over a period between 2004 and 2009. To assess the influence of easterly and westerly air masses on the deposition of sodium and chloride over southern Ecuador, sea salt aerosol concentration data from the Monitoring Atmospheric Composition and Climate (MACC) reanalysis data set and back-trajectory statistical methods were combined. Our results, based on deposition time series, show a clear difference in the temporal variation of sodium and chloride concentration and Na+???Cl? ratio in relation to height and exposure to winds. At higher elevations, sodium and chloride present a higher seasonality and the Na+???Cl? ratio is closer to that of sea salt. Medium- to long-range sea salt transport exhibited a similar seasonality, which shows the link between our measurements at high elevations and the sea salt synoptic transport. Although the influence of the easterlies was predominant regarding the atmospheric circulation, the statistical analysis of trajectories and hybrid receptor models revealed a stronger impact of the north equatorial Atlantic, Caribbean, and Pacific sea salt sources on the atmospheric sea salt concentration in southern Ecuador. The highest concentration in rain and cloud water was found between September and February when air masses originated from the north equatorial Atlantic, the Caribbean Sea and the equatorial Pacific. Together, these sources accounted for around 82.4?% of the sea salt budget over southern Ecuador.
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Keywords: |
chloride |
sodium |
rain |
Nutrient deposition |
Occult precipitation |
transport modelling |
Back trajectories |
Peters, T.; Drobnik, T.; Meyer, H.; Rankl, M.; Richter, M.; Rollenbeck, R.; Thies, B. & Bendix, J. (2014): Environmental Changes Affecting the Andes of Ecuador. In: Bendix, J., Beck, E., Bräuning, A., Makeschin, F., Mosandl, R., Scheu, S., Wilcke, W. (eds.): Ecosystem Services, Biodiversity and Environmental Change in a Tropical Mountain Ecosystem of South ( ), Springer.
Wagemann, J.; Thies, B.; Rollenbeck, R.; Peters, T. & Bendix, J. (2015): Regionalization of wind-speed data to analyse tree-line wind conditions in the eastern Andes of southern Ecuador. Erdkunde 69, 3-19.
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DOI: 10.3112/erdkunde.2015.01.01
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Abstract:
Abstract:
This paper presents a method to extrapolate wind-speed data and to calculate wind-speed and dynamic pressure maps for the complex topography of a mountain rainforest area in the tropical Andes of southeastern Ecuador. The spatial differentiation of dynamic wind pressure in this area is claimed to be a major determinant of the altitude of the tree-line ecotone and to affect the tree line’s physiognomy. The paper presents a hybrid method encompassing statistical data analysis using the Weibull distribution and a digital terrain analysis, taking topographical shelter effects into account. The method is used to derive mean and maximum wind-speed and dynamic pressure maps to reveal whether the tree-line ecotone is influenced by direct wind effects. On average, the tree-line ecotone on the eastern slopes shows a clear average depression of ~50 m. These slopes are affected by higher dynamic wind stress, so have a more disturbed canopy. These altered vegetation structures may be caused mainly by direct wind effects and to a smaller extent by indirect effects, such as high humidity.
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Keywords: |
wind speed |
regionalization |
Makowski, S.; Rollenbeck, R.; Trachte, K. & Bendix, J. (2014): Natural or anthropogenic? On the origin of atmospheric sulfate deposition in the Andes of southeastern Ecuador. Atmos. Chem. Phys 14, 11297–11312.
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DOI: 10.5194/acp-14-11297-2014
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Abstract:
Abstract:
Atmospheric sulfur deposition above certain limits
can represent a threat to tropical forests, causing nutrient
imbalances and mobilizing toxic elements that impact biodiversity
and forest productivity. Atmospheric sources of sulfur
deposited by precipitation have been roughly identified in
only a few lowland tropical forests. Even scarcer are studies
of this type in tropical mountain forests, many of them megadiversity
hotspots and especially vulnerable to acidic deposition.
In these places, the topographic complexity and related
streamflow conditions affect the origin, type, and intensity of
deposition. Furthermore, in regions with a variety of natural
and anthropogenic sulfur sources, like active volcanoes and
biomass burning, no source emission data has been used for
determining the contribution of each source to the deposition.
