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1. Top-Down Approach for Time-Variant Anthropogenic Signature Attribution in Socio-Hydrological Systems

   Mohajer Iravanloo, B.; Garcia, M.; Sivapalan, M (December 2020, American Geophysical Union)

   In the Anthropocene, humans have altered the properties and processes of hydrological systems across scales. The extent of human intervention in the landscape limits the utility of traditional hydrological modelling schemes. Since purely hydrological conceptual models no longer fit these systems, hydrologists must integrate key human interventions into conceptual models of human-modified catchments. Despite the advances in analyzing the observed changes within the hydrological cycle using bottom-up (or reductionist) modelling approaches, the aptitude of top-down hydrologic schemes for socio-hydrological system analysis is still untested. Here we show the potential of top-down hydrological modelling human modified watersheds using anthropogenic hydrological signatures. Specifically, we assess the ability of the top-down modelling method in human-modified catchments to improve the representation hydrological signatures (e.g. mean monthly runoff, flow duration curve) while ensuring a sufficient, but not excessive, level of complexity in model formulation. First, we develop new conceptual models which include human hydrological modifications commonly identified in the literature. Then, we link these new features in the conceptual models to features in the hydrological signatures. We apply the proposed methodology to the Lake Mendocino Watershed in Northern California, US. We compare a purely hydrological model developed for this catchment based on natural watershed properties using naturalized streamflow to a hydrological model of the human-modified catchment using observed streamflow. We anticipate that the proposed approach contributes to the development of detection and attribution frameworks for key anthropogenic changes of observed hydrological variability and improved model performance in human-modified catchments. 

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2. DRYP 1.0: a parsimonious hydrological model of DRYland Partitioning of the water balance

   https://doi.org/10.5194/gmd-14-6893-2021  

   Quichimbo, E. Andrés; Singer, Michael Bliss; Michaelides, Katerina; Hobley, Daniel E.; Rosolem, Rafael; Cuthbert, Mark O. (January 2021, Geoscientific Model Development)

   Abstract. Dryland regions are characterised by water scarcity and are facingmajor challenges under climate change. One difficulty is anticipating howrainfall will be partitioned into evaporative losses, groundwater, soilmoisture, and runoff (the water balance) in the future, which has importantimplications for water resources and dryland ecosystems. However, in orderto effectively estimate the water balance, hydrological models in drylandsneed to capture the key processes at the appropriate spatio-temporal scales.These include spatially restricted and temporally brief rainfall, highevaporation rates, transmission losses, and focused groundwater recharge.Lack of available input and evaluation data and the high computational costsof explicit representation of ephemeral surface–groundwater interactionsrestrict the usefulness of most hydrological models in these environments.Therefore, here we have developed a parsimonious distributed hydrologicalmodel for DRYland Partitioning (DRYP). The DRYP model incorporates the keyprocesses of water partitioning in dryland regions with limited datarequirements, and we tested it in the data-rich Walnut Gulch ExperimentalWatershed against measurements of streamflow, soil moisture, andevapotranspiration. Overall, DRYP showed skill in quantifying the maincomponents of the dryland water balance including monthly observations ofstreamflow (Nash–Sutcliffe efficiency, NSE, ∼ 0.7),evapotranspiration (NSE > 0.6), and soil moisture (NSE ∼ 0.7). The model showed that evapotranspiration consumes > 90 % of the total precipitation input to the catchment andthat < 1 % leaves the catchment as streamflow. Greater than 90 % of the overland flow generated in the catchment is lost throughephemeral channels as transmission losses. However, only ∼ 35 % of the total transmission losses percolate to the groundwater aquiferas focused groundwater recharge, whereas the rest is lost to the atmosphereas riparian evapotranspiration. Overall, DRYP is a modular, versatile, andparsimonious Python-based model which can be used to anticipate and plan forclimatic and anthropogenic changes to water fluxes and storage in drylandregions. 

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3. Ecohydrologic separation alters interpreted hydrologic stores and fluxes in a headwater mountain catchment

   https://doi.org/10.1002/hyp.13518  

   Cain, Molly R.; Ward, Adam S.; Hrachowitz, Markus (August 2019, Hydrological Processes)

