Hydrological snowmelt modelling in snow covered river basins be means of geographic information system and remote sensing: case study - Latyan catchment in Iran

In mountainous watersheds snow melt can have a significant impact on the water balance and at certain times of the year it could be the most important contribution to runoff. In many parts of the world snow act as natural reservoirs that can play an important role for water supply. Alas, despite its importance, many of snow driven basins suffer from a lack of hydrological infrastructure and equipment so they cannot be described adequately in terms of snow hydrological dynamics. Because of limited accessibility are the few observation stations in such areas very rarely located in the higher elevations but are concentrated mostly in the middle and low elevation resulting in an underrepresentation in data availability of the high altitudes which are important for the process dynamics. Thus the modelling of snow hydrological dynamics in mountainous regions such as the Latyan catchment is often difficult. Reasons for this are in addition to the aforementioned data availability, topographic effects and gradients that can make a spatial interpolation of the input data and the model states a complicated task. Especially in semi-arid regions, high-altitude headwater basins with a significant snow component have a large potential by balancing and distributing scarce water resources. Particular here, a quantitative assessment of the spatial distribution of snow cover and snow processes are an important basis for a sound water management and for the hydrological forecasting and risk prevention. Therefore, the water management in such regions could benefit from reliable predictions of the hydrological dynamics derived from model based studies. Suitable models should represent the physical basis and hydrological processes that simulate the system’s response, fairly well. In this study the spatially distributed process-oriented hydrological model J2000g was used for the 700 km² large Latyan catchment in Iran. The target was to derive spatially distributed estimates of the quantity and timing of hydrological balance terms and state variables like rainfall, actual evapotranspiration (AET), runoff, snow water equivalent (SWE) and snow melt. The model uses the distribution concept of Hydrological Response Units (HRU) to take the spatial variability in the basin into account. The model simulates for each HRU and each time step snow accumulation and snow melt, soil water content, the actual evapotranspiration, groundwater recharge and runoff generation distributed into two components – direct runoff and ground water runoff. The fact that J2000g cannot account for anthropogenetic influences and natural water losses as they occur in karsts regions made the selection of suitable sub-basin for model calibration a difficult task. However, three sub-basins Roodak, Najarkola and Naran could be identified which underground is characterized mainly by impervious bed rock and which have only minimal anthropogenic influences. The sizes of the three sub-basins are between 31 to 430 km². For each of these sub-basins, the model parameters were calibrated automatically by means of Monte-Carlo analysis and the Shuffled Complex Evolution (SCE-UA) calibration procedure. The calibration was done by the comparison with measured runoff values for the period from October 1990 to September 2001 in monthly time steps using the Nash-Sutcliffe efficiency as the objective function. In addition, for each sub-basin the spatial distribution of rainfall, runoff, actual evapotranspiration, snow melt and snow water equivalent was analysed and compared with corresponding measurements. The snow module of the J2000g model was developed and