The main goal of the current study is to evaluate sulfate
(SO?
4 ) deposition by rain and occult precipitation at two topographic
locations in a tropical mountain forest of southern
Ecuador, and to trace back the deposition to possible emission
sources applying back-trajectory modeling. To link upwind
natural (volcanic) and anthropogenic (urban/industrial
and biomass-burning) sulfur emissions and observed sulfate
deposition, we employed state-of-the-art inventory and satellite
data, including volcanic passive degassing as well. We
conclude that biomass-burning sources generally dominate
sulfate deposition at the evaluated sites. Minor sulfate transport
occurs during the shifting of the predominant winds
to the north and west. Occult precipitation sulfate deposition
and likely rain sulfate deposition are mainly linked to
biomass-burning emissions from the Amazon lowlands. Volcanic
and anthropogenic emissions from the north and west
contribute to occult precipitation sulfate deposition at the
mountain crest Cerro del Consuelo meteorological Station and to rain-deposited sulfate at the upriver mountain pass El
Tiro meteorological station.
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Keywords: |
Nutrient deposition |
Silva, B.; Roos, K.; Fries, A.; Rollenbeck, R.; Beck, E. & Bendix, J. (2014): Mapping Two Competing Grassland Species from a Low-Altitude Helium Balloon. IEEE Journal of selected topics in applied earth observations and remote sensing 7(7), 3038 - 3049.
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DOI: 10.1109/JSTARS.2014.2321896
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Abstract:
Abstract:
This paper describes a method of low-altitude remote
sensing in combination with in situ measurements (leaf area, spectroscopy, and position) to monitor the postfire canopy recovery of two competing grassland species. The method was developed in the Andes of Ecuador, where a tethered balloon with a digital camera was deployed to record a time series of very high spatial resolution
imagery ( nominal resolution = 2cm ) of an experimental plot covered by two competing species: 1) the pasture grass, Setaria sphacelata; and 2) the invasive southern bracken, Pteridium arachnoideum. Image processing techniques were combined to solve geometric issues and construct high-quality mosaics for image classification. The semiautomatic and object-oriented classification method was based on geometrical and textural attributes of image segments and showed promising results for detecting the invasive bracken fern in Setaria pastures (performance by area under the curve, AUC = 0.88). Valuable insights are given into vegetation monitoring applications using unmanned aerial vehicles, which produces a time series of species-specific maps, including foliage projective cover (FPC) and leaf area index (LAI). This new method constitutes an important and accessible tool for ecological investigations of competing species in pastures and validation of remote sensing information on mountain environments.
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Keywords: |
bracken |
pasture |
land cover |
LAI |
remote sensing |
abandoned pasture |
burning |
Bracken fern |
Fries, A.; Rollenbeck, R.; Bayer, F.; Gonzalez, V.; Oñate-Valivieso, F.; Peters, T. & Bendix, J. (2014): Catchment precipitation processes in the San Francisco valley in southern Ecuador: combined approach using high-resolution radar images and in situ observations. Meteorology and Atmospheric Physics 703, x.
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DOI: 10.1007/s00703-014-0335-3
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Abstract:
Abstract:
The precise estimation of precipitation quantities in tropical mountain regions is in great demand by ecological and hydrological studies, due to the heterogeneity of the rainfall distribution and the lack of meteorological station data. This study uses radar images and ground station data to provide the required high-resolution precipitation maps. Also wind data are taken into account, due to its influence on the precipitation formation and to demonstrate the relation between synoptic wind, topography and the precipitation distribution inside small mountain valleys. The study analyses the rainfall distribution and amounts of 4 days inside the San Francisco Valley, a small catchment in the tropical Andes of southern Ecuador, representing different seasons and the typical atmospheric flows, which are correlated to the annual precipitation map. The results show that the rainfall distribution and amounts are generally defined by the wind direction and velocity, besides the topographic location in relation to the main barriers and pathways. The dominant wind direction causes a division of the catchment in a wetter eastern and a dryer western part. Moreover, the annual seasons are reversed; the main rainy season for the eastern part occurs between June and August, while the western part reaches the precipitation maximum between January and March. This may have influence on the species composition at the different slopes and the annual hydrological cycle inside the catchment.
