Browsing by Author "Buytaert, Wouter"

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Addressing sources of uncertainty in runoff projections for a data scarce catchment in the Ecuadorian Andes
(2014) Exbrayat, Jean Francois; Buytaert, Wouter; Timbe Castro, Edison Patricio; Windhorst, David; Breuer, Lutz
Future climate projections from general circulation models (GCMs) predict an acceleration of the global hydrological cycle throughout the 21st century in response to human-induced rise in temperatures. However, projections of GCMs are too coarse in resolution to be used in local studies of climate change impacts. To cope with this problem, downscaling methods have been developed that transform climate projections into high resolution datasets to drive impact models such as rainfall-runoff models. Generally, the range of changes simulated by different GCMs is considered to be the major source of variability in the results of such studies. However, the cascade of uncertainty in runoff projections is further elongated by differences between impact models, especially where robust calibration is hampered by the scarcity of data. Here, we address the relative importance of these different sources of uncertainty in a poorly monitored headwater catchment of the Ecuadorian Andes. Therefore, we force 7 hydrological models with downscaled outputs of 8 GCMs driven by the A1B and A2 emission scenarios over the 21st century. Results indicate a likely increase in annual runoff by 2100 with a large variability between the different combinations of a climate model with a hydrological model. Differences between GCM projections introduce a gradually increasing relative uncertainty throughout the 21st century. Meanwhile, structural differences between applied hydrological models still contribute to a third of the total uncertainty in late 21st century runoff projections and differences between the two emission scenarios are marginal.
Clay mineralogy of the soils in the south ecuadorian páramo region
(2005-07) Buytaert, Wouter; Sevink, J.; Leeuw, B. De; Deckers, Jozef
The pa´ramo soils of the mountainous upper Andean region (N3300 m a. s. l.) of the Rio Paute basin in central Ecuador are characterized by a thick, dark, highly organic epipedon and are classified as Andosols and Histosols. Their high water retention and buffering capacity play a key role in the hydrology of the region, which is subject to land use changes and increased cultivation. In the west (Western Cordillera), the soils are largely formed in the late Miocene and Pliocene volcanoclastic Tarqui formation, while in the east (Central Cordillera) they are formed in an older, mostly intermediate low-grade metamorphic rocks. Ten soil profiles were sampled and studied, using extraction techniques (oxalate and pyrophosphate) and XRD-techniques. Major differences in composition of the clay fractions were found that allow for distinction of three main groups of pa´ramo soils. A first group consists of soils influenced by recent volcanic ashes and dominated by organometallic complexes and with minor but distinct amounts of degraded mica, most probably formed by weathering of primary mica, present in these ashes. The second group comprises soils formed in volcanoclastic material of various Tertiary and earlier formations, containing residual primary and secondary crystalline clay-size minerals, as well as organometallic complexes whose genesis can be linked to the abundant presence of easily weatherable materials in these formations. A third group consists of soils in relicts of Tertiary, highly weathered regolith, formed under humid tropical conditions before the Andean uplift and occurring in the Central Cordillera. These soils contain kaolinite and gibbsite and develop into Histosols in the absence of significant organometallic complexation.
Comment on "Human impacts on headwater fluvial systems in the northern and central Andes" (Carol P. Harden, Geomorfología 79, 249 263)
(2008-04-01) Célleri, Rolando; Buytaert, Wouter; De Bièvre, Bert; Cisneros, Felipe; Wyseure, Guido; Deckers, Seppe
The high altitude grasslands of the tropical Andes, known as páramo, are a very fragile and unique ecosystem. Despite increasing human activities, many of its geomorphological and hydrological processes are still very poorly understood. We therefore welcome the paper of Harden [Harden, C.P., 2006. Human impacts on headwater fluvial systems in the northern and central Andes. Geomorphology 79, 249-263.] about "Human impacts on headwater fluvial systems in the northern and central Andes" as a valuable contribution to a better understanding of this complex ecosystem. However, in view of the available literature, we would like to complement the interpretation of the presented results and discuss some of the claims made in the paper.