checked against measured values of nine snow observation stations, which were located within the test basins. For each of the observation stations the corresponding HRUs were extracted and separate models calibrated were calibrated using the measured SWE. The model quality was quantified by using the Nash-Sutcliffe efficiency (NSE) and the coefficient of determination (r²) as objective functions. The comparison with the calibrated catchment models showed that accumulation and melting of the snowpack could be simulated reasonably well at all stations but the results were less good than those of the separately calibrated catchment models. The comparison of the separate SWE models resulted in values between 0.28 - 0.68 for NSE and values between 0.53 - 0.83 for r². For the catchment models the comparison of the simulated runoff with measured data showed NSE values between 0.78 and 0.82. By these values it can be stated that the hydrological dynamics and the snow processes of the three sub-basins within the Latyan catchment could be simulated sufficiently well with J2000g. Finally, a "global" parameter set for whole the Latyan catchment was generated by an area-weighted mean of the parameters from the calibrated sub-basin models. With this parameter set Nash-Sutcliffe efficiencies between 0.68 and 0.79 could be obtained for Latyan. It can be summarized that the single modules and in particular the snow components of J2000g along with the HRU distribution approach can be considered as suitable for the given project objectives i.e. the assessment of the hydrological dynamics of the Latyan catchment. Hereby, the model can be used to elaborate important hydrological information for a sustainable management of the water resources.In gebirgigen Einzugsgebieten kann die Schneeschmelze einen entscheidenden Einfluss auf die Wasserbilanz haben und zu gewissen Zeiten im Jahr der wichtigste Beitrag zur Abflussbildung sein. In vielen Teilen der Welt stellen Schneedecken natürliche Speicher dar, die eine wichtige Rolle für die Wasserversorgung einnehmen können. Trotz ihrer großen Bedeutung leiden aber viele dieser schneebeeinflussten Einzugsgebiete an einer mangelhaften hydrologischen Infrastruktur und Ausstattung wodurch sie hinsichtlich der schneehydrologischen Dynamik nur unzureichend beschrieben werden können. Aus Gründen der Erreichbarkeit sind die wenigen Beobachtungsstationen in solchen Gebieten nur sehr selten in den höheren Lagen lokalisiert sondern meist in den mittleren und geriengeren Höhen konzentriert wodurch die für die Dynamik wichtigen Hochlagen hinsichtlich der Datenverfügbarkeit unterrepräsentiert sind. Hierdurch ist die Modellierung der schneehydrologischen Dynamik in gebirgigen Regionen wie dem Latyan Einzugsgebiet oft schwierig. Gründe hierfür sind neben der bereits angesprochenen Datenverfügbarkeit auch topographische Effekte und Gradienten, die eine räumliche Interpolation der Eingangsdaten und der Modellzustände deutlich erschweren können. Besonders in semi-ariden Regionen besitzen hoch gelegene Quelleinzugsgebiete mit einer deutlich ausgeprägten Schneekomponente aufgrund ihres Potentials, als Ausgleich und Verteiler von knappen Wasserressourcen zu wirken, eine große Bedeutung. Hier ist aber ganz besonders eine quantitative Erfassung der räumlichen Ausprägung von Schneedecken und der Schneeprozesse eine wichtige Grundlage für ein fundiertes Wassermanagement und für die hydrologische Vorhersage und die Risikovorbeugung von großer Bedeutung. Insbesondere das Wassermanagement könnte von einer verlässlichen Vorhersage der hydrologischen Dynamik basierend auf Modellstudien in solchen Gebieten deutlich profitieren. Hierzu werden Modelle benötigt, die die physikalischen Grundlagen und die hydrologischen Prozesse, die die Gebietsantwort