Browsing by Author "Frede, Hans Georg"

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Identifcation of the runoff generation processes in a montane cloud forest combining hydrometric data and mixing model analysis
(Universidad de Cuenca, 2011-07) Crespo Sánchez, Patricio Javier; Bücker, Amelie; Feyen, Jan; Vache, Kellie B.; Frede, Hans Georg; Universidad de Cuenca; Dirección de Investigación de la Universidad de Cuenca; Breuer, Lutz
Field observations of runoff generation in pristine montane cloud forests are scarce. However, this knowledge is important for a sustainable natural resources management. Here we report results of a study carried out in the San Francisco River basin (75,3 km2) located on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The basin is mainly covered with cloud forest, sub-páramo, pasture and ferns. A nested sampling approach was used for the collection of stream water samples and discharge measurements in the main tributaries and outlet of the basin. Additionally, soil and rock water samples were collected. Weekly to biweekly water grab samples were taken at all stations in the period April 2007 to November 2008. Hydrometric, mean residence time and mixing model approaches allowed identifying the main hydrological processes that control the runoff generation in the basin. Results clearly reveal that flow during dry conditions mainly consists of lateral flow through the C-horizon and cracks in the top weathered bedrock layer. The data shows that all catchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favor water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral sub-surface flow contributes most to streamflow. Under wet conditions in forested catchments streamflow is controlled by near-surface lateral flow through the organic horizon, and it is unlikely that Horton overland flow occurs during storm events. By absence of the litter layer in pasture streamflow under wet conditions primarily originates from the rooted surface layers and the A horizon, and Hortonian overland flow during extreme events.
Identifying controls of the rainfall-runoff response of small catchments in the tropical Andes (Ecuador)
(2011-07-24) Crespo, Patricio; Feyen, Jan; Buytaert, Wouter; Bücker, Amelie; Breuer, Lutz; Frede, Hans Georg; Ramírez, Marco
Tropical mountain regions are characterized by strong spatial climate gradients which together with the limited amount of data and knowledge of the underlying processes hinder the management of the water resources. Especially for regional-scale prediction it is important to identify the dominant factors controlling the rainfall–runoff response and link those to known spatial patterns of climate, soils, and vegetation. This study analyzes the rainfall–runoff relation of 13 intensively monitored micro-catchments in the Andes of southern Ecuador. The results of this study show that streamflow in the southern cordillera of the Ecuadorian Andes, above 2500 m a.s.l., primarily consists of subsurface flow. The yearly amount of streamflow is controlled by the annual rainfall depth, whereas the temporal distribution is mainly governed by the lateral saturated hydraulic conductivity, the soil water retention and the antecedent soil moisture content. Anthropogenic effects were found insignificant, with the exception in one of the studied micro-catchment. Effect of land use changes in most of the micro-catchments did not reflect in the shape of the flow duration curve because either the spatial extent of human impact was small and/or the overall basin slope was less than 20%.
Identifying controls on water chemistry of tropical cloud forest catchments: Combining descriptive approaches and multivariate analysis
(2010) Bücker, Amelie; Crespo, Patricio; Frede, Hans Georg; Vaché, Kellie B.; Cisneros, Felipe; Breuer, Lutz
We investigated controls on the water chemistry of a South Ecuadorian cloud forest catchment which is partly pristine, and partly converted to extensive pasture. From April 2007 to May 2008 water samples were taken weekly to biweekly at nine different subcatchments, and were screened for differences in electric conductivity, pH, anion, as well as element composition. A principal component analysis was conducted to reduce dimensionality of the data set and define major factors explaining variation in the data. Three main factors were isolated by a subset of 10 elements (Ca2?, Ce, Gd, K?, Mg2?, Na?, Nd, Rb, Sr, Y), explaining around 90% of the data variation. Land-use was the major factor controlling and changing water chemistry of the subcatchments. A second factor was associated with the concentration of rare earth elements in water, presumably highlighting other anthropogenic influences such as gravel excavation or road construction. Around 12% of the variation was explained by the third component, which was defined by the occurrence of Rb and K and represents the influence of vegetation dynamics on element accumulation and wash-out. Comparison of base- and fast flow concentrations led to the assumption that a significant portion of soil water from around 30 cm depth contributes to storm flow, as revealed by increased rare earth element concentrations in fast flow samples. Our findings demonstrate the utility of multi-tracer principal component analysis to study tropical headwater streams, and emphasize the need for effective land management in cloud forest catchments.
