416 research outputs found

    Flood dynamics derived from video remote sensing

    Get PDF
    Flooding is by far the most pervasive natural hazard, with the human impacts of floods expected to worsen in the coming decades due to climate change. Hydraulic models are a key tool for understanding flood dynamics and play a pivotal role in unravelling the processes that occur during a flood event, including inundation flow patterns and velocities. In the realm of river basin dynamics, video remote sensing is emerging as a transformative tool that can offer insights into flow dynamics and thus, together with other remotely sensed data, has the potential to be deployed to estimate discharge. Moreover, the integration of video remote sensing data with hydraulic models offers a pivotal opportunity to enhance the predictive capacity of these models. Hydraulic models are traditionally built with accurate terrain, flow and bathymetric data and are often calibrated and validated using observed data to obtain meaningful and actionable model predictions. Data for accurately calibrating and validating hydraulic models are not always available, leaving the assessment of the predictive capabilities of some models deployed in flood risk management in question. Recent advances in remote sensing have heralded the availability of vast video datasets of high resolution. The parallel evolution of computing capabilities, coupled with advancements in artificial intelligence are enabling the processing of data at unprecedented scales and complexities, allowing us to glean meaningful insights into datasets that can be integrated with hydraulic models. The aims of the research presented in this thesis were twofold. The first aim was to evaluate and explore the potential applications of video from air- and space-borne platforms to comprehensively calibrate and validate two-dimensional hydraulic models. The second aim was to estimate river discharge using satellite video combined with high resolution topographic data. In the first of three empirical chapters, non-intrusive image velocimetry techniques were employed to estimate river surface velocities in a rural catchment. For the first time, a 2D hydraulicvmodel was fully calibrated and validated using velocities derived from Unpiloted Aerial Vehicle (UAV) image velocimetry approaches. This highlighted the value of these data in mitigating the limitations associated with traditional data sources used in parameterizing two-dimensional hydraulic models. This finding inspired the subsequent chapter where river surface velocities, derived using Large Scale Particle Image Velocimetry (LSPIV), and flood extents, derived using deep neural network-based segmentation, were extracted from satellite video and used to rigorously assess the skill of a two-dimensional hydraulic model. Harnessing the ability of deep neural networks to learn complex features and deliver accurate and contextually informed flood segmentation, the potential value of satellite video for validating two dimensional hydraulic model simulations is exhibited. In the final empirical chapter, the convergence of satellite video imagery and high-resolution topographical data bridges the gap between visual observations and quantitative measurements by enabling the direct extraction of velocities from video imagery, which is used to estimate river discharge. Overall, this thesis demonstrates the significant potential of emerging video-based remote sensing datasets and offers approaches for integrating these data into hydraulic modelling and discharge estimation practice. The incorporation of LSPIV techniques into flood modelling workflows signifies a methodological progression, especially in areas lacking robust data collection infrastructure. Satellite video remote sensing heralds a major step forward in our ability to observe river dynamics in real time, with potentially significant implications in the domain of flood modelling science

    Regional water balance analysis of glacierised river basins in the north-eastern Himalaya applying the J2000 hydrological model

    Get PDF
    The glacierised basins of the Northeast Himalayan region are highly vulnerable to climate-change impacts. The spatio-temporal hydroclimatic and physiographic variability impact the water balance of these glacierised basins across the region. This study assesses the glaciohydrological processes and dynamics in the data scarce region for the present as well future climate change scenarios by regional water balance analysis. The J2000 hydrological model was adapted to incorporate the frozen ground as well as glacier dynamics in a stepwise, nested basin calibration approach. The modelled ERA-Interim precipitation data cannot capture the high amplitude orographic and convective events. Therefore, Orographic correction factors were used to inversely correct the ERA-Interim precipitation data to account for the orographic as well as cyclonic precipitation in the region from reported glacier mass balance and evapotranspiration estimates. Monthly temperature lapse rate was adopted for correcting the ERA-Interim temperature dataset. The Beki basin was selected as the donor basin for model development and evaluation. The parameters from the Beki basin were regionalised to the receptor Lohit and the Noadihing basins by the Proxy-basin method. Multi-objective optimization criteria such as the Kling-Gupta efficiency (KGE) for temporal dynamics and flow distribution and Bias for overall water balance showed high to moderate conformity between measured and simulated discharge at the corresponding basin outlets. The variability in the water balance and runoff components among the three basins was primarily related to the spatio-temporal variation in the mean annual precipitation, runoff and evapotranspiration estimates. The impact of climate-change scenarios on the study basins indicated that water availability would sustain until the end of the century due to higher projected precipitation even though after the depletion of glaciers in the region

