Improved Modeling of Evapotranspiration using Satellite Remote Sensing at Varying Spatial and Temporal Scales

The overall objective of the dissertation was to improve the spatial and temporal representation and retrieval accuracy of evapotranspiration (ET) using satellite imagery. Specifically, (1) aiming at improving the spatial representation of daily net radiation (Rn,24) under rugged terrains, a new algorithm, which accounts for terrain effects on available shortwave radiation throughout a day and utilizes four observations of Moderate-resolution Imaging Spectroradiometer (MODIS)-based land surface temperature retrievals to simulate daily net longwave radiation, was developed. The algorithm appears to be capable of capturing heterogeneity in Rn,24 at watershed scales. (2) Most satellite-based ET models are constrained to work under cloud-free conditions. To address this deficiency, an approach of integrating a satellite-based model with a large-scale feedback model was proposed to generate ET time series for all days. Results show that the ET time series estimates can exhibit complementary features between the potential ET and the actual ET at watershed scales. (3) For improving the operability of Two-source Energy Balance (TSEB) which requires computing resistance networks and tuning the Priestley-Taylor parameter involved, a new Two-source Trapezoid Model for ET (TTME) based on deriving theoretical boundaries of evaporative fraction (EF) and the concept of soil surface moisture availability isopleths was developed. It was applied to the Soil Moisture and Atmosphere Coupling Experiment (SMACEX) site in central Iowa, U.S., on three Landsat TM/ETM imagery acquisition dates in 2002. Results show the EF and latent heat flux (LE) estimates with a mean absolute percentage difference (MAPD) of 6.7 percent and 8.7 percent, respectively, relative to eddy covariance tower-based measurements after forcing closure by the Bowen ratio technique. (4) The domain and resolution dependencies of the Surface Energy Balance Algorithm for Land (SEBAL) and the triangle model were systematically investigated. Derivation of theoretical boundaries of EF for the two models could effectively constrain errors/uncertainties arising from these dependencies. (5) A Modified SEBAL (M-SEBAL) was consequently proposed, in which subjectivity involved in the selection of extreme pixels by the operator is eliminated. The performance of M-SEBAL at the SMACEX site is reasonably well, showing EF and LE estimates with an MAPD of 6.3 percent and 8.9 percent, respectively

Water availability and demand analysis in the Kabul River Basin, Afghanistan

Kabul River Basin (KRB), the most populated and highly heterogenic river basin of Afghanistan is the lifeline of millions of people in terms of supplying them with water for agricultural, municipal, and industrial as well as hydropower production purposes. Unfortunately, KRB is facing a multiplicity of governance, management and development relevant challenges for the last couple of decades. Detailed and reliable assessments of land use and land cover, water demand (for different sectors) as well as the available water resources are prerequisites for Integrated Water Resources Management across the basin. To achieve increased accuracy for water availability and demand analysis across the KRB, the study area was segregated into different hydrological and administrative units (provincial level, subbasin level etc.) in order to capture the heterogeneity driven by complex physiographic conditions (mainly due to huge elevation differences) and resulting in diverse cropping pattern at different reaches of the river basin. The innovative part of this study has been the concept of introducing spatial segregation of the large heterogenic river basin and using crop phenological information for evapotranspiration and land cover analysis respectively; it gave a distinct value to the output of this study. Phenologically tuned normalized difference vegetation indices (NDVI) of Aqua and Terra platforms with moderate resolution (250 m) proved to be very effective in the estimation of the land cover across the KRB with high accuracy. The phenology based segregated spatial analyses of the LULC of KRB with reference to 2003 (the base year of the study) highlighted the change in the ground coverage of main crops across the KRB e.g. wheat, barley, maize and rice. Based on the evaluation of the above results referring to the period 2003 to 2013, the rise in wheat ground coverage has been compensated by the decline in barley cultivation; maize and rice share has been almost consistent among the dominant cereals production in KRB. Upon spatial segregation, across the sub-basins (Alingar, Chak aw Logar, Ghorband aw Panjshir, Gomal, Kabul, Kunar and Shamal) Shamal, Kunar and Kabul showed highest actual evapotranspiration (ETa) throughout the study period of 2003 to 2013. The later three sub-basin host relatively large irrigated areas and production of two crops per year due to relatively favorable climatic and geographic conditions. Besides the agricultural water demand (ETa), water availability estimation through rainfall-runoff modelling by the use of the Soil and Water Assessment Tool (SWAT) has been very useful in data scarce regions like KRB. The application of the hydrological model using remote sensing products as input is the only effective choice in data scarce regions and exhibited results which are required by policy makers and investors for the strategic and sustainable planning and management of land and water resources