Model intercomparison to explore catchment functioning: results from a remote montane tropical rainforest
(2012) Plesca, Ina; Timbe Castro, Edison Patricio; Exbrayat, Jean Francois; Windhorst, David; Kraft, Philipp; Crespo Sánchez, Patricio Javier; Vaché, K. B.; Frede, Hans Georg; Breuer, Lutz
Catchment-scale runoff generation involves a complex interaction of physical and chemical processes operating over a wide distribution of spatial and temporal scales. Understanding runoff generation is challenged by this inherent complexity – the more uncertain step of predicting the hydrologic response of catchments is that much more challenging. Many different hypotheses have been implemented in hydrological models to capture runoff generation processes and provide hydrologic predictions. These concepts have been developed based on extended field observations. Here we propose inferring water flux understanding and catchment exploring through the application of a variety of available hydrological models as a mechanism to build upon and extend models that have been developed to capture particular hydrological processes. We view this ensemble modeling strategy as particularly appropriate in ungauged catchments. The study is carried out in a tropical montane rainforest catchment in Southern Ecuador. The catchment is 75 km2 and is covered by forest in the south, while the northern slopes have been partly deforested for grazing. Annual rainfall is highly variable, reaching up to 5700 mm per year in the upper parts of the catchment. To explore the dominating runoff processes, an ensemble of 6 hydrological models with different structures applied over different levels of both spatial and temporal detail was developed. The ensemble includes spatially lumped (HBV-light), semi-distributed (HEC-HMS, CHIMP, SWAT, LASCAM) and a fully distributed model (HBV-N-D). The hydro-statistical toolkit WETSPRO was used to characterize simulated and observed hydrographs. Estimated baseflow indices, flow minima and maxima, flow duration curves and cumulative errors were generated and compared among the ensemble of models. This process facilitated the exploration of processes controlling runoff generation, enabled an evaluation of the applicability of the screened models to tropical montane rainforests, and provided the capacity to evaluate and explain where different models failed.
Model intercomparison to explore catchment functioning: results from a remote montane tropical rainforest
(2012-07-24) Plesca, I.; Timbe, Edison; Exbrayat, J. F.; Windhorst, David; Kraft, P.; Crespo, P.; Vaché, Kellie B.; Frede, Hans Georg; Breuer, Lutz
Catchment-scale runoff generation involves a complex interaction of physical and chemical processes operating over a wide distribution of spatial and temporal scales. Understanding runoff generation is challenged by this inherent complexity – the more uncertain step of predicting the hydrologic response of catchments is that much more challenging. Many different hypotheses have been implemented in hydrological models to capture runoff generation processes and provide hydrologic predictions. These concepts have been developed based on extended field observations. Here we propose inferring water flux understanding and catchment exploring through the application of a variety of available hydrological models as a mechanism to build upon and extend models that have been developed to capture particular hydrological processes. We view this ensemble modeling strategy as particularly appropriate in ungauged catchments. The study is carried out in a tropical montane rainforest catchment in Southern Ecuador. The catchment is 75 km2 and is covered by forest in the south, while the northern slopes have been partly deforested for grazing. Annual rainfall is highly variable, reaching up to 5700 mm per year in the upper parts of the catchment. To explore the dominating runoff processes, an ensemble of 6 hydrological models with different structures applied over different levels of both spatial and temporal detail was developed. The ensemble includes spatially lumped (HBV-light), semi-distributed (HEC-HMS, CHIMP, SWAT, LASCAM) and a fully distributed model (HBV-N-D). The hydro-statistical toolkit WETSPRO was used to characterize simulated and observed hydrographs. Estimated baseflow indices, flow minima and maxima, flow duration curves and cumulative errors were generated and compared among the ensemble of models. This process facilitated the exploration of processes controlling runoff generation, enabled an evaluation of the applicability of the screened models to tropical montane rainforests, and provided the capacity to evaluate and explain where different models failed.