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Keywords: |
Atmospheric Sciences |
Meteorology |
Terrestrial Pollution |
Waste Water Technology |
Water Pollution Control |
Water Management |
Aquatic Pollution |
Wilcke, W.; Leimer, S.; Peters, T.; Emck, P.; Rollenbeck, R.; Trachte, K.; Valarezo, C. & Bendix, J. (2013): The nitrogen cycle of tropical montane forest in Ecuador turns inorganic under environmental change. Global Biogeochemical Cycles 27(4), 1194-1204.
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DOI: 10.1002/2012GB004471
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Abstract:
Abstract:
Water-bound nitrogen (N) cycling in temperate terrestrial ecosystems of the Northern
Hemisphere is today mainly inorganic because of anthropogenic release of reactive N to
the environment. In little-industrialized and remote areas, in contrast, a larger part of
N cycling occurs as dissolved organic N (DON). In a north Andean tropical montane forest
in Ecuador, the N cycle changed markedly during 1998–2010 along with increasing
N deposition and reduced soil moisture. The DON concentrations and the fractional
contribution of DON to total N significantly decreased in rainfall, throughfall, and soil
solutions. This inorganic turn of the N cycle was most pronounced in rainfall and became
weaker along the flow path of water through the system until it disappeared in stream water.
Decreasing organic contributions to N cycling were caused not only by increasing inorganic
N input but also by reduced DON production and/or enhanced DON decomposition.
Accelerated DON decomposition might be attributable to less waterlogging and higher
nutrient availability. Significantly increasing NO3-N concentrations and NO3-N/NH4-N
concentration ratios in throughfall and litter leachate below the thick organic layers indicated
increasing nitrification. In mineral soil solutions, in contrast, NH4-N concentrations increased and NO3-N/NH4-N concentration ratios decreased significantly, suggesting increasing net ammonification. Our results demonstrate that the remote tropical montane forests on the rim of the Amazon basin experienced a pronounced change of the N cycle in only one decade. This change likely parallels a similar change which followed industrialization in the temperate zone of the Northern Hemisphere more than a century ago.
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Keywords: |
climate change |
nitrification |
N deposition |
terrestrial N cycling |
dissolved organic N |
Makowski, S.; Rollenbeck, R.; Fabian, P. & Bendix, J. (2013): Complex topography influences atmospheric nitrate deposition in a neotropical mountain rainforest. Atmospheric environment 79, 385-394.
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DOI: 10.1016/j.atmosenv.2013.06.023
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Abstract:
Abstract:
Future increase of atmospheric nitrogen deposition in tropical regions is expected to have negative impacts on forests ecosystems and related biogeochemical processes. In tropical mountain forests topography causes complex streamflow and rainfall patterns, governing the atmospheric transport of
pollutants and the intensity and spatial variability of deposition. The main goal of the current study is to link spatio-temporal patterns of upwind nitrogen emissions and nitrate deposition in the San Francisco Valley (eastern Andes of southern Ecuador) at different altitudinal levels. The work is based on Scanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) retrieved-NO2 concentrations, NOx biomass burning emissions from the Global Fire Emissions Database (GFEDv3), and regional vehicle emissions inventory (SA-INV) for urban emissions in South America. The emission data is used as input for lagrangian atmospheric backward trajectory modeling (FLEXTRA) to model the transport to the study area. The results show that NO3 À concentrations in occult precipitation samples are significantly correlated to long-range atmospheric secondary nitrogen transport at the highest meteorological stations (MSs) only, whereas for NO3 À concentrations in rain samples this correlation is more pronounced at the lower MSs. We conclude that ion concentrations in occult precipitation at the uppermost MSs are mainly linked to distant emission sources via the synoptic circulation impinging the more exposed higher sites. Lower correlations close to the valley bottom are due to a lower occult precipitation frequency and point to a contamination of the samples by local pollution sources not captured by the used emission data sources.
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Keywords: |
wet deposition |
nitrogen |
nitrate |
Southern Ecuador |
Silva, B.; Roos, K.; Voss, I.; König, N.; Rollenbeck, R.; Scheibe, R.; Beck, E. & Bendix, J. (2012): Simulating canopy photosynthesis for two competing species of an anthropogenic grassland community in the Andes of southern Ecuador. Ecological Modelling 239, 14-26.