    Understanding the Lowermost Stratosphere in Current and Future Climates: Composition, Definition, and Tropopause-Overshooting Convection

    Get PDF
    The troposphere and the stratosphere are two separate layers of the atmosphere whose dynamics, composition, and chemistry are fundamentally different. This leads to the upper troposphere and lower stratosphere (UTLS) being a complex region of the atmosphere that is critically important to both weather and climate. The upper troposphere is separated from the lower stratosphere by an identified ‘tropopause’, and any transfer of air across this interface is therefore considered to be stratosphere- troposphere exchange (STE). The difference in composition between the troposphere and the stratosphere makes processes that facilitate STE essential to the climate system. Specifically, the transport of water vapor from the relatively moist troposphere to the much drier lower stratosphere, where water vapor functions as a powerful greenhouse gas, can contribute substantially to the warming climate at the surface. The sources of stratospheric water vapor are still a topic of debate in the scientific community, where the specific contributions of larger-scale processes like the global atmospheric circulation and smaller-scale processes like tropopause-overshooting convection remain unclear, though recent evidence has demonstrated the latter to be more important than was previously thought. This dissertation seeks to clarify the role that tropopause-overshooting convection has in modulating the lower stratospheric water vapor budget in both the present and in the future. The first component of this dissertation is the creation of a climatology of extreme water vapor concentrations within the lowermost stratosphere, with a complementary analysis exploring the sources and transport pathways of these extreme concentrations. Stratospheric water vapor is a substantial component of the global radiation budget, and therefore important to variability of the climate system. Efforts to understand the distribution, transport, and sources of stratospheric water vapor have increased in recent years, with many studies utilizing long-term satellite observations. Previous work to examine stratospheric water vapor extrema has typically focused on the stratospheric overworld (pressures ≤ 100 hPa) to ensure the observations used are truly stratospheric. However, this leads to the broad exclusion of the lowermost stratosphere, which can extend over depths more than 5 km below the 100 hPa level in the midlatitudes and polar regions and has been shown to be the largest contributing layer to the stratospheric water vapor feedback. Moreover, focusing on the overworld only can lead to a large underestimation of stratospheric water vapor extrema occurrence. Therefore, this dissertation expands on previous work by examining 16 years of Microwave Limb Sounder (MLS) observations of water vapor extrema (≥ 8 ppmv) in both the stratospheric overworld and the lowermost stratosphere to create a new lower stratosphere climatology. The resulting frequency of H2O extrema increases by more than 300% globally compared to extrema frequencies within stratospheric overworld observations only, though the percentage increase varies substantially by region and season. Additional context is provided to this climatology through a backward isentropic trajectory analysis to identify potential sources of the extrema. It is shown that, in general, tropopause-overshooting convection presents as a likely source of H2O extrema in much of the world, while meridional isentropic transport of air from the tropical upper troposphere to the extratropical lower stratosphere is also possible. The second dissertation component takes a step back to examine challenges related to definition of the tropopause. Any study which examines cross-tropopause transport, like the first component of this dissertation, is reliant on an accurately identified tropopause in order to correctly assess STE. Thus, proper definition of the tropopause has far reaching implications for our understanding of Earth’s radiation budget and climate. Definition of the tropopause has remained a focus of atmospheric science since its discovery near the beginning of the 20th century. Few universal definitions (those that can be reliably applied globally and to both common observations and numerical model output) exist and many definitions with unique limitations have been developed over the years. The most commonly used universal definition of the tropopause is the temperature lapse-rate definition established by the World Meteorological Organization (WMO) in 1957 (the LRT). Despite its widespread use, there are recurrent situations where the LRT definition fails to reliably identify the tropopause. Motivated by increased availability of coincident observations of stability and composition, this study seeks to re-examine the relationship between stability and composition change in the tropopause transition layer and identify areas for improvement in stability-based definition of the tropopause. In particular, long-term (40+ years) balloon observations of temperature, ozone, and water vapor from six locations across the globe are used to identify co-variability between several metrics of atmospheric stability and composition. The results demonstrate that the vertical gradient of potential temperature is a superior stability metric to identify the greatest composition change in the tropopause transition layer, which is used to propose a new universally applicable potential temperature gradient tropopause (PTGT) definition. Application of the new definition to both observations and reanalysis output reveals that the PTGT largely agrees with the LRT, but more reliably identifies tropopause-level composition change when the two definitions differ greatly. The final component of this dissertation examines the response of tropopause-overshooting convection to a warming climate. Recent field campaigns, observational studies, and modeling work, in addition to the first component of this dissertation, have demonstrated that extratropical tropopause-overshooting convection has a substantial, and previously underestimated impact on UTLS composition, especially stratospheric water vapor. This necessitates improved understanding of how tropopause-overshooting convection may change in a warming climate. A growing body of research indicates that environments conducive to severe thunderstorms will occur more often and be increasingly unstable in the future, but no study has examined how this may be related to increased overshooting. To rectify this, this study leverages an existing pseudo-global warming (PGW) experiment to evaluate potential future changes in tropopause-overshooting convection over North America. The PGW technique applies monthly, three-dimensional projected climate changes in state variables (temperature, humidity, wind, etc.) from global climate models to a weather and research forecasting (WRF) convection-allowing model simulation with a 4-km grid. Specifically, I examine two 10-year simulations consisting of (1) a retrospective period (2003 – 2012) forced by ERA-interim initial and boundary conditions (the control simulation), and (2) the same retrospective period with CMIP5 ensemble-mean high-end emission scenario climate changes added to the initial and boundary conditions (the PGW simulation). Tropopause-overshooting convection is identified as model cloud tops exceeding the potential temperature gradient tropopause, with overshooting in the control simulation validated against observed overshoots from both ground-based radar observations in the United States and GOES satellite observations over North America. The model is shown to effectively simulate the observed regional distribution, annual cycle, and diurnal cycle of tropopause-overshooting convection. The projected response of tropopause-overshooting convection in the PGW simulation is found to be a more than 250% increase across the model domain, and the projected seasonal period of frequent tropopause-overshooting convection was shown to extend into late-summer. Additionally, tropopause-overshooting convection with extreme tropopause-relative heights (> 4 km) are more frequent in a warmed climate scenario. In summary, this dissertation (1) examines extreme water vapor concentrations in the lowermost stratosphere and how they relate to tropopause-overshooting convection, (2) introduces an improved stability-based tropopause definition to improve future studies of stratosphere-troposphere exchange, and (3) investigates for the first time how tropopause-overshooting convection will respond to climate change

