Hydrological Processes最新文献

Shallow groundwater in many cities around the world is subject to elevated temperatures that pose a risk to the groundwater quality and ecosystems. The objective of this study is to assess the suitability of different trend estimation methods for groundwater temperature and to specifically investigate the spatio-temporal long-term changes of water temperature in the urban groundwater of Vienna. Twenty-year data records (2001–2020) from different sources were used to assess changes in air, soil, river and groundwater temperature regarding their annual mean and extreme percentile values. The effects of data quality, different trend methods, and various time periods of analysis were investigated. Block bootstrapping in combination with the Mann–Kendall trend test was found to be a suitable method for determining the significance of mean trends if the time-series are short (10 years), as the underlying assumptions are lowest among all approaches. Between 2001 and 2020, the average annual temperature in Vienna increased by 0.9 K/decade for shallow groundwater and by 0.8 K/decade for air. However, the increase is not linear and has intensified in the later decade with an increase of 1.4 K/decade. The trends in extreme temperatures, represented by the lower (cold) / upper (warm) 10th percentile of air, soil and groundwater temperatures in the quantile regression, show the strongest increase in the lower 10th percentile of all air and soil temperatures. For groundwater, these extreme value trends are site-specific and influenced by urban infrastructure and the interaction of groundwater with river water. These results underline the importance of spatially and temporally high-resolution data and highlight the need for site-specific aquifer characterisation for the sustainable use of shallow geothermal energy for heating and cooling. The trend of GWT rise in the urban aquifer needs to be considered in water management to avoid possible negative consequences for water quality and ecology.

Urban green spaces (UGS) provide essential ecosystem services (ES), for example, precipitation infiltration for flood mitigation, transpiration (Tr) for local atmosphere cooling and groundwater recharge (Gr) for drinking water provision. However, vegetation type impacts the ecohydrological partitioning of incoming precipitation and therefore ES provision, whilst flux rate potential is different in disparate hydroclimates. Consequently, paired studies in different hydroclimates are useful to understand similarities and differences in vegetation controlled ecohydrological partitioning to effectively guide UGS management. We simultaneously undertook sub-daily soil moisture measurements beneath three contrasting urban vegetation types (grass, shrub, mature tree) between 01/01/2021 and 31/12/2023 for an inter-comparison of an energy-limited Scottish and a moisture-limited region of Germany. These data were integrated with hydroclimatic and sapflux data in the EcoHydroPlot model to constrain estimates of ecohydrological fluxes. Soil moisture data showed clear effects of the contrasting hydroclimates, with high and low VWC values in Scotland and Germany, respectively, whilst evapotranspiration potential was ~50% greater in Germany. Consequently, ecohydrological functioning and flux rates were fundamentally different, with Tr dominant in Germany and Gr dominant in Scotland. However, vegetation cover was shown in both countries to be a key control on urban ecohydrological partitioning with grass encouraging Gr, contrasting to evergreen shrubs in Scotland and mature trees in Germany elevating Tr. In Germany, impacts to hydrological functioning due to low soil VWC were marked with the mature trees high Tr rate shutting down Gr for the majority of the study period. The German site also showed greater hydrological functioning susceptibility to inter-annual hydroclimatic variability with all fluxes heavily suppressed during the 2022 drought. In contrast, the high VWC in Scotland provided some buffer against ongoing negative rainfall anomalies. Overall, the study indicated the importance of diverse UGS vegetation cover to encourage contrasting ecohydrological fluxes.

Coastal water temperatures control physical, chemical, and biological processes and are expected to rise due to future changes in freshwater temperature and flow rates, heat exchange with the warming atmosphere, and thermal interactions with a changing ocean. However, the thermal sensitivity of transitional, coastal water bodies to climate change remains poorly understood, due partly to a lack of knowledge on present-day thermal controls in these settings. Accordingly, we applied a coastal hydrodynamic model (MIKE 3 FM), with a coupled thermal module to simulate hydrodynamics and water temperature variability in the Basin Head lagoon, a federally protected coastal ecosystem in the Canadian province of Prince Edward Island. Field data from the lagoon were used to calibrate and assess the numerical model, while atmospheric, oceanic, and hydrologic data were used to form the thermal and hydrodynamic boundary conditions. The model successfully reproduced tidal water level oscillations as well as diurnal and semi-diurnal (tidal) temperature fluctuations. Model results show longitudinal, cross-shore, and vertical thermal variability within the lagoon, including pronounced thermal variability near the bed and near the inlet due to tidal pumping. Model results and field data highlight the thermal sensitivity of the lagoon during heat waves; however, distinct cold-water plumes at freshwater inputs (springs and groundwater-dominated streams) persisted, with temporally averaged temperatures in these zones up to 18 °C colder than the ambient lagoon. Although, these freshwater inflows can dominate local energy budgets, the surface heat fluxes, especially shortwave radiation, exert the dominant control on the lagoon-wide energy budget. Collectively, the model findings emphasise the interacting effects of atmospheric, hydrologic, and oceanic forcing on the spatiotemporal patterns of water temperatures in this threatened coastal ecosystem.