kontrollieren, hinreichend genau abbilden können. In dieser Studie wurde das räumlich distributive, prozessorientierte hydrologische Modell J2000g für das ca. 700 km² große Latyan Einzugsgebiet im Iran angewendet. Das Ziel war eine räumlich verteilte Abschätzungen bezüglich der Menge und der zeitlichen Verteilung der hydrologischen Bilanzglieder und Zustandsgrößen Niederschlag, aktuelle Verdunstung (AET), Abflussbildung, Schneewasseräquivalent (SWÄ) und Schneeschmelze zu liefern. Das Modell nutzt das Distributionskonzept der Hydrological Response Units (HRU) um die räumliche Variabilität im Einzugsgebiet zu berücksichtigen. Das Modell berechnet für jede HRU und jeden Zeitschritt die Schneeakkumulation und Schneeschmelze, den Bodenwassergehalt, die aktuelle Verdunstung, die Grundwasserneubildung und die Abflussbildung in zwei Komponenten – Direktabfluss und Grundwasserabfluss. Die Tatsache, dass J2000g keine anthropogenen Einflüsse und auch natürliche Wasserverluste, wie sie z.B. in Karstregionen auftreten können, berücksichtigt, erschwerte die Auswahl an Teileinzugsgebieten für die Modellkalibrierung. Dennoch konnten drei Teileinzugsgebiete Roodak, Najarkola und Naran identifiziert werden deren Untergrund weitestgehend durch undurchlässige Gesteine geprägt sind und die nur minimale anthropogene Einflüsse aufweisen. Die Größen der drei Gebiete liegen zwischen 31 und 430 km². Für jedes dieser Gebiete wurden die Modellparameter automatisch mit Hilfe der Monte-Carlo-Analyse und dem Shuffled-Complex-Evolution (SCE-UA) Verfahren kalibriert. Die Kalibrierung erfolgte anhand gemessener monatlicher Werte für die Periode von Oktober 1990 bis September 2001 wobei die Nash-Sutcliffe Effizienz als Gütekriterium eingesetzt wurde. Zusätzlich wurde für jedes Einzugsgebiet die räumliche Verteilung von Niederschlag, Abfluss, aktueller Verdunstung, Schneeschmelze und Schneewasseräquivalent analysiert und mit entsprechenden Messwerten verglichen. Die Schneewasseräquivalentmodellierung wurde mit Messwerten von neun Schneebeobachtungsstationen, die innerhalb der Testeinzugsgebiete lagen überprüft. Hierzu wurden diejenigen HRU, die der Lokalisierung der Beobachtungsstationen entsprachen, extrahiert und separate Modelle für diese HRU anhand der SWÄ Messwerte kalibriert. Die Modellqualität wurde mit der Nash-Sutcliffe Effizienz (NSE) und dem Bestimmtheitsmaß (r²) quantifiziert. Der Vergleich mit den kalibrierten Einzugsgebietsmodellen zeigte, dass diese den Schneedeckenauf- und –abbau an den Vergleichsstationen hinreichend gut simulieren können, dass sie aber schlechtere Ergebnisse als die separat kalibrierten Modelle ergaben. Der Vergleich der separaten Modelle ergab Werte zwischen 0.28 – 0.68 für NSE und Werte zwischen 0.53 – 0.83 für r². Für die Einzugsgebietsmodelle und dem Vergleich des simulierten Abfluss mit Messwerten ergab NSE Werte zwischen 0.78 und 0.82. Hierdurch konnte belegt werden, dass die hydrologische Dynamik und auch die Schneeprozesse in den Latyan Teileinzugsgebiet mit J2000g hinreichend gut wiedergegeben werden können. Schließlich wurde mit Hilfe einer flächenbasierten Gewichtung aus den Parametern der kalibrierten Teileinzugsgebiete ein „globaler“ Parametersatz für das gesamte Latyan Einzugsgebiet erzeugt. Mit diesem Parametersatz wurden Nash-Sutcliffe Effizienzen zwischen 0.68 und 0.79 für das Latyan Einzugsgebiet erzielt. Es kann zusammenfassend festgestellt werden, dass die einzelnen Module und insbesondere die Schneekomponenten des J2000g sowie das HRU Konzept für die erzielte Fragestellung der Erfassung der hydrologischen Dynamik des Latyan Einzugsgebiet als sehr gut geeignet betrachtet werden können. Hierdurch können mit dem Modell wichtige hydrologische Grundlagen für eine nachhaltige Bewirtschaftung der Wasserressourcen erarbeitet werden