Influence of Morphology, Climate Change and Landuse Change on Water Partitioning in Olifants River Basin

Das Einzugsgebiet des Olifants River befindet sich derzeit in einer umfassenden Entwicklung der landwirtschaftlichen Landnutzungsaktivität. Trotz verschiedener Schutzpraktiken und Schutzmaßnahmen führt die Veränderung der Landnutzung immer noch zu einer Verschiebung im hydrologischen Regime. Als Treiber dieser rasanten Entwicklung in der Landnutzungsänderung durch landwirtschaftliche Nutzung sind der stetig steigende Nahrungsmittelbedarf und günstige klimatische Bedingung für die Landwirtschaft zu nennen. Ein stetiges Bevölkerungswachstum in Südafrika von etwa 1,4% pro Jahr weist auf eine kontinuierliche Nachfrage nach Nahrungsmitteln hin, die zu weiteren landwirtschaftlichen Expansionen und anschließend zu weiteren Veränderungen in der Hydrologie führen werden. Diese Situation könnte durch den Klimawandel und dadurch bedingte zunehmende Schwere extremer Phänomene wie Dürren und Überschwemmungen weiter verschärft werden. Diese Studie quantifiziert die Veränderungen des Klimas und der Landnutzung in den Teileinzugsgebieten Blyde River und Steelpoort River des Olifants Rivers, analysiert deren Einfluss auf die Hydrologie und schlägt eine Methode für die Landnutzungsplanung vor, mit der Änderungen im hydrologischen Regime abgemindert werden können. Historische Abflüsse, Temperatur und Niederschläge wurden mit statistischen Methoden ausgewertet, um das Vorhandensein von Veränderungen in den Zeitreihen für 37 Jahre ab dem Jahr 1980 festzustellen. 1996 und 2012 wurden zwei abrupte Veränderungen im Abflussgeschehen festgestellt. Diese Veränderungen wurden auf die hohe Häufigkeit extremer Niederschläge (> 40 mm / Tag) zwischen 1996 und 2012 zurückgeführt. Es wurde auch ein allmählicher Anstieg des Abflusses nachgewiesen, der jedoch nicht auf klimatische Faktoren zurückzuführen war. Darüber hinaus wurde ein allmählicher Temperaturanstieg festgestellt, der jedoch keinen nachweisbaren Einfluss auf die Evapotranspiration und andere hydrologische Faktoren hatte. Fernerkundliche Daten wurden zur Erkennung von Landnutzungsänderungen verwendet; vier Karten für 1992, 1998, 2002 und 2014 aus LANDSAT-Bildern. Die festgestellten signifikanten Veränderungen waren hauptsächlich auf die Urbanisierung und die landwirtschaftliche Entwicklung von etwa 169 km2 und 514 km2 zurückzuführen. Das SWAT-Modell wurde basierend auf dem LULC von 1992 kalibriert und zur Bewertung der Auswirkungen von Landnutzungsänderungen auf die Hydrologie verwendet. Basierend auf den LULC-Szenarien von 1992 und 2002 zeigten die Modellergebnisse eine Verringerung der Evapotranspiration um 6 mm, insbesondere in Gebieten, in denen Wälder durch Landwirtschaft ersetzt wurden, und eine allgemeine Erhöhung des Oberflächenabflusses um 3 mm, was auf die Verringerung der Oberflächenbedeckung zurückzuführen ist. Die weitere Ausdehnung des urbanen Bereichs und der Landwirtschaft zwischen 2002 und 2014 führte zu einer weiteren Erhöhung des Oberflächenabflusses um ca. 3 mm. Diese Studie schlägt einen Ansatz für die landwirtschaftliche Landnutzungsplanung vor, bei dem die Wechselwirkungen von Morphologie und Klima genutzt werden, um Gebiete zu identifizieren, die zu minimalen Auswirkungen auf die Landwirtschaft führen werden. Grünland wurde als Landnutzung identifiziert, die engere hydrologische Eigenschaften als die Landwirtschaft aufwies. Das Grünland wurde als LULC-Klasse ausgewählt, die durch Landwirtschaft ersetzt werden kann. Morphologische Analysen zeigten, dass eine geringe Hangneigung, eine höhere Bodenschüttdichte und eine geringe Robustheit des Geländes die besten physikalischen Bedingungen für die landwirtschaftliche Praxis sind. Dies würde jedoch zu einem Verlust der Vegetationsvielfalt bei anhaltender landwirtschaftlicher Expansion führen. Daher sollte das Ausmaß der Umwidmung von Grünland auf Landwirtschaft begrenzt werden und es sollten zusätzliche Studien zu den Auswirkungen dieser Methode auf die biologische Vielfalt durchgeführt werden