Glaciers in Patagonia: controversy and prospects
(2012-05-29) Kargel, J. S.; Alho, P.; Buytaert, Wouter; Célleri, Rolando; Cogley, J. G.; Dussaillant, A.; Guido, Z.; Haeberli, W.; Harrison, S.; Leonard, G.; Maxwell, A.; Meier, C.; Poveda, G.; Reid, B.; Reynolds, J.; Rodriguez, C. A. P.; Romero, H.; Schneider, J.
Global climate change impacts on local climate and hydrology
(Springer, Berlin, Heidelberg, 2013) Timbe Castro, Edison Patricio
Global climate change will most likely have a severe impact on local climate and hydrological cycling in the tropical montane rainforest. We used a simple statistical downscaling technique for eight general circulation models and two IPCC AR4 emission scenarios (A1B, A2) to forecast feasible local climate conditions for the San Francisco river basin for three future time slices (2010–2039, 2040–2069, 2070–2099). These simulations were then used as forcing data for an ensemble of seven catchment scale rainfall-runoff models to investigate the effects on local hydrological fluxes. Precipitation for both emission scenarios is expected to increase, especially in the months May and June. These increases in precipitation input will lead to even more dynamic discharges as today. However, part of the increasing water input is compensated by raising evapotranspiration due to higher temperatures. Finally, we give an outlook on feasible future trends of water-related ecosystem services under climate change.
Human impact on the hydrology of the Andean páramos
(2006) Buytaert, Wouter; Célleri, Rolando; De Bièvre, Bert; Cisneros, Felipe; Wyseure, Guido; Deckers, Jozef; Hofstede, Robert
This paper analyses the problems involved in the conservation and management of the hydrological system of the South American páramo. The páramo consists of a collection of neotropical alpine grassland ecosystems covering the upper region of the northern Andes. They play a key role in the hydrology of the continent. Many of the largest tributaries of the Amazon basin have their headwaters in the páramo. It is also the major water source for the Andean highlands and a vast area ofarid and semi-arid lowlands, where páramo water is used for domestic, agricultural and industrial consumption, and the generation of hydropower. Recently, the páramo is increasingly used for intensive cattle grazing, cultivation, and pine planting, among others. These activities, as well as global phenomena such as climate change, severely alter the hydrological regime. A review on the state of knowledge of its hydrology is given in a first part. In a second part, the impact of human activities and climate change on the hydrology of the páramo is discussed.
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%.
Impact of land use changes on the hydrological properties of volcanic ash soils in South Ecuador
(2002-06) Buytaert, Wouter; Deckers, Jozef; Dercon, Gerd; Bievre, Bert De; Poesen, Jean; Govers, Gerard
The effect of land use on the water retention capacity of Umbric Andosols in south Ecuador was studied. The objective was to acquire a better insight into the hydrological processes of the ecosystem and the role of the soil, in order to assess the impact of changing soil properties due to land use change on the hydrology of the high Andes region. Field data on the water retention capacity at wilting point of Umbric Andosols were collected for both cultivated field conditions and original bush vegetation. The pH in water and in NaF, texture, organic matter content and dry bulk density were measured to show which physicochemical soil characteristics are responsible for the water retention of the Umbric Andosols and for the irreversible loss in water retention due to air drying. Organic matter content appears to be very important and certainly more important than allophane clay content. Water retention of the organic litter layer was calculated to be 16 mm, this would be lost when vegetation was cleared and the land cultivated.
