Hydrological Processes最新文献

Example of benchmark inputs and results for a snow-dominated basin, subset to a 4-year period on either side of the calculation (left) and evaluation (right) divide (dotted red line). KGE scores in legends are calculated for the evaluation period. (a) Observed streamflow, precipitation and a ‘rain plus melt’ flux (RPM) derived from precipitation and temperature. RPM is used to define the benchmarks shown in c and d. (b) Flow-only benchmarks. The straight light green line is the traditional (NSE = 0; KGE = 1-√2) mean flow benchmark. (c) Rainfall-runoff ratio benchmarks. A single rainfall-runoff ratio is derived from the data in the calculation period and used to scale annual and monthly RPM sums into flow benchmarks. (d) Simple models that represent catchment function.

This study explores the contribution of atmospheric rivers (ARs) to the water budget input of the Nechako River Basin (NRB) in British Columbia (BC), western Canada. The study quantifies the fraction of precipitation, rainfall, snowfall, and snow water equivalent (SWE) associated with ARs at multiple scales and tests for trends using the Mann–Kendall (MK) test. AR-related totals for 1950–2021 were created by linking AR events to water budget input variables of the ERA5-Land reanalysis product on a daily scale. Associations with different phases of the El Niño-Southern Oscillation (ENSO) climate pattern and AR-related contributions to the NRB are also investigated. Results indicate an increasing fractional contribution of rain in ARs landfalling in the NRB in the last two decades (2000–2019). Moreover, 21% of the total annual precipitation in the NRB is associated with ARs, with decreasing contributions from west to east. October has higher AR-related total precipitation than other months, while March, May and June are the least affected. ARs contribute disproportionately more to mid- and high-intensity daily precipitation totals, and provide up to 45% and 24% of the seasonal rainfall and snowfall, respectively. AR-related SWE is relatively higher in autumn due to the increased frequency and intensity of ARs, resulting in a greater fractional contribution of ARs to the snowpack compared to winter. ARs influence snowpack accumulation during fall (18%) and winter (13%) but also increase the risk of natural hazards. The MK test for AR-related water budget variables on the annual scale identified no significant trends. However, AR-related snowfall shows decreasing trends in the NRB, more specifically in the Upper Nechako, Lower Nechako and Stellako sub-basins during the summer. Over the study period, ARs consistently contribute up to one-fifth of the annual input to the NRB's water budget. This study provides the first quantitative assessment and trend analyses of AR contributions to the water budget input of a reservoir-regulated watershed in north-central BC, yielding valuable information for hydropower production, ecological flows, irrigation, domestic and industrial water use.

Forested headwater catchments ensure good water quality for downstream ecosystems and human consumption. Climate change and the exacerbating likelihood of extreme events elevate the risk of severe forest dieback. However, the effects of forest dieback on the quantity and quality of stream water are not fully understood. Here, we analyse high-frequency observations of discharge, electrical conductivity (EC), dissolved organic carbon (DOC) and nitrate (NO₃N) obtained before, during and after a drought-induced forest dieback in a headwater stream in the German Harz Mountains. We focus on the characteristics of concentration-discharge (C-Q) relationships at the scale of runoff events to assess the effects of forest dieback on the sources, mobilisation and pathways of EC, DOC and NO₃N. When comparing pre- and post-dieback conditions, we found a significant increase in runoff efficiency and a doubling of DOC loads exported from the catchment, while DOC concentrations increased only moderately and their C-Q patterns did not change. EC exhibit no changes in concentrations but a steepening of C-Q dilution patterns. We explain these findings with a dieback-induced decrease in evapotranspiration, which leads to more intensive drainage of the upper organic soil layers in the riparian zone. In contrast, we observed a strong increase in NO₃N concentrations and fluxes by a factor of ~5, while C-Q patterns at the event scale changed from enrichment to dilution. We argue that the dieback led to an excess of NO₃N on the hillslopes that connect to the stream via surficial flowpaths. In this way, NO₃N bypasses the riparian zone, reducing the catchment's efficiency in attenuating this nutrient. Our study emphasises the pivotal role of riparian zones in mediating water quality in headwater streams. Different configurations of the riparian zone and its connection to the hillslopes and the stream network may be a missing piece in explaining differences in water quality responses of catchments to forest dieback.

Zero-flow recordings in gauged streamflow data are critically important for intermittent stream research. Acknowledging the high uncertainty in zero-flow recordings, many studies pick a small number as zero-flow threshold, below which the flow is considered to be zero. The choice of zero-flow threshold is often arbitrary or unjustified, which leads us to wonder: would selecting a slightly different threshold change analysis result significantly? Here, we used a simple sensitivity analysis to assess how the choice of zero-flow threshold impacts the calculated values of relevant metrics to intermittent stream research. Results show that these metrics tended to be more sensitive to lower zero-flow thresholds, suggesting that even choosing a slightly different threshold could lead to meaningfully different results from the management perspective. This study highlights the need for reasonable justification of the choice of zero-flow threshold and concludes with potential ways to reduce uncertainty in zero-flow measurement.

The establishment of SPAC (soil–plant-atmosphere continuum) stations is essential for comprehensive monitoring of land-atmosphere interactions and ecological and hydrological processes. This paper addresses the critical limitations of existing observation networks, which often rely on single-aspect observations, resulting in insufficient data for a holistic understanding of SPAC dynamics. Specifically, SPAC stations provide critical multi-variable observations that enhance process-based model calibration and physical constraints and improve the empirical basis of data-driven models. Advanced technologies such as machine learning and remote sensing are proposed to transform current weather and soil moisture stations into quasi-SPAC sites capable of estimating carbon and water flux data. Additionally, the strategic placement of new SPAC sites in regions projected to be sensitive to future climate change and climate risks, as indicated by models such as CMIP6, is recommended. Furthermore, promoting comprehensive observational systems like Europe's Integrated Carbon Observation System (ICOS) in other regions, establishing a unified management framework and coordinating the upgrading of existing global observation networks are essential steps. Ultimately, the proposed enhancements will advance global ecological and hydrological studies, providing a more integrated and accurate understanding of the SPAC system and its responses to climate variability.

Stream sediment transport results from a convolution of climate, weather, geology, topography, biology, and human influence. In addition to providing water and food security for rural dryland communities, sand dams—small weirs designed to trap only the coarse fractions of transported sediments in seasonal and ephemeral streams—highlight many complexities of geomorphological dynamics. Sand dams store water in interstitial riverbed pores and the size of deposited sediment particles largely determines the recoverability of stored water: Fine materials limit transmission and provide lower volumetric yield. In this study, we seek to identify a practical method for evaluating the theoretical effect of staged sand dam crest construction on key sediment-trapping processes for a proposed dam site. We argue that the Rouse number provides a useful criterion for identifying regimes where the target material grades are trapped. These ideas were tested using sediment data collected in Kenya and US Army Corps of Engineers River Analysis System numerical simulations to evaluate the sensitivity of sedimentation processes to crest height. We show that constructing sand dams in stages results in more targeted trapping of coarse material. Sedimentation is shown to be more sensitive to variation in crest height than the flood hydrograph, especially when a dam's crest height is small. By introducing a method to assess the necessity and inform design of staged crest construction based on local flow dynamics, this study offers a framework for optimising sand dam performance in data-scarce environments. This approach provides a means to balance construction costs with expected benefits, enhancing the sustainability and functionality of sand dams in arid and semi-arid regions.