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DOI: 10.1016/j.ecolmodel.2012.01.016
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Abstract:
Abstract:
Tropical mountain forest in the Andes of southeastern Ecuador is regularly destroyed to gain pasture land by cultivating the C4 grass Setaria sphacelata. After recurrent burning of the pastures, the grass is partly outcompeted by the C3 southern bracken (Pteridium arachnoideum). This competition represents the problematic of pasture degradation and increasing deforestation, due to the necessity of new pasture land. Because no information on the growth potential of both species in the Andes of Ecuador is available, a growth simulation model has been improved and properly parameterized with field observations. The measured speciesand site-specific physiological and edaphic parameters are presented in this paper, as well as the model validation with field observations of leaf CO2 assimilation. The validation showed deviations of simulated from observed leaf net assimilation lower than 5% of the observed values. The validated model was run with a fully realistic meteorological forcing of the year 2008 (10 min time step). The main result points to slightly higher growth potential of Setaria with 5879 g m-2 a-1, based on an annual CO2 net assimilation rate of 217 mol CO2m-2 a-1. The calculated growth potential of bracken was 5554 g m-2 a-1, based on the CO2 net assimilation of 197 mol CO2m-2 a-1. In addition, it was shown that decreasing incoming solar radiation and low temperature are favourable weather conditions for bracken in contrary to the pasture grass Setaria.
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Keywords: |
Ecuador |
Setaria sphacelata |
simulation |
photosynthesis |
parameters estimation |
realistic forcing |
southern bracken |
Fries, A.; Rollenbeck, R.; Nauss, T.; Peters, T. & Bendix, J. (2012): Near surface air humidity in a megadiverse Andean mountain ecosystem of southern Ecuador and its regionalization.. Agricultural and Forest Meteorology 152, 17-30.
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DOI: 10.1016/j.agrformet.2011.08.004
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Abstract:
Abstract:
The near surface humidity in a megadiverse mountain ecosystem in southern Ecuador is examined on the basis of Relative Humidity (RH) measurements inside the natural mountain forest and at open sites along an altitudinal gradient from 1700 to 3200 m. The main methodological aim of the current study is to generate a humidity regionalization tool to provide spatial datasets on average monthly mean, minimum and maximum RH, Specific Humidity (q) and Specific Saturation Deficit (DS) by using observation data of RH. The maps based on data of the period 1999–2009 are needed by ecological projects working on various plots where no climate station data are available. The humidity maps are generated by combining a straightforward detrending technique with a Digital Elevation Model and a satellite-based land cover classification which also provides the relative forest cover per pixel. The topical aim of the study is to investigate the humidity distribution and structure of both manifestations of our ecosystem (pastures and natural vegetation) with special considerations to the ecosystem regulation service by converting natural forest into pasture. The results reveal a clear differentiation over the year, partly triggered by the change of synoptic weather situation but also by land cover effects. Humidity amplitudes are particularly low during the main rainy season when cloudiness and rainfall are high, but markedly pronounced in the relative dry season when daily irradiance and outgoing nocturnal radiation causes distinct differences between the land cover units. Particularly the upper pasture areas gained by slash and burn of the natural forest exhibit the lowest humidity values while the humidity inside the mountain forest is significantly higher due to the regulating effects of the dense vegetation. Thus, clearing the forest clearly reduces the regulation function (regulating ecosystem services) of the ecosystem which might become problematic for reforestation under future global warming.
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Keywords: |
South Ecuador |
regionalization |
forest and open land |
distribution |
structure |
near surface humidity |
Bendix, J.; Trachte, K.; Palacios, E.W.; Rollenbeck, R.; Göttlicher, D.; Nauss, T. & Bendix, A. (2011): El Niño meets La Niña - anomalous rainfall patterns in the "traditional" El Niño region of southern Ecuador . Erdkunde 65, 151-167.