Multicriteria assessment of water dynamics reveals subcatchment variability in a seemingly homogeneous tropical cloud forest catchment
(2017) Timbe Castro, Edison Patricio; Feyen, Jan; Timbe Castro, Luis Manuel; Crespo Sánchez, Patricio Javier; Célleri Alvear, Rolando Enrique; Windhorst, David; Frede, Hans Georg; Breuer, Lutz
To improve the current knowledge of the rainfall–runoff phenomena of tropical montane catchments, we explored the usefulness of several hydrological indicators on a nested cloud forest catchment (76.9 km2). The used metrics belong to 5 categories: baseflow mean transit time, physicochemical properties of stream water, land cover, topographic, and hydrometric parameters. We applied diverse statistical techniques for data analysis and to contrast findings. Multiple regression analysis showed that mean transit times of base flow could be efficiently predicted by sodium concentrations (higher during baseflows) and temperatures of stream water, indicating a major influence of geomorphology rather than topographic or land cover characteristics. Principal component analysis revealed that no specific subset of catchment indicators could be identified as prevailing descriptors for all catchments. The agglomerative hierarchical clustering analysis provided concomitant results, implying larger levels of dissimilarity between smaller subcatchments than between larger ones. Overall, results point out an intricate interdependence of diverse processes at surface and subsurface level indicating a high level of heterogeneity. Disregarding heterogeneity of nested or paired catchments could lead to incomplete or misleading conclusions, especially in tropical mountain regions where pronounced spatial and temporal gradients are present.
Preliminary evaluation of the runoff processes in a remote montane cloud forest basin using mixing model analysis and mean transit time
(2012-12-15) Crespo, Patricio; Bücker, Amelie; Feyen, Jan; Vaché, Kellie B.; Frede, Hans Georg; Breuer, Lutz
In this study, the Mean Transit Time and Mixing Model Analysis methods are combined to unravel the runoff generation process of the San Francisco River basin (73.5 km2) situated on the Amazonian side of the Cordillera Real in the southernmost Andes of Ecuador. The montane basin is covered with cloud forest, sub-páramo, pasture and ferns. Nested sampling was applied for the collection of streamwater samples and discharge measurements in the main tributaries and outlet of the basin, and for the collection of soil and rock water samples. Weekly to biweekly water grab samples were taken at all stations in the period April 2007–November 2008. Hydrometric data, Mean Transit Time and Mixing Model Analysis allowed preliminary evaluation of the processes controlling the runoff in the San Francisco River basin. Results suggest that flow during dry conditions mainly consists of lateral flow through the C-horizon and cracks in the top weathered bedrock layer, and that all subcatchments have an important contribution of this deep water to runoff, no matter whether pristine or deforested. During normal to low precipitation intensities, when antecedent soil moisture conditions favour water infiltration, vertical flow paths to deeper soil horizons with subsequent lateral subsurface flow contribute most to streamflow. Under wet conditions in forested catchments, streamflow is controlled by near surface lateral flow through the organic horizon. Exceptionally, saturation excess overland flow occurs. By absence of the litter layer in pasture, streamflow under wet conditions originates from the A horizon, and overland flow.