Land use change impacts on the hydrology of wet Andean páramo ecosystems
(International Association of Hydrological Sciences, 2009) Crespo Sánchez, Patricio Javier; Borja Ramón, Pablo Marcelo; Célleri Alvear, Rolando Enrique; Feyen, Jean; Buytaert, Wouter; De Bievre, Bert; Iñiguez Moran, Vicente Mauricio; Crespo Sánchez, Patricio Javier
This paper presents the research performed in the wet Andean páramo ecosystem in order to study the land use change impacts on its hydrology, using small paired catchments. The research results revealed that pine plantations produce a decrease of annual water yield as a consequence of increased evapotranspiration. On the other hand, livestock grazing does not seem to affect the hydrological response, primarily due to the low animal density. The main impact of cultivation is the reduction in the regulating function of the catchment, with a large increase in the magnitude of peak flows and a reduction of base flows. Furthermore, research results revealed that vertical infiltration through the soil is dominant under wet conditions, whereas preferential flow within the organic horizon to the underlying mineral horizon is dominant during low intensity rains. Saturated excess surface flow is observed only during long rain events; otherwise near surface lateral flow in the organic layer occurs. There is no evidence of Hortonian flow
Predicting climate change impacts on water resources in the tropical Andes: Effects of GCM uncertainty
(2009-04-16) Buytaert, Wouter; Célleri, Rolando; Timbe, Luis
There is a strong demand from policy makers for predictions about the potential impacts of climate change on water resources. Integrated environmental models, combining climatic and hydrologic models, are often used for this purpose. This paper examines the impact of uncertainties related to GCMs in hydrological impact studies in the tropical Andes. A conceptual hydrological model is calibrated on data from four mesoscale, mountainous catchments in south Ecuador. The model inputs are then perturbed with anomalies projected by 20 GCMs available from the IPCC Data Distribution Centre. The results show that on average, the average monthly discharge is not expected to change dramatically. However, the simulated discharges driven by different global climate model forcing data can diverge widely, with prediction ranges often surpassing current discharge.
Regional variability of volcanic ash soils in south Ecuador: the relation with parent material, climate and land use
(2007) Buytaert, Wouter; Deckers, Jozef; Wyseure, Guido
The high Andes region of south Ecuador is characterised by intense land use changes. These changes affect particularly the páramo, which is a collection of high altitudinal grassland ecosystems. In this region, the interaction between airborne volcanic ashes and the cold and wet climate results in very typical soils, with an elevated organic C contents. The physical soil properties are closely related to the high and reliable base flow in rivers descending from the páramo, which makes them important for the socio-economic development of the region. In this study, we analyse the regional variability of the soils in the south Ecuadorian rio Paute basin. In a first part of the study, data from soil profiles along north–south transects are used to determine the soil properties, and to relate the spatial variability of these properties to the major trends in parent material, volcanic ash deposits and climate. The profiles are Histic Andosols and Dystric Histosols devoid of allophane, with very high amounts of organic matter. Significant differences between the western and central mountain range are observed, as well as a general decrease in Andic properties from north to south, coinciding with the decrease in volcanic influence. Finally, the impact of human activities on the soil properties is assessed in a case study in the Machangara valley. Data from 5 profiles, located in an area with natural grass vegetation and a low degree of human impact are compared with 4 profiles in a heavily disturbed, intensively drained cultivated area. Despite the intensity of the land use, very few significant differences are found.