SWAT model application to estimate runoff for ungauged arid catchments experiencing rapid urbanisation: Riyadh case study

The built-up area of Riyadh city increased from approximately 4.5 km² in 1950 to reach approximately 1,600 km² by 2022 spreading over vast areas of the Wadi Hanifah and Wadi As Silayy catchments. The rapid growth of the city has led to repeated urban flooding. There is an urgent need to study surface runoff and how it is affected by land-use/land-cover (LULC) change in the ungauged catchments of the city. This study addressed that knowledge gap and was the first attempt to calibrate, validate, and run a semi-distributed model to simulate runoff depths and discharge rates for Riyadh's main catchments and sub-basins using five historical and five future scenarios. The Soil Water Assessment Tool (SWAT) was used for the modelling. TerraClimate evapotranspiration (ET) data was used to calibrate the SWAT model owing to a dearth of observed runoff data across Riyadh city. The literature review revealed that the use of Terraclimate ET to calibrate SWAT models is still very limited so far. The only previous study found is Herman et al. (2020). Therefore, this study is fairly unique in that it uses Terraclimate ET to successfully calibrate and validate a SWAT model. A one-by-one sensitivity analysis was performed to evaluate the impact of changing parameter values on the runoff simulations. The results indicated that simulated runoff sensitivity to selected parameter values in the calibrated SWAT models was minimal in the study area, where the relationships between simulated annual runoff and max and min runoff resulted in a very strong R2 (0.9998). The calibrated and validated SWAT models were run monthly and daily to simulate runoff and to assess the impact of several LULC change scenarios on surface runoff for both historical and future periods. The results of SWAT models of the main catchments and sub-basins located within the built-up areas demonstrated the positive effect of Riyadh’s development on runoff and discharge values for historical LULC scenarios and LULC 2030 probabilities scenarios. But the increasing rates of simulated runoff were not the same for all sub-basins due to the different proportions of urbanisation in each sub-basin. On the contrary, simulation results showed that runoff depths and discharge rates in sub-basins outside the boundaries of the built-up areas of Riyadh did not have significant changes when using historical LULC scenarios or LULC 2030 probabilities scenarios. The increase in runoff depths and discharge rates in the sub-basins reflected the direct influence of the urbanisation process on surface runoff. The increase in simulated surface runoff and discharge can be attributed mainly to the potential decrease of relatively permeable barren lands and the increase of impervious urban surfaces. Limitations faced during the SWAT model development suggest further research should aim to get detailed and accurate runoff estimates in Riyadh city to sufficiently assist decision-makers and city officials to adopt runoff and flood hazard management schemes in the city

SWAT model application to estimate runoff for ungauged arid catchments experiencing rapid urbanisation: Riyadh case study

