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Cardiff University (2021)

Modelling water partitioning in dryland regions : a multiscale analysis

Quichimbo Miguitama, Edisson

Titre : Modelling water partitioning in dryland regions : a multiscale analysis

Auteur : Quichimbo Miguitama, Edisson

Etablissement de soutenance : Cardiff University

Grade : Doctor of Philosophy (PhD) 2021

Dryland regions, characterised by naturally limited water availability, cover around 40% of the global land surface and sustain a vast population of around 2.1 billion people. These environments pose many challenges for water resources allocation for humans and water availability to ecology, yet there are currently major limitations in our ability to assess the dryland water balance, especially under a changing climate. Therefore, understanding and quantifying the mechanisms that control the water balance in dryland regions is of key importance not only to improve the management of limited water resources, but also to understand the future impacts of climate change in their spatial and temporal variability. Here, a series of numerical models at different temporal and spatial scales were developed to characterize and quantify the main mechanisms that control the water partitioning and flow pathways in dryland regions. First, by using physically-based numerical models which are able to describe the complexity of groundwater - surface water interactions, the analysis focused on the characterization of the infiltration of water through the streambed of ephemeral streams. Focused groundwater recharge, sourced from such transmission losses, is a mechanism that has received little attention in the literature due to the highly dynamic characteristics of this process and the scarcity of data required for a proper evaluation. Second, a novel, parsimonious, hydrologic model of DRYland water Partitioning (DRYP), has been developed to quantify the water partitioning in data scarce regions. The performance of DRYP was firstly evaluated by using synthetic experiments, and then it was tested in the data-rich Walnut Gulch Experimental Watershed, Arizona, US. It was finally applied in the semi-arid Upper Ewaso Ng’iro basin, Kenya, an area with limited data availability. Results of this study show that groundwater - surface water interactions play an important role in water partitioning in drylands, and need to be included in models in order to reduce the uncertainty of water balance quantification of these regions. The spatial and temporal variation in model process description as well as forcing variables also have a great impact on dryland water partitioning. A high spatial (≤1 km) and temporal (<1 d) resolution is required to adequately represent the development and subsurface interactions of ephemeral streams. Although highly uncertain, global datasets of climatological data, as well as regional and global datasets of surface and subsurface parameters, used in the parsimonious model DRYP can provide useful spatially and temporally information to quantify water partitioning in data scarce-regions. This study also highlights the importance of recharge from ephemeral streams in the water balance of dryland regions, a recharge mechanism that can become dominant as the aridity increases.


Page publiée le 1er décembre 2022