Compound drivers of hydroclimatic extremes in large river basins:Mapping future floods and water resources by modeling compound drivers at multiple spatial and temporal scales

Autor: Khanal, Sonu
Jazyk: angličtina
Rok vydání: 2021
Předmět:
Zdroj: Khanal, S 2021, ' Compound drivers of hydroclimatic extremes in large river basins : Mapping future floods and water resources by modeling compound drivers at multiple spatial and temporal scales ', Dr., Vrije Universiteit Amsterdam, Utrecht .
Popis: The societal and economic losses due to compound extremes, i.e., extreme events often result from one extreme state or amplification due to many other contributing mild or extreme states, are manifold higher in magnitude compared to the impacts of those from individual extremes alone. To understand the future impact of compound flood events at different spatio-temporal aggregation levels and climate zones, i.e., mountains, flood plains, and coasts, it is inevitable to examine the mechanisms of compound floods. To this end, this thesis highlights the importance of an integrated process-based physical modelling approach (atmospheric, hydrological and hydrodynamic) for the proper investigation of future flood risk. The research described in this thesis cover several relevant topics related to a complete flood risk chain (from mountains to coasts) and their impact on water resources in regions around the world (i.e., Europe and Asia). First part of this thesis focuses on empirical, univariate and bivariate approaches to understand historical climate trends and associated hazards in data scarce High Mountain Asia (HMA). This study provides a concise overiew of climate related changes across different regions which were difficult to align and compare either due to use of different data or spatio-temporal scales. Analysis reveals while the temperature is consistently increasing at a higher rate than the global warming rate, precipitation changes are not uniform, with substantial temporal and spatial variation in particular for the higher altitudes of HMA. Changes in climatic variables give rise to nonlinear, non-stationary, and non-uniform responses of cryospheric and hydrological variables such as snow, glaciers, soil moisture, and groundwater. Therefore, second part of this thesis investigates the systemic effect of the compound occurrence of extreme precipitation and temperature, at a wide range of spatio-temporal scales, and their impacts on the seasonality and trends in total water availability for HMA using a high-resolution cryospheric-hydrological model. This study shows a shift in the magnitude and peak of water availability, at seasonal time scale, to earlier in the year due to earlier onset of melting. Analysis reveals that the contrasting responses of HMA's rivers are primarily dictated by their hydrological regimes. To understand the risk due to compound floods in coastal regions, the third study of this thesis investigates the possibility of finding near-simultaneous storm surge and extreme river discharge along the Dutch coast using an extended dataset derived from a storm surge model and two hydrological river-discharge models forced with conditions from a high-resolution regional climate model in ensemble mode. This study conceptually shows that a strong storm whose winds set up a storm surge will need time to reach the Rhine headwaters where heavy rainfall will find its way to the river mouth after multiple days of travel time. The fourth and final study of this thesis investigates and quantifies the role of memory components in hydrological and meteorological systems which are responsible to generate extreme discharge, i.e. soil moisture, snow accumulation and the antecedent hydro-climatic conditions. Results show that the meteorological autocorrelation (manifesting itself by the occurrence of clustered precipitation events) has a strong impact on the magnitude of peak discharge. Finally, the study illustrates how hydrological memory from snow accumulation and soil moisture complements the generation of extreme discharges. A new valuable insight on the mechanisms of compound floods and its potential impact on water resources (both for historical and future climate) has been gained with novel modelling approaches. The outcomes generated from this thesis might contribute to support climate change adaptation policy planning and outreach programs in these climate change hotspots, i.e., the mountains and deltas.
Databáze: OpenAIRE
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