The built-up area of Riyadh city increased from approximately 4.5 km² in 1950 to reach approximately 1,600 km² by 2022 spreading over vast areas of the Wadi Hanifah and Wadi As Silayy catchments. The rapid growth of the city has led to repeated urban flooding. There is an urgent need to study surface runoff and how it is affected by land-use/land-cover (LULC) change in the ungauged catchments of the city. This study addressed that knowledge gap and was the first attempt to calibrate, validate, and run a semi-distributed model to simulate runoff depths and discharge rates for Riyadh's main catchments and sub-basins using five historical and five future scenarios. The Soil Water Assessment Tool (SWAT) was used for the modelling. TerraClimate evapotranspiration (ET) data was used to calibrate the SWAT model owing to a dearth of observed runoff data across Riyadh city. The literature review revealed that the use of Terraclimate ET to calibrate SWAT models is still very limited so far. The only previous study found is Herman et al. (2020). Therefore, this study is fairly unique in that it uses Terraclimate ET to successfully calibrate and validate a SWAT model. A one-by-one sensitivity analysis was performed to evaluate the impact of changing parameter values on the runoff simulations. The results indicated that simulated runoff sensitivity to selected parameter values in the calibrated SWAT models was minimal in the study area, where the relationships between simulated annual runoff and max and min runoff resulted in a very strong R2 (0.9998). The calibrated and validated SWAT models were run monthly and daily to simulate runoff and to assess the impact of several LULC change scenarios on surface runoff for both historical and future periods. The results of SWAT models of the main catchments and sub-basins located within the built-up areas demonstrated the positive effect of Riyadh’s development on runoff and discharge values for historical LULC scenarios and LULC 2030 probabilities scenarios. But the increasing rates of simulated runoff were not the same for all sub-basins due to the different proportions of urbanisation in each sub-basin. On the contrary, simulation results showed that runoff depths and discharge rates in sub-basins outside the boundaries of the built-up areas of Riyadh did not have significant changes when using historical LULC scenarios or LULC 2030 probabilities scenarios. The increase in runoff depths and discharge rates in the sub-basins reflected the direct influence of the urbanisation process on surface runoff. The increase in simulated surface runoff and discharge can be attributed mainly to the potential decrease of relatively permeable barren lands and the increase of impervious urban surfaces. Limitations faced during the SWAT model development suggest further research should aim to get detailed and accurate runoff estimates in Riyadh city to sufficiently assist decision-makers and city officials to adopt runoff and flood hazard management schemes in the city

Is there a solution to the spatial scale mismatch between ecological processes and agricultural management?

The major limit to develop robust landscape planning for biodiversity conservation is that the spatial levels of organization of landscape management by local actors rarely match with those of ecological processes. This problem, known as spatial scale mismatch, is recognized as a reason of lack of effectiveness of agri-environment schemes. We did a review to describe how authors identify the problem of spatial scale mismatch in the literature. The assumption is made that the solutions proposed in literature to conciliate agricultural management and conservation of biodiversity are based on theoretical frameworks that can be used to go towards an integration of management processes and ecological processes. Hierarchy Theory and Landscape Ecology are explicitly mobilized by authors who suggest multiscale and landscape scale approaches, respectively, to overcome the mismatch problem. Coordination in management is proposed by some authors but with no theoretical background explicitly mentioned. The theory of organization of biological systems and the theories of Social-Ecological Systems use the concept of coordination and integration as well as concepts of organization, adaptive capabilities and complexity of systems. These theories are useful to set up a new framework integrating ecological processes and agricultural management. Based on this review we made two hypotheses to explain difficulties to deal with spatial scale mismatch: (1) authors generally do not have an integrated approach since they consider separately ecological and management processes, and (2) an inaccurate use of terminology and theoretical frameworks partially explain the inadequacy of proposed solutions. We then specify some terms and highlight some ‘rules’ necessary to set up an integrative theoretical and methodological framework to deal with spatial scale mismatch.(Presentation des résumés n°186, p. 95-96, non paginé