Sampling frequency trade-offs in the assessment of mean transit times of tropical montane catchment waters under semi-steady-state conditions
(2015) Timbe Castro, Edison Patricio; Windhorst, David; Célleri Alvear, Rolando Enrique; Timbe Castro, Luis Manuel; Crespo Sánchez, Patricio Javier; Frede, Hans Georg; Feyen, Jan; Breuer, Lutz
Precipitation event samples and weekly based water samples from streams and soils were collected in a tropical montane cloud forest catchment for 2 years and analyzed for stable water isotopes in order to understand the effect of sampling frequency in the performance of three lumped-parameter distribution functions (exponential-piston flow, linear-piston flow and gamma) which were used to estimate mean transit times of waters. Precipitation data, used as input function for the models, were aggregated to daily, weekly, bi-weekly, monthly and bi-monthly sampling resolutions, while analyzed frequencies for outflows went from weekly to bi-monthly. By using different scenarios involving diverse sampling frequencies, this study reveals that the effect of lowering the sampling frequency depends on the water type. For soil waters, with transit times on the order of few weeks, there was a clear trend of over predictions. In contrast, the trend for stream waters, which have a more damped isotopic signal and mean transit times on the order of 2 to 4 years, was less clear and showed a dependence on the type of model used. The trade-off to coarse data resolutions could potentially lead to misleading conclusions on how water actually moves through the catchment, notwithstanding that these predictions could reach better fitting efficiencies, fewer uncertainties, errors and biases. For both water types an optimal sampling frequency seems to be 1 or at most 2 weeks. The results of our analyses provide information for the planning of future fieldwork in similar Andean or other catchments.
Solute behaviour and export rates in neotropical montane catchments under different land-uses
(2011-03-10) Bücker, Amelie; Crespo, Patricio; Frede, Hans Georg; Breuer, Lutz
To improve our knowledge of the influence of land-use on solute behaviour and export rates in neotropical montane catchments we investigated total organic carbon (TOC), Ca, Mg, Na, K, NO3 and SO4 concentrations during April 2007–May 2008 at different flow conditions and over time in six forested and pasture-dominated headwaters (0.7–76 km2) in Ecuador. NO3 and SO4 concentrations decreased during the study period, with a continual decrease in NO3and an abrupt decrease in February 2008 for SO4. We attribute this to changing weather regimes connected to a weakening La Niña event. Stream Na concentration decreased in all catchments, and Mg and Ca concentration decreased in all but the forested catchments during storm flow. Under all land-uses TOC increased at high flows. The differences in solute behaviour during storm flow might be attributed to largely shallow subsurface and surface flow paths in pasture streams on the one hand, and a predominant origin of storm flow from the organic layer in the forested streams on the other hand. Nutrient export rates in the forested streams were comparable to the values found in literature for tropical streams. They amounted to 6–8 kg ha−1 y−1 for Ca, 7–8 kg ha−1 y−1 for K, 4–5 kg ha−1y−1 for Mg, 11–14 kg ha−1 y−1 for Na, 19–22 kg ha−1 y−1 for NO3 (i.e. 4.3–5.0 kg ha−1 y−1 NO3-N) and 17 kg ha−1 y−1 for SO4. Our data contradict the assumption that nutrient export increases with the loss of forest cover. For NO3we observed a positive correlation of export value and percentage forest cover.
Stable water isotope tracing through hydrological models for disentangling runoff generation processes at the hillslope scale
(2014) Windhorst, David; Timbe Castro, Edison Patricio; Kraft, Philipp; Frede, Hans Georg; Breuer, Lutz
Hillslopes are the dominant landscape components where incoming precipitation becomes groundwater, streamflow or atmospheric water vapor. However, directly observing flux partitioning in the soil is almost impossible. Hydrological hillslope models are therefore being used to investigate the processes involved. Here we report on a modeling experiment using the Catchment Modeling Framework (CMF) where measured stable water isotopes in vertical soil profiles along a tropical mountainous grassland hillslope transect are traced through the model to resolve potential mixing processes. CMF simulates advective transport of stable water isotopes 18O and 2H based on the Richards equation within a fully distributed 2-D representation of the hillslope. The model successfully replicates the observed temporal pattern of soil water isotope profiles (R2 0.84 and Nash–Sutcliffe efficiency (NSE) 0.42). Predicted flows are in good agreement with previous studies. We highlight the importance of groundwater recharge and shallow lateral subsurface flow, accounting for 50 and 16% of the total flow leaving the system, respectively. Surface runoff is negligible despite the steep slopes in the Ecuadorian study region.