Space-time rainfall variability in the Paute basin, Ecuadorian Andes
(2007-06-08) Célleri, Rolando; Willems, Patrick; Buytaert, Wouter; Feyen, Jan
Despite the importance of mountain ranges as water providers, knowledge of their climate variability is still limited, mostly due to a combination of data scarcity and heterogeneous orography. The tropical Andes share many of the main features of mountain ranges in general, and are subject to several climatic influences that have an effect on rainfall variability. Although studies have addressed the large-scale variation, the basin scale has received little attention. Thus, the purpose of this study was to obtain a better understanding of rainfall variability in the tropical Andes at the basin scal, utilizing the Paute River basin of southern Ecuador as a case study. Analysis of 23 rainfall stations revealed a high spatial variability in terms of: (i) large variations of mean annual precipitation in the range 660–3400 mm; (ii) the presence of a non-monotonic relation between annual precipitation and elevation; and (iii) the existence of four, sometimes contrasting, rainfall regimes. Data from seven stations for the period 1964–1998 was used to study seasonality and trends in annual, seasonal and monthly precipitation. Seasonality is less pronounced at higher elevations, confirming that in the páramo region, the main water source for Andean basins, rainfall is well distributed year round. Additionally, during the period of record, no station has experienced extreme concentrations of annual rainfall during the wet season, which supports the concept of mountains as reliable water providers. Although no regional or basin-wide trends are found for annual precipitation, positive (negative) trends during the wet (dry) season found at four stations raises the likelihood of both water shortages and the risk of precipitation-triggered disasters. The study demonstrates how variable the precipitation patterns of the Andean mountain range are, and illustrates the need for improved monitoring
Spatial and temporal rainfall variability in mountainous areas: A case study from the south Ecuadorian Andes
(2006-10-15) Buytaert, Wouter; Célleri, Rolando; Willems, Patrick; Bievre, Bert De; Wyseure, Guido
Particularly in mountain environments, rainfall can be extremely variable in space and time. For many hydrological applications such as modelling, extrapolation of point rainfall measurements is necessary. Decisions about the techniques used for extrapolation, as well as the adequacy of the conclusions drawn from the final results, depend heavily on the magnitude and the nature of the uncertainty involved. In this paper, we examine rainfall data from 14 rain gauges in the western mountain range of the Ecuadorian Andes. The rain gauges are located in the western part of the rio Paute basin. This area, between 3500 and 4100 m asl, consists of mountainous grasslands, locally called páramo, and acts as major water source for the inter-Andean valley. Spatial and temporal rainfall patterns were studied. A clear intraday pattern can be distinguished. Seasonal variation, on the other hand, is low, with a difference of about 100 mm between the dryest and the wettest month on an average of about 100 mm month−1, and only 20% dry days throughout the year. Rain gauges at a mutual distance of less than 4000 m are strongly correlated, with a Pearson correlation coefficient higher than 0.8. However, even within this perimeter, spatial variability in average rainfall is very high. Significant correlations were found between average daily rainfall and geographical location, as well as the topographical parameters slope, aspect, topography. Spatial interpolation with thiessen gives good results. Kriging gives better results than thiessen, and the accuracy of both methods improves when external trends are incorporated.
The effect of land-use changes on the hydrological behaviour of histic andosols in south Ecuador
(2005-12) Buytaert, Wouter; Wyseure, Guido; Bievre, Bert De; Deckers, Jozef
The south Ecuadorian Andean mountain belt between 3500 and 4500 m altitude is covered by a highly endemic and fragile ecosystem called paramo. The Histic Andosols covering this regi ´ on have highly developed hydric properties and exert a key function in the hydrological regulation of the paramo ecosystem. Unlike most Andosols, their extreme ´water retention capacity is not due to the presence of typical minerals such as allophane or imogolite. Although these minerals are virtually absent, the large organic carbon content, due to organometallic complexation, gives rise to similar properties. The water content at 1500 kPa can exceed 2000 g kg 1, and the high hydraulic conductivity at saturation (about 15 mm h 1) drops sharply when low suction is applied. The three methods applied, i.e. the inverted auger hole, the tension infiltrometer and the constant-head permeameter method, give very similar results. The paramo ´is characterized by a slow hydrological response and a good water regulation, caused by the combination of a high water storage capacity and high conductivity. The wide pore size distribution of the organometallic complexes results in a water retention curve that differs significantly from the classic Mualem–Van Genuchten description, but can better be described with a simple linear or semilogarithmic model. The soils investigated are very prone to irreversible structural changes caused by land-use changes. The conversion of natural land for cultivation has a large impact on the hydrological function of the region. The water storage capacity increases by 5 to 30%, and the hydraulic conductivity is 31% higher in cultivated catchments. These changes are related to a larger peak flow, a smaller base flow and generally a smaller discharge buffering capacity, despite the higher storage capacity. Copyright  2005 John Wiley & Sons, Ltd