    Understanding daily precipitation over Monsoon and Southeast Asia in observations and regional climate models

    Full text link
    Monsoon Asia (MA) is the world’s most populous continent with high vulnerability to extreme weather, notably precipitation extremes. Due to sparse observations and limited modelling, past trends in extreme precipitation and future projections over many parts of the region are not well known. This thesis investigates regional precipitation (e.g., distribution, seasonality, variability, extremes, and past and future changes) over different sub-regions of MA using observations and climate models. The intercomparison of multiple observational precipitation products reveals the high temporal and spatial consistency in precipitation extremes in high-station density areas (e.g., Japan, India) and the large inter-product spread over limited-station regions (e.g., Southeast Asia - SEA). Products with high consistency in trends and variability for individual sub-regions of MA are selected to evaluate the performance of an ensemble of high-resolution regional climate models (RCMs) from the Coordinated Regional Downscaling Experiment (CORDEX). Rainfall patterns are investigated using various aspects of the precipitation distribution in CORDEX-SEA RCMs and compared with their forcing global climate models (GCMs). We find that RCMs are wetter and generally not as close to observations as their forcing GCMs. The more intense precipitation in RCMs is associated with 1) an increased supply of moisture from both local and large-scale sources and 2) a widespread increase in convective precipitation across the region. Our findings suggest that the RCM setup (e.g., parameterization scheme) is more important than the choice of GCM. Given the range of RCM performance, two sub-ensembles representing “better” and “worse” performing models are selected and their respective projections are compared to assess how past model performance can affect future projections. The thesis results highlight that careful model evaluation is needed and could lead to more well-informed future projections at the regional and seasonal scales relevant to the complex region of SEA. The framework and method developed in this thesis enable many avenues of research, such as understanding biases in regional and global models and how these could impact future projections. Ultimately, our understanding of regional rainfall patterns is improved, which in turn helps to better inform modelling strategies and the risks associated with future changes in precipitation under a warmer climate