   Abstract Recent studies have demonstrated that compartmentalized pools of water preferentially supply either plant transpiration (poorly mobile water) or streamflow and groundwater (highly mobile water) in some catchments, a phenomenon referred to as ecohydrologic separation. The omission of processes accounting for ecohydrologic separation in standard applications of hydrological models is expected to influence estimates of water residence times and plant water availability. However, few studies have tested this expectation or investigated how ecohydrologic separation alters interpretations of stores and fluxes of water within a catchment. In this study, we compare two rainfall‐runoff models that integrate catchment‐scale representations of transport, one that incorporates ecohydrologic separation and one that does not. The models were developed for a second‐order watershed at the H.J. Andrews Experimental Forest (Oregon, USA), the site where ecohydrologic separation was first observed, and calibrated against multiple years of stream discharge and chloride concentration. Model structural variations caused mixed results for differences in calibrated parameters and differences in storage between reservoirs. However, large differences in catchment storage volumes and fluxes arise when considering only mobile water. These changes influence interpreted residence times for streamflow‐generating water, demonstrating the importance of ecohydrologic separation in catchment‐scale water and solute transport. 

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4. Modeled Streamflow Response to Scenarios of Tundra Lake Water Withdrawal and Seasonal Climate Extremes, Arctic Coastal Plain, Alaska

   https://doi.org/10.1029/2022WR032119  

   Gädeke, Anne; Arp, Christopher D.; Liljedahl, Anna K.; Daanen, Ronald P.; Cai, Lei; Alexeev, Vladimir A.; Jones, Benjamin M.; Wipfli, Mark S.; Schulla, Jörg (August 2022, Water Resources Research)

   Abstract On the Arctic Coastal Plain (ACP) in northern Alaska (USA), permafrost and abundant surface‐water storage define watershed hydrological processes. In the last decades, the ACP landscape experienced extreme climate events and increased lake water withdrawal (LWW) for infrastructure construction, primarily ice roads and industrial operations. However, their potential (combined) effects on streamflow are relatively underexplored. Here, we applied the process‐based, spatially distributed hydrological and thermal Water Balance Simulation Model (10 m spatial resolution) to the 30 km²Crea Creek watershed located on the ACP. The impacts of documented seasonal climate extremes and LWW were evaluated on seasonal runoff (May–August), including minimum 7‐day mean flow (MQ7), the recovery time of MQ7 to pre‐perturbation conditions, and the duration of streamflow conditions that prevents fish passage. Low‐rainfall scenarios (21% of normal, one to three summers in a row) caused a larger reduction in MQ7 (−56% to −69%) than LWW alone (−44% to −58%). Decadal‐long consecutive LWW under average climate conditions resulted in a new equilibrium in low flow and seasonal runoff after 3 years that included a disconnected stream network, a reduced watershed contributing area (54% of total watershed area), and limited fish passage of 20 days (vs. 6 days under control conditions) throughout summer. Our results highlight that, even under current average climatic conditions, LWW is not offset by same‐year snowmelt as currently assumed in land management regulations. Effective land management would therefore benefit from considering the combined impact of climate change and industrial LWWs. 

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5. From Patch to Catchment: A Statistical Framework to Identify and Map Soil Moisture Patterns Across Complex Alpine Terrain

   https://doi.org/10.3389/frwa.2020.578602  

   Hermes, Anna L.; Wainwright, Haruko M.; Wigmore, Oliver; Falco, Nicola; Molotch, Noah P.; Hinckley, Eve-Lyn S. (November 2020, Frontiers in Water)

   Climate warming in alpine regions is changing patterns of water storage, a primary control on alpine plant ecology, biogeochemistry, and water supplies to lower elevations. There is an outstanding need to determine how the interacting drivers of precipitation and the critical zone (CZ) dictate the spatial pattern and time evolution of soil water storage. In this study, we developed an analytical framework that combines intensive hydrologic measurements and extensive remotely-sensed observations with statistical modeling to identify areas with similar temporal trends in soil water storage within, and predict their relationships across, a 0.26 km 2 alpine catchment in the Colorado Rocky Mountains, U.S.A. Repeat measurements of soil moisture were used to drive an unsupervised clustering algorithm, which identified six unique groups of locations ranging from predominantly dry to persistently very wet within the catchment. We then explored relationships between these hydrologic groups and multiple CZ-related indices, including snow depth, plant productivity, macro- (10 2 ->10 3 m) and microtopography (<10 0 -10 2 m), and hydrological flow paths. Finally, we used a supervised machine learning random forest algorithm to map each of the six hydrologic groups across the catchment based on distributed CZ properties and evaluated their aggregate relationships at the catchment scale. Our analysis indicated that ~40–50% of the catchment is hydrologically connected to the stream channel, lending insight into the portions of the catchment that likely dominate stream water and solute fluxes. This research expands our understanding of patch-to-catchment-scale physical controls on hydrologic and biogeochemical processes, as well as their relationships across space and time, which will inform predictive models aimed at determining future changes to alpine ecosystems. 

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