The Bowen ratio, defined as the ratio of sensible to latent heat flux, is crucial for quantifying land-atmosphere energy exchanges and evaporation rates from terrestrial surfaces. Despite extensive research on the Bowen ratio over placid water surfaces (e.g., lakes), further investigation is needed to understand its dynamics in small reservoirs subjected to water inflow/outflow (i.e., surface flows) and wind. To address this knowledge gap, the evaporation rate and the sensible heat exchanges are measured between the water surface and overlying air in a small laboratory basin under different water surface flow rates (1.0–10.5 l min⁻¹) and wind speeds (0–2.0 m s⁻¹). Three different wind flow conditions are explored: no wind, headwind (opposing the water surface flow), and tailwind (aligning with water surface flow). The findings indicate strong correlations between sensible heat flux, water surface flow rate, and wind speed, particularly under headwind conditions. Nevertheless, concerning the latent heat flux, the measurements demonstrate that for each wind condition, the evaporation reaches its minimum value in a certain water surface flow rate, resulting in the highest value of the Bowen ratio. To facilitate the application of these laboratory findings for estimating the Bowen ratio under real environmental conditions, mathematical relationships using dimensionless numbers obtained through non-linear regression analysis are established. The results exhibit a good agreement with measurements in a small water basin.

Increasing drought frequency and severity from climate change are causing streamflow to become increasingly intermittent in many areas. This has implications for the spatio-temporal characteristics of water quality regimes which need to be understood in terms of risks to the provision of clean water for public supplies and instream habitats. Recent advances in sensor technology allow reliable and accurate high-resolution monitoring of a growing number of water quality parameters. Here, we continuously monitored a suite of water quality parameters over 3 years in an intermittent stream network in the eutrophic, lowland Demnitzer Millcreek catchment, Germany. We focused on the effects of wetland systems impacted by beaver dams on the diurnal, seasonal and inter-annual variation in water quality dynamics at two sites, upstream and downstream of these wetlands. We then used the data to model stream metabolism. Dissolved oxygen and pH were higher upstream of the wetlands, while conductivity, turbidity, chlorophyll a and phosphorous concentrations were higher downstream. We found clear diurnal cycling of dissolved oxygen and pH at both sites. These dynamics were correlated with seasonal hydroclimatic changes and stream metabolism, becoming increasingly pronounced as temperatures increased and flows decreased in spring and summer. Upstream of the wetlands this corresponded to the stream rapidly becoming increasingly heterotrophic as modelled Gross Primary Production (GPP) was exceeded by Ecosystem Respiration (ER). Downstream, where GPP was lower, the stream was usually strongly heterotrophic and prone to increasingly hypoxic conditions (i.e., insufficient oxygen) before streamflow ceased in summer. This coincided with lower velocities and deeper channels in beaver impacted areas. Seasonal and inter-annual variations in water quality were found to mainly correlate with hydroclimatic factors (particularly temperature) and their influence on streamflow. This study highlights that heterotrophy and hypoxia in lowland rivers in central Europe is an important seasonal feature of intermittent streams where agricultural landscapes continue leaching nutrients. These insights contribute to an evidence base for understanding how climate change will affect the quantity and quality of rural water resources in intermittent lowland streams with wetlands where the presence of beavers requires management responses.

High mountain catchment systems are inherently complex and include multiple processes that influence runoff generation, making it challenging to assess their current state and project their future solely based on observed data. However, combining observations with hydrological models that can simulate glacio-hydrological processes robustly offers a solution to this issue. This study focused on analysing and characterising the snow, glacier and runoff processes of the Tapado Glacier sub-catchment, an upstream source of the La Laguna reservoir in the semiarid Chilean Andes (30° S) for 2019–2021. For this purpose, a semi-distributed physical model (Cold Regions Hydrological Model [CRHM]) was used to simulate glacio-hydrological processes. The results indicate that sublimation accounted for 66%–89% of snow ablation, limiting the amount of snow available for melting in summer, and making melt from Tapado Glacier the primary component of mid-summer (January) discharge (28%–55%). This was reflected in significant mass loss from the Tapado Glacier ablation zone (−0.5 to −2.1 m w.e.). Sensitivity analyses indicated that precipitation and snow roughness generated the greatest variability in simulations related to snow mass balance process. Uncertainty due to errors in precipitation measurement and extrapolation is inherent in hydrological modelling in most mountain settings, whilst the uncertainty related to snow roughness (evaluated range: 0.0001–0.1 m) is largely due to its direct influence on snow sublimation rates and the challenges associated with measuring this variable. For the glaciated areas, results were sensitive to the selection of ice albedo. Whilst the Tapado sub-catchment includes only 1% of the catchment feeding the La Laguna reservoir (c.a. 27 km downstream), it equates to 6%–26% of monthly inflow into the reservoir over the study period. This indicates the importance of glaciated regions for supporting baseflow during relatively dry periods.