    Towards COP27: The Water-Food-Energy Nexus in a Changing Climate in the Middle East and North Africa

    Get PDF
    Due to its low adaptability to climate change, the MENA region has become a "hot spot". Water scarcity, extreme heat, drought, and crop failure will worsen as the region becomes more urbanized and industrialized. Both water and food scarcity are made worse by civil wars, terrorism, and political and social unrest. It is unclear how climate change will affect the MENA water–food–energy nexus. All of these concerns need to be empirically evaluated and quantified for a full climate change assessment in the region. Policymakers in the MENA region need to be aware of this interconnection between population growth, rapid urbanization, food safety, climate change, and the global goal of lowering greenhouse gas emissions (as planned in COP27). Researchers from a wide range of disciplines have come together in this SI to investigate the connections between water, food, energy, and climate in the region. By assessing the impacts of climate change on hydrological processes, natural disasters, water supply, energy production and demand, and environmental impacts in the region, this SI will aid in implementation of sustainable solutions to these challenges across multiple spatial scales

    Examining Ecosystem Drought Responses Using Remote Sensing and Flux Tower Observations

    Get PDF
    Indiana University-Purdue University Indianapolis (IUPUI)Water is fundamental for plant growth, and vegetation response to water availability influences water, carbon, and energy exchanges between land and atmosphere. Vegetation plays the most active role in water and carbon cycle of various ecosystems. Therefore, comprehensive evaluation of drought impact on vegetation productivity will play a critical role for better understanding the global water cycle under future climate conditions. In-situ meteorological measurements and the eddy covariance flux tower network, which provide meteorological data, and estimates of ecosystem productivity and respiration are remarkable tools to assess the impacts of drought on ecosystem carbon and water cycles. In regions with limited in-situ observations, remote sensing can be a very useful tool to monitor ecosystem drought status since it provides continuous observations of relevant variables linked to ecosystem function and the hydrologic cycle. However, the detailed understanding of ecosystem responses to drought is still lacking and it is challenging to quantify the impacts of drought on ecosystem carbon balance and several factors hinder our explicit understanding of the complex drought impacts. This dissertation addressed drought monitoring, ecosystem drought responses, trends of vegetation water constraint based on in-situ metrological observations, flux tower and multi-sensor remote sensing observations. This dissertation first developed a new integrated drought index applicable across diverse climate regions based on in-situ meteorological observations and multi-sensor remote sensing data, and another integrated drought index applicable across diverse climate regions only based on multi-sensor remote sensing data. The dissertation also evaluated the applicability of new satellite dataset (e.g., solar induced fluorescence, SIF) for responding to meteorological drought. Results show that satellite SIF data could have the potential to reflect meteorological drought, but the application should be limited to dry regions. The work in this dissertation also accessed changes in water constraint on global vegetation productivity, and quantified different drought dimensions on ecosystem productivity and respiration. Results indicate that a significant increase in vegetation water constraint over the last 30 years. The results highlighted the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate

    Advanced Remote Sensing Precipitation Input for Improved Runoff Simulation : Local to regional scale modelling