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DOI: 10.3112/erdkunde.2011.02.04
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Abstract:
Abstract:
In this paper, the central Pacific cold event of 2008 and its exceptionally warm conditions in the eastern tropical
Pacific are analyzed by using rainfall data of south Ecuadorian meteorological stations, sea surface temperatures in the El
Niño3 and 1+2 regions, and simulations with the Weather Research and Forecasting (WRF) model. It can be shown that El
Niño-like rainfall conditions with severe inundations occur particularly in the coastal plains of southern Ecuador while a
central Pacific cold event prevails. In contrary to previous situations, positive rainfall anomalies as a result of El Niño-like
conditions in the El Niño1+2 region during the 2008 La Niña event occurred in both regions, the coastal plains and the
highlands, for the first time. A detailed analysis of the ocean-atmosphere system during episodes of heavy rainfall reveals
typical El Niño circulation and rainfall patterns as observed during previous El Niño events for the coastal area and La
Niña-like conditions for the highlands. The spreading of Pacific instability in the Niño1+2 region to the eastern escarpment
of the Andes could be the result of a temporary eastward shift of the Walker circulation. The unusual combination of El
Niño-like conditions in the eastern tropical Pacific during a La Niña state in the central Pacific is the newest indicator for
an impact mode shift regarding severe rainfall anomalies during El Niño/La Niña events in the traditional El Niño area
of southern Ecuador since the end of the last century. Since 2000, El Niño events unexpectedly provide below average
rainfall while central Pacific La Niña conditions generate exceptional severe flooding in the normally drier coastal plains.
The novel sea surface temperature (SST) anomaly dipole structure between the eastern and central/western tropical Pacific
and the weakening of El Niño events since 2000 could be due to natural decadal oscillations in the El Niño background
state, the Pacific Decadal Oscillation (PDO). However, the observed atmospheric patterns and the recent increase of the
SST anomaly difference between the central and the eastern tropical Pacific resemble structures that also result from climate
change simulations.
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Keywords: |
South Ecuador |
el nino |
la nina |
ENSO |
rainfall anomalies |
sea surface temperature anomalies |
Trachte, K.; Rollenbeck, R. & Bendix, J. (2010): Nocturnal convective cloud formation under clear‐sky conditions at the eastern Andes of south Ecuador. Journal of Geophysical Research 115, D24203.
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DOI: 10.1029/2010JD014146
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Abstract:
Abstract:
The formation of nocturnal convective clouds at the eastern Andes of south Ecuador and the adjacent Peruvian Amazon basin was investigated in a numerical model study. Their formation is expected to be an interactive procedure of nocturnal downslope flows in
the Andean terrain, which forms a concave drainage system in the target area. Satellite imagery were used for both the identification of a sample case with a nocturnal cold cloud appearance and for the verification of the simulated results. The cloud patterns were
distinguished on the basis of IR temperatures. A comparison of the data demonstrated the occurrence of a cold cloud shield in the target area, although the modeled cluster is significantly smaller. Further analysis of the development of the convective cells confirmed the assumed underlying processes. A strong current in the lower atmosphere, presumably a drainage flow, was recognizable in association with strong moisture convergence using a cross section through the cluster. Their presence was confirmed on the basis of their characteristic features and the surface energy fluxes as the driving force for thermally induced downslope flows.
Rollenbeck, R.; Bendix, J. & Fabian, P. (2011): Spatial and temporal dynamics of atmospheric water inputs in tropical mountain forests of South Ecuador. . Hydrological Processes 25, 344 - 352.
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DOI: 10.1002/hyp.7799
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Abstract:
Abstract:
As part of an interdisciplinary research programme, the spatial and temporal variability of precipitation in southern Ecuador
has been investigated since January 2002. The study site is located at the northern margin of the Podocarpus National Park in
the vicinity of Loja, about 500 km south of Quito, at altitudes ranging from 1800 to 3200 m.a.s.l. Due to its low density, the
conventional rainfall station network fails to register the highly variable spatial distribution of rain, whereas contributions by
fog are not accounted at all. Hence, for the first time in a tropical montane forest setting, a weather radar was used, covering a
radius of 60 km and reaching from the Amazon Basin to the coastal plains of the region. Furthermore, a network of sampling
stations supplies data about the altitudinal gradient of fog and rainwater inputs. The precipitation distribution in the study
area proves to be far more variable than previously thought and is strongly coupled to the orographic characteristics and
the special topographical setting of the landscape. Maxima in precipitation occur especially in the eastern parts of the radar
range on slopes exposed to advected moisture from the Amazon Basin, whereas the highest crests of the Andes receive less
precipitation. The study area has two cloud condensation levels, occurring at 1500?2000 and 2500?3500 m.a.s.l., respectively.