Consequences of architecture and resource allocation for growth dynamics of bunchgrass clones.

Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.In order to understand how bunchgrasses achieve dominance over other plant growth forms and how they achieve dominance over one another in different environments, it is first necessary to develop a detailed understanding of how their growth strategy interacts with the resource limits of their environment. Two properties which have been studied separately in limited detail are architecture and disproportionate resource allocation. Architecture is the structural layout of organs and objects at different hierarchical levels. Disproportionate resource allocation is the manner in which resources are allocated across objects at each level of hierarchy. Clonal architecture and disproportionate resource allocation may interact significantly to determine the growth ability of clonal plants. These interactions have not been researched in bunchgrasses. This thesis employs a novel simulation technique, functional-structural plant modelling, to investigate how bunchgrasses interact with the resource constraints imposed in humid grasslands. An appropriate functional-structural plant model, the TILLERTREE model, is developed that integrates the architectural growth of bunchgrasses with environmental resource capture and disproportionate resource allocation. Simulations are conducted using a chosen model species Themeda triandra, and the environment is parameterised using characteristics of the Southern Tall Grassveld, a humid grassland type found in South Africa. Behaviour is considered at two levels, namely growth of single ramets and growth of multiple ramets on single bunchgrass clones. In environments with distinct growing and non-growing seasons, bunchgrasses are subjected to severe light depletion during regrowth at the start of each growing season because of the accumulation of dead material in canopy caused by the upright, densely packed manner in which they grow. Simulations conducted here indicate that bunchgrass tillers overcome this resource bottleneck through structural adaptations (etiolation, nonlinear blade mass accretion, residual live photosynthetic surface) and disproportionate resource allocation between roots and shoots of individual ramets that together increase the temporal resource efficiency of ramets by directing more resources to shoot growth and promoting extension of new leaves through the overlying dead canopy. The architectural arrangement of bunchgrasses as collections of tillers and ramets directly leads to consideration of a critical property of clonal bunchgrasses: tiller recruitment. Tiller recruitment is a fundamental discrete process limiting the vegetative growth of bunchgrass clones. Tiller recruitment occurs when lateral buds on parent tillers are activated to grow. The mechanism that controls bud outgrowth has not been elucidated. Based on a literature review, it is here proposed that lateral bud outgrowth requires suitable signals for both carbohydrate and nitrogen sufficiency. Subsequent simulations with the model provide corroborative evidence, in that greatest clonal productivity is achieved when both signals are present. Resource allocation between live structures on clones may be distributed proportionately in response to sink demand or disproportionately in response to relative photosynthetic productivity. Model simulations indicate that there is a trade-off between total clonal growth and individual tiller growth as the level of disproportionate allocation between ramets on ramet groups and between tillers on ramets increases, because disproportionate allocation reduces tiller population size and clonal biomass, but increases individual tiller performance. Consequently it is proposed that different life strategies employed by bunchgrasses, especially annual versus perennial life strategies, may follow more proportionate and less proportionate allocation strategies respectively, because the former favours maximal resource capture and seed production while the latter favours individual competitive ability. Structural disintegration of clones into smaller physiologically integrated units (here termed ramet groups) that compete with one another for resources is a documented property of bunchgrasses. Model simulations in which complete clonal integration is enforced are unable to survive for long periods because resource bottlenecks compromise all structures equally, preventing them from effectively overcoming resource deficits during periods when light is restrictive to growth. Productivity during the period of survival is also reduced on bunchgrass clones with full integration relative to clones that disintegrate because of the inefficient allocation of resources that arises from clonal integration. This evidence indicates that clonal disintegration allows bunchgrass clones both to increase growth efficiency and pre-empt potential death, by promoting the survival of larger ramet groups and removing smaller ramet groups from the system. The discrete nature of growth in bunchgrasses and the complex population dynamics that arise from the architectural growth and the temporal resource dynamics of the environment, may explain why different bunchgrass species dominate under different environments. In the final section this idea is explored by manipulating two species tiller traits that have been shown to be associated with species distributions across non-selective in defoliation regimes, namely leaf organ growth rate and tiller size (mass or height). Simulations with these properties indicate that organ growth rate affects daily nutrient demands and therefore the rate at which tillers are terminated, but had only a small effect on seasonal resource capture. Tiller mass size affects the size of the live tiller population where smaller tiller clones maintain greater numbers of live tillers, which allows them to them to sustain greater biomass over winter and therefore to store more reserves for spring regrowth, suggesting that size may affect seasonal nitrogen capture. The greatest differences in clonal behaviour are caused by tiller height, where clones with shorter tillers accumulate substantially more resources than clones with taller tillers. This provides strong evidence there is trade-off for bunchgrasses between the ability to compete for light and the ability to compete for nitrogen, which arises from their growth architecture. Using this evidence it is proposed that bunchgrass species will be distributed across environments in response to the nitrogen productivity. Shorter species will dominate at low nitrogen productivity, while taller species dominate at high nitrogen productivity. Empirical evidence is provided in support of this proposal

Anales del XIII Congreso Argentino de Ciencias de la Computación (CACIC)

Contenido: Arquitecturas de computadoras Sistemas embebidos Arquitecturas orientadas a servicios (SOA) Redes de comunicaciones Redes heterogéneas Redes de Avanzada Redes inalámbricas Redes móviles Redes activas Administración y monitoreo de redes y servicios Calidad de Servicio (QoS, SLAs) Seguridad informática y autenticación, privacidad Infraestructura para firma digital y certificados digitales Análisis y detección de vulnerabilidades Sistemas operativos Sistemas P2P Middleware Infraestructura para grid Servicios de integración (Web Services o .Net)Red de Universidades con Carreras en Informática (RedUNCI

Anales del XIII Congreso Argentino de Ciencias de la Computación (CACIC)

Contenido: Arquitecturas de computadoras Sistemas embebidos Arquitecturas orientadas a servicios (SOA) Redes de comunicaciones Redes heterogéneas Redes de Avanzada Redes inalámbricas Redes móviles Redes activas Administración y monitoreo de redes y servicios Calidad de Servicio (QoS, SLAs) Seguridad informática y autenticación, privacidad Infraestructura para firma digital y certificados digitales Análisis y detección de vulnerabilidades Sistemas operativos Sistemas P2P Middleware Infraestructura para grid Servicios de integración (Web Services o .Net)Red de Universidades con Carreras en Informática (RedUNCI