    Get PDF
    Accurate precipitation data are crucial for hydrological modelling and rainwater runoff management. Precipitation variability exists through a wide range of spatial and temporal scales and cannot be captured well using sparse rain gauge networks. This limitation is further emphasised for urban and mountainous catchments, especially under global warming, causing an increased frequency of extreme events. Recent advances in remote sensing (RS) techniques make monitoring precipitation possible over larger areas at more regular resolutions than conventional rain gauge networks. The RS data can be biased mainly due to the indirect estimations prone to multiple error sources and temporally discrete observations. The wealth of spatiotemporal precipitation data by RS, however, calls for developing data-driven solutions for both the bias correction and hydrological modelling that, in turn, requires new procedures to assure generalization of the existing methods. The present dissertation comprises a comprehensive summary followed by five appended papers, attempting to evaluate quantitative precipitation estimations (QPE) by state-of-the-art instruments/products for local and regional hydrological applications. Accordingly, two recently installed dual polarimetric doppler X-band weather radars (X-WRs) in southern Sweden and multiple Global Precipitation Mission (GPM) products in Iran were studied at the relevant scales for urban hydrology (1–5-min and sub-km) and large water supply river–reservoir system operation (daily-monthly and 0.1°), respectively. The validation against rain gauge observations (Paper I and II) showed a significant dependency of the X-WR and GPM precipitation errors on the radial distance and regional precipitation pattern, respectively. Taking observations from local tipping bucket rain gauges at the 1–30-km ranges as a reference, the apparent problems with a single X-WR is related to the attenuation during heavy rains and overshooting (at higher elevation angle scans). An internationally bias-corrected GPM product called GPM-IMERG-Final shows a generally good correlation to synoptic observations of over 300 rain gauges in Iran except for extreme observations that are much better predicted by the GPM-IMERG Late product during spring, summer, and autumn seasons. To leverage the wealth of spatiotemporally complete and validated precipitation data for hydrological modelling, two novel data-driven procedures using artificial neural networks (ANNs) were developed. As in Paper III, the formulation of the new ANN input variables, namely, ECOVs and CCOVs, representing the event- and catchment-specific areal precipitation coverage ratios, improve monthly runoff estimations in all the studied sub-catchments of the Karkheh River basin (KRB) in the mountainous semi-arid climate of western Iran. Merging the doppler and dual-polarization data in the overlapping coverage of the two XWRs (Paper IV) via an ANN-based QPE improves rainfall detection and accuracy. ANN-assisted estimation of rainfall quantiles, compared to the merging with an empirically based regression model, also shows better results especially related to the extreme 5-min data. Finally, Paper V describes the impact of human activities such as agricultural developments that can equally affect the runoff variation. This fact is considered in Paper III by including MODIS Terra products as additional inputs

    Remote Sensing of Precipitation: Part II

    Get PDF
    Precipitation is a well-recognized pillar in the global water and energy balances. The accurate and timely understanding of its characteristics at the global, regional and local scales is indispensable for a clearer insight on the mechanisms underlying the Earth’s atmosphere-ocean complex system. Precipitation is one of the elements that is documented to be greatly affected by climate change. In its various forms, precipitation comprises the primary source of freshwater, which is vital for the sustainability of almost all human activities. Its socio-economic significance is fundamental in managing this natural resource effectively, in applications ranging from irrigation to industrial and household usage. Remote sensing of precipitation is pursued through a broad spectrum of continuously enriched and upgraded instrumentation, embracing sensors which can be ground-based (e.g., weather radars), satellite-borne (e.g., passive or active space-borne sensors), underwater (e.g., hydrophones), aerial, or ship-borne. This volume hosts original research contributions on several aspects of remote sensing of precipitation, including applications which embrace the use of remote sensing in tackling issues such as precipitation estimation, seasonal characteristics of precipitation and frequency analysis, assessment of satellite precipitation products, storm prediction, rain microphysics and microstructure, and the comparison of satellite and numerical weather prediction precipitation products

    Lower Atmosphere Meteorology

    Get PDF
    The Atmosphere Special Issue “Lower Atmosphere Meteorology” deals with the meteorological processes that occur in the layer of the atmosphere close to the surface. The interaction between the biosphere and the atmosphere is made through the lower layer and can greatly influence living beings and materials. The analysis of the meteorological parameters provides a better understanding of processes within the lower atmosphere and involved in air pollution, climate, and weather. The mixed layer height, the wind speed, and the air parcel trajectory have a relevant interest due to their marked impact on population and energy production. The research also comprises aerosols, clouds, and precipitation, analysing their spatiotemporal variations. This issue addresses features of gases in the atmosphere and anthropogenic greenhouse emission estimates, which are also conditioned by the lower atmosphere meteorology
    corecore