At 1800?2000 m.a.s.l., fog is estimated to contribute an additional input of 5% of conventionally measured rainfall, increasing
to about 35% at the highest measurement station (3200 m.a.s.l.). In contrast to some other tropical mountains, there seems to be
no maximum zone of water input, although the gradient remains positive up to the highest altitudes. The unusual precipitation
distribution is thought to reflect the contrasting climatological influences operating in the study area.
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Keywords: |
tropical montane forest |
rain |
fog |
radar |
Rollenbeck, R.; Fabian, P. & Bendix, J. (2010): Spatial and temporal dynamics of atmospheric water- and nutrient inputs in tropical mountain forests of southern Ecuador. . In: L. A. Bruijnzeel, F. N. Scatena,; L. S. Hamilton (eds.): Tropical Montane Cloud Forests: Science for Conservation and Management ( ), Cambridge University Press, Cambridge, 367- 377.
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Abstract:
Abstract:
As part of an interdisciplinary research program, the
spatial and temporal variability of precipitation and
associated nutrient inputs in southern Ecuador have
been investigated since January 2002. The study site
is located at the northern margin of the Podocarpus
National Park in the vicinity of Loja, about 500 km
south of Quito, at altitudes ranging from 1800 to 3180
m.a.s.l. Due to its low density, the conventional rainfall
station network fails to register the highly variable
distribution of rain whereas fog is not accounted for
at all. Hence, a new measurement infrastructure had
to be installed. For the first time in a tropical montane
forest setting, a Weather Radar was used, covering a
radius of 60 km and reaching from the Amazon Basin
to the coastal plains of the region. Furthermore, a dense
network of sampling stations provided data about the
altitudinal gradient of fog water inputs and the
chemical properties of the different precipitation
types. This combined approach provided important
information on the formative processes of rain events
on the eastern escarpment of the Andes. Rainfall
distribution proved far more variable than previously
known and strongly coupled to the orographic
characteristics of the landscape. Maxima occurred
especially on the exposed mountain slopes in the
eastern parts of the Radar range, whereas the highest
crests of the Andes received less precipitation. The
study area has two cloud condensation levels, occurring
at 1500?2000 m and 2500?3500 m.a.s.l., respectively. Fog was estimated to provide an additional 5?35%
of water to conventionally measured rainfall. As with
rainfall, fog capture exhibited a marked altitudinal
gradient. Precipitation samples were analyzed for their
main chemical properties to calculate spatial gradients
as well as temporal trends of nutrient inputs. Although
average matter fluxes were fairly low, episodic events
contributed relevant amounts to the overall ecosystem
nutrient budget.
Rollenbeck, R. & Bendix, J. (2011): Rainfall distribution in the Andes of southern Ecuador derived from blending weather radar data and meteorological field observations. . Atmos. Res. 99, 277?289.
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DOI: 10.1016/j.atmosres.2010.10.018
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Abstract:
Abstract:
The Andes of Ecuador show an extreme heterogeneity of spatial and temporal distribution of precipitation. The existing operational network of the national weather service is not capable of reproducing these complex patterns. By using a cost-efficient rain radar and a network of high-resolution rain gauges, the real complexity of the rainfall distribution and the meteorological processes of rainfall formation can be assessed. A blendingmethod encompassing geostatistical
tools allows to derive a comprehensive rainfall climatology for the study area. Precipitation is predominantly of the advective type, associated with humid air masses from the Amazon basin transported by the tropical easterlies. The typical form is light to heavy drizzle with long duration but lower rain rates. However, in contrast to former knowledge there is no single mechanism of rain formation for any given place. Several processes interact like small and large-scale convective cloud systems, local and regional valley/mountain breeze systems and terrain-lines of preferred moisture transport interact on various time scale. This leads to complex patterns of rainfall in space and
time. Several types of characteristic weather situations are revealed by the study. They are characterized by specific combinations of local and regional atmospheric processes and interactions with the topographical configuration. They are modified by mesoscale and continental circulation patterns as the annual shift of pressure cells, the east Andean low-level Jet and katabatic flows.