Integrated Water Resources Research

Anthropogenic and natural disturbances to freshwater quantity and quality are a greater issue for society than ever before. To successfully restore water resources requires understanding the interactions between hydrology, climate, land use, water quality, ecology, and social and economic pressures. This Special Issue of Water includes cutting edge research broadly addressing investigative areas related to experimental study designs and modeling, freshwater pollutants of concern, and human dimensions of water use and management. Results demonstrate the immense, globally transferable value of the experimental watershed approach, the relevance and critical importance of current integrated studies of pollutants of concern, and the imperative to include human sociological and economic processes in water resources investigations. In spite of the latest progress, as demonstrated in this Special Issue, managers remain insufficiently informed to make the best water resource decisions amidst combined influences of land use change, rapid ongoing human population growth, and changing environmental conditions. There is, thus, a persistent need for further advancements in integrated and interdisciplinary research to improve the scientific understanding, management, and future sustainability of water resources

The past : a compass for future earth

Antarctic sea ice impacts on the ocean-atmosphere heat and gas fluxes, the formation of deep and intermediate waters, the nutrient distribution and primary productivity, the so-called &#8216;biological carbon pump&#8217;, one of the most active in the global ocean. In this study, we explore the link between sea ice dynamic, biological production and nutrient cycling during the late Holocene (the last 2,000 yrs) in the Adélie Basin, East Antarctica, from the well-dated sediments of the Ocean Drilling Program (ODP) Site U1357. This archive, composed from ~32 meters of seasonal to annual laminated diatomaceous sequences, allows reconstructions at an unprecedented time resolution (5-10 yrs). Our study combines records of diatom census counts and diatom-specific biomarkers (a ratio (D/T) of di- and tri-unsaturated Highly Branched Isoprenoid lipids (HBI)) as indicators of sea ice and biological production changes, XRF data as markers for terrigenous inputs and bulk nitrogen isotopes (d15N) and d15N on chlorins as proxies for reconstructing nitrogen cycle. The diatom and HBI records reveal five distinct periods. From 0 to 350 yrs AD, decreasing occurrences of sea ice-related diatom species (e.g. Fragilariopsis curta + F. cylindrus) together with low D/T values and increasing open ocean diatom species (large centrics, Chaetoceros Resting Spores (CRS)) document a progressive decline of sea ice presence during the year (>9 months per year) with spring melting occurring earlier in the year and autumn sea ice formation appearing later. In contrast, between 350 and 750 yrs AD, high production of open ocean diatom species and low low D/T values and sea ice related species indicate a short duration of sea ice cover (~10 months per year) is illustrated by a pronounced increase of sea ice-associated diatom species and high D/T values. Between ~1400 and 1850 yrs AD, seasonal sea ice strongly declines (<~7 months per year) as a result of early spring melting (increasing CRS production) and late autumn waxing (high occurrences of Thalassiosira antarctica). Longer growing seasons promoted a substantial development of phytoplankton communities (especially large centric diatoms) that conducted to lower D/T values. Consistent with diatom and HBI reconstructions, XRF data show higher Fe/Al and Zr/Al ratios values during inferred warmer periods and lower ratio values during inferred cooler and icier periods, thus supporting a strong impact of the sea ice seasonal cycle on glacial runoffs. The link between sea ice conditions, biological production and nutrient cycling is still being explored and we will discuss its relationship by combining all the cited records cited above with the d15N records that we are currently generated. Based on our results, we find that sea ice dynamic and associated diatom production in the Adélie Basin revealed an opposite climatic trend than that identified in the Northern Hemisphere for the last 2000 years. The 'Little Ice Age' (1400-1850 yrs AD) or the 'Dark Ages' (400-750 yrs AD) corresponded to warmer climate conditions in the Adélie Basin, while the 'Roman Warm Period' (0-350 yrs AD) or the 'Medieval Warm Period' (900-1200 yrs AD) were associated to colder conditions. We therefore emphasize that Northern and Southern Hemisphere climate evolved in anti-phase seesaw pattern during the late Holocene