The effect of natural infrastructure on water erosion mitigation in the Andes
(2022) Ochoa Tocachi, Boris Fernando
Soil erosion by water is affecting natural and anthropogenic environments through its impacts on water quality and availability, loss of soil nutrients, flood risk, sedimentation in rivers and streams, and damage to civil infrastructure. Sustainable management aims to avoid, reduce and reverse soil erosion and can provide multiple benefits for the environment, population, and livelihoods. We conducted a systematic review of 121 case studies from the Andes to answer the following questions: (1) Which erosion indicators allow us to assess the effectiveness of natural infrastructure? (2) What is the overall impact of working with natural infrastructure on on-site and off-site erosion mitigation? and (3) Which locations and types of studies are needed to fill critical gaps in knowledge and research? Three major categories of natural infrastructure were considered: protective vegetation, soil and water conservation measures, and adaptation measures that regulate the flow and transport of water. From the suite of physical, chemical and biological indicators commonly used in soil erosion research, two indicators were particularly relevant: soil organic carbon (SOC) of topsoil, and soil loss rates at the plot scale. In areas with protective vegetation and/or soil and water conservation measures, the SOC of topsoil is –on average– 1.3 to 2.8 times higher than in areas under traditional agriculture. Soil loss rates in areas with natural infrastructure were reported to be 38 % to 54 % lower than rates measured in untreated croplands. Further research is needed to evaluate whether the reported effectiveness holds during extreme events related to, for example, El Niño–Southern Oscillation.
The effects of afforestation and cultivation on water yield in the Andean páramo
(2007-10) Buytaert, Wouter; De Bièvre, Bert; Iñiguez, Vicente
Over the last decades, the Andean highlands of Ecuador have been characterised by intense afforestation efforts, in order to increase the economic return of less viable agricultural areas, reduce erosion and, more recently, to sequestrate atmospheric carbon. Afforestation with Pinus species is widespread in the high altitudinal grasslands known as pa´ramos. The impact of Pinus patula afforestation on the water yield is studied and compared to the more common practice of intensive grazing and potato cultivation in four microcatchments in the Paute river basin in south Ecuador. Two catchments are covered with natural grassland vegetation, one is converted to pine forest, and one is drained, partly intensively grazed, and partly cultivated with potatoes. The results indicate that afforestation with P. patula reduces the water yield by about 50%, or an average of 242 mm year1 . The water yield of the cultivated catchment is very similar to that of the natural catchments, but analysis of the flow duration curves suggests a faster response and a loss of base flow. These effects may have important implications for a sustainable management of the páramo ecosystem, given that the pa´ramo is the major water supplier for the Andean highlands.
The impact of pine plantations on water yield: a case study from the Ecuadorian Andes
(2007) Buytaert, Wouter; Célleri, Rolando; Bievre, Bert De; Iñiguez, Vicente
The conversion of natural grasslands to both pine plantations and cultivation was studied in the South American tropical alpine ecosystem called páramo. Hydrological and meteorological data were collected from four microcatchments, each with predominant vegetation,. The water balance was analysed in order to obtain the evapotranspiration of each catchment. The natural grasslands catchments had the lowest evapotranspiration. Evaporation in the cultivated catchment was about 20-40% higher, compared to 40-70% in the pine catchment. Flow duration curves were derived from the discharge time series and used to assess differences in the hydrological response of the catchments. The cultivated catchment is characterized by a significantly faster hydrological response than the natural catchment. The flow duration curves show higher peak flows and lower base flows. In the pine catchment, both peak and base flow are drastically lower because of higher local consumption. In the past, pine plantations have been widely considered as a viable method to improve the economic return of the páramo. In view of the importance of the páramo as a water supplier, these activities might need to be re-evaluate