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Keywords: |
precipitation |
Andes |
radar |
calibration |
climatology |
Roos, K.; Rollenbeck, R.; Peters, T.; Bendix, J. & Beck, E. (2010): Growth of Tropical Bracken (Pteridium arachnoideum): Response to Weather Variations and Burning. Invasive Plant Science and Management 3, 402-411.
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DOI: 10.1614/IPSM-D-09-00031.1
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Abstract:
Abstract:
The ecology of tropical bracken, which occurs in tropical regions, is not well known. We studied its response to weather variations and burning in the south Ecuadorian Andes, where this weed had already overgrown 40% of the pastureland. In field observations, a constant 1:1 ratio of emerging and dying leaves suggested limitation of frond density by nutrient shortage. Short-term deviations from that ratio could be related to weather variations. Spells of dry weather temporarily increased mortality but stimulated emergence of new fronds. Lifespan of the fronds produced immediately after a fire was longer than of those produced during unaffected bracken growth. A burst of frond development during the initial 2 to 3 mo was observed after a fire followed by self-thinning to a stable level. To analyze the effect of fire on bracken, rhizomes were treated with heat pulses. Rhizomes were heat tolerant up to 70 C, and frond production from short shoots was enhanced by elevated temperature. Burning apparently releases apical dominance of developed fronds, as does cutting, and stimulates bud break. The local practice of pasture maintenance in Ecuador of repeated burning favors growth of the fern.
Fries, A.; Rollenbeck, R.; Göttlicher, D.; Nauss, T.; Homeier, J.; Peters, T. & Bendix, J. (2009): Thermal structure of a megadiverse Andean mountain ecosystem in southern Ecuador and its regionalization. Erdkunde 63, 321-335.
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DOI: 10.3112/erdkunde.2009.04.03
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Abstract:
Abstract:
The thermal structure of a megadiverse mountain ecosystem in southern Ecuador is examined on the basis of temperature measurements inside the natural mountain forest and at open-sites along an altitudinal gradient from 1600 to 3200 m. The main methodological aim of the current study is to develop an air temperature regionalization tool to provide spatial datasets on average monthly mean, minimum and maximum temperature by using observation data. The maps, based on data of the period 1999?2007, are needed by ecological projects working on various plots where no climate station data are available. The temperature maps are generated by combining a straightforward detrending technique with a Digital Elevation Model and a satellite-based land cover classification which also provides the relative forest cover per pixel. The topical aim of the study is to investigate the thermal structure of both manifestations of our ecosystem (pastures and natural vegetation) with special considerations to the ecosystem temperature regulation service by converting natural forest into pasture. The results reveal a clear thermal differentiation over the year, partly triggered by the change of synoptic weather situation but also by land cover effects. Thermal amplitudes are particularly low during the main rainy season when cloudiness and air humidity are high, but markedly pronounced in the relative dry season when daily irradiance and outgoing nocturnal radiation cause distinct differences between the land cover units. Particularly the lower pasture areas gained by slash and burn of the natural forest exhibit the most extreme thermal conditions while the atmosphere inside the mountain forest is slightly cooler due to the regulating effects of the dense vegetation. Thus, clearing the forest clearly reduces the thermal regulation function (regulating ecosystem services) of the ecosystem which might become problematic under future global warming.
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Keywords: |
air temperature |
South Ecuador |
thermal structure |
regionalization |
forest and open land |
Bendix, J.; Silva, B.; Roos, K.; Göttlicher, D.; Rollenbeck, R.; Nauss, T. & Beck, E. (2009): Model parameterization to simulate and compare the PAR absorption potential of two competing plant species. International Journal of Biometeorology OnlineFirs, xx-xx.
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DOI: 10.1007/s00484-009-0279-3
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Abstract:
Abstract:
Abstract Mountain pastures dominated by the pasture grass Setaria sphacelata in the Andes
of southern Ecuador are heavily infested by southern bracken (Pteridium arachnoideum), a major
problem for pasture management. Field observations suggest that bracken might outcompete the grass
due to its competitive strength with regard to the absorption of photosynthetically active radiation
(PAR). To understand the PAR absorption potential of both species, the main aim of the current paper
is to (i) parameterize a radiation scheme of a two-big leaf model by deriving structural (LAI, leaf angle
parameter) and optical(leaf albedo, transmittance) plant traits for average individuals from field
surveys, (ii) to initialise the properly parameterized radiation scheme with realistic global irradiation
conditions of the Rio San Francisco Valley in the Andes of southern Ecuador, and (iii) to compare the
PAR absorption capabilities of both species under typical local weather conditions. Field data show
that bracken reveals a slightly higher average leaf area index (LAI) and more horizontally oriented
leaves in comparison to Setaria. Spectrometer measurements reveal that bracken and Setaria are
characterised by a similar average leaf absorptance. Simulations with the average diurnal course of
incoming solar radiation (1998-2005) and the mean leaf-sun geometry reveal that PAR absorption is
fairly equal for both species. However, the comparison of typical clear and overcast days show that two
parameters, (i) the relation of incoming diffuse and direct irradiance, and (ii) the leaf-sun geometry
play a major role for PAR absorption in the two-big leaf approach: Under cloudy sky conditions (mainly
diffuse irradiance), PAR absorption is slightly higher for Setaria while under clear sky conditions
(mainly direct irradiance), the average bracken individual is characterized by a higher PAR absorption
potential. (~74 MJ m-2 a-1) . The latter situation which occurs if the maximum daily irradiance exceeds
615 W m-2 is mainly due to the nearly orthogonal incidence of the direct solar beam onto the
horizontally oriented frond area which implies a high amount of direct PAR absorption during the
noon maximum of direct irradiance. Such situations of solar irradiance favouring a higher PAR
absorptance of bracken occur in ~36% of the observation period (1998-2005). By considering the
annual course of PAR irradiance in the San Francisco Valley, the clear advantage of bracken on clear
days (36% of all days) is completely compensated by the slight but more frequent advantage of Setaria
under overcast conditions (64% of all days). This means that neither bracken nor Setaria show a
distinct advantage in PAR absorption capability under the current climatic conditions of the study area.
Homeier, J.; Breckle, S.W.; Günter, S.; Rollenbeck, R. & Leuschner, C. (2009): Tree diversity, forest structure and productivity along altitudinal and topographical gradients in a species-rich Ecuadorian montane rainforest. Biotropica 42(2), 140-148.
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DOI: 10.1111/j.1744-7429.2009.00547.x
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Abstract:
Abstract:
We studied the spatial heterogeneity of tree diversity, and of forest structure and productivity in a highly diverse tropical mountain area in southern Ecuador with the aim of understanding the causes of the large variation in these parameters. Two major environmental gradients, elevation and topography, representing a broad range of climatic and edaphic site conditions, were analyzed. We found the highest species richness of trees in valleys <2100 m. Valleys showed highest values of basal area, leaf area index and tree basal area increment as well. Tree diversity also increased from ridges to valleys, while canopy openness decreased. Significant relationships existed between tree diversity and soil parameters (pH, total contents of Mg, K, Ca, N and P), and between diversity and the spatial variability of pH and Ca and Mg contents suggesting a dependence of tree diversity on both absolute levels and on the small-scale heterogeneity of soil nutrient availability. Tree diversity and basal area increment were positively correlated, partly because both are similarly affected by soil conditions. We conclude that the extraordinarily high tree species richness in the area is primarily caused by three factors: (1) the existence of steep altitudinal and topographic gradients in a rather limited area creating a small-scale mosaic of edaphically different habitats; (2) the intermingling of Amazonian lowland plant species, that reach their upper distribution limits, and of montane forest species; and (3) the geographical position of the study area between the humid eastern Andean slope and the dry interandean forests of South Ecuador.
Rollenbeck, R.; Fabian, P. & Bendix, J. (2008): Temporal Heterogeneities - Matter Deposition from Remote Areas. In: Beck, Erwin; Bendix, Jörg; Kottke, Ingrid; Makeschin, Franz; Mosandl, Reinhard (eds.): Gradients in a Tropical Mountain Ecosystem of Ecuador (Ecological Studies 198), Springer, Berlin Heidelberg, 303-310.