The use of the linear reservoir concept to quantify the impact of changes in land use on the hydrology of catchments in the Andes
(2004) Buytaert, Wouter; Wyseure, Guido; Deckers, Jozef; De Bièvre, Bert
The high Andes region of South Ecuador (The Paramo) is characterized by a cold and wet climate. Most soils of the Páramo region are Andosols and Histosols, with a very high water retention capacity that is affected irreversibly by drying. This key property of Páramo soils buffers catchment outflow, resulting in an almost uniform outflow pattern which, notwithsyanding the variability in rainfall, can be very variable in space and time. These soils serve as the most important reservoir of drinking and irrigation water for the densely populated inter-Andean depression region. The Páramo has long served only as an extensive grazing area but recent population pressure and land scarcity have increased cultivation. Two small Páramo catchments (about 2 km2) were monitored intensively for precipitation and discharge for over a year to assess the effect of such land-use changes on the hydrological properties. One catchment is in an undisturbed area and grazed intensively while in the other, local farmers started intensive drainage for cultivation of potatoes about five years ago. The linear reservoir concept has been used to assess the overall retention capacity of the catchment in terms of both peak response and base flow. In this model, every catchment is considered as a series if independent parallel reservoirs, each characterized by mean residence times (T). In every catchment, three major mean residence time can be distinguished. In the undisturbed catchment, an immediate response. characterized by a T of 5.4 hours, is followed by a slower response with a T of 44.3h. The base flow has mean T value of 360 h. The response of the cultivated catchment is similar with T values of 3.6 h., 27.2 h and 175 h, respectively. As a result, in the disturbed catchment, water release is about 40% faster than in the undisturbed catchment, so that the base flow falls rapidly to lower levels. The linear reservoir model is a simple way of quantifying the impact of land use changes on the water regulation capacity of Páramo catchments.
Uncertainties in climate change projections and regional downscaling in the tropical Andes: Implications for water resources management
(2010-07-15) Buytaert, Wouter; Vuille, M.; Dewulf, A.; Urrutia, R.; Karmalkar, Ambarish; Célleri, Rolando
Climate change is expected to have a large impact on water resources worldwide. A major problem in assessing the potential impact of a changing climate on these resources is the difference in spatial scale between available climate change projections and water resources management. Regional climate models (RCMs) are often used for the spatial disaggregation of the outputs of global circulation models. However, RCMs are time-intensive to run and typically only a small number of model runs is available for a certain region of interest. This paper investigates the value of the improved representation of local climate processes by a regional climate model for water resources management in the tropical Andes of Ecuador. This region has a complex hydrology and its water resources are under pressure. Compared to the IPCC AR4 model ensemble, the regional climate model PRECIS does indeed capture local gradients better than global models, but locally the model is prone to large discrepancies between observed and modelled precipitation. It is concluded that a further increase in resolution is necessary to represent local gradients properly. Furthermore, to assess the uncertainty in downscaling, an ensemble of regional climate models should be implemented. Finally, translating the climate variables to streamflow using a hydrological model constitutes a smaller but not negligible source of uncertainty.
Understanding the hydrology of tropical Andean ecosystems through an Andean network of basins
(2009-03-30) Célleri, Rolando; Buytaert, Wouter; De Bièvre, Bert; Tobón, Conrado; Crespo, Patricio; Molina, Jorge; Feyen, Jan
During the last decade several initiatives aiming at conserving and protecting the water provision of Andean ecosystems have started. However, their application have faced a number of limitations from the technical side mainly due to the lack of knowledge of hydrological processes and Andean-specific developed and tested hydrological models for scenario analyses. The large variability found in ecosystems, climates and geomorphological settings makes hydrological research a complex task and answers to these societal problems therefore may take too long, unless a well coordinated collaboration between research centres, NGO’s and local governments take place. This manuscript outlines the goals of a regional initiative on participatory-based networking of data monitoring; describes how researchers can help local and regional stakeholders and vice-versa with data collection, processing, storage and dissemination; highlights the benefits of the collaboration for the scientific community and policy makers; and proposes measures to make the collaboration effective and sustainable.