Increasing volatility of reconstructed Morava River warm-season flow, Czech Republic.

Study region: The Morava River basin, Czech Republic, Danube Basin, Central Europe. Study focus: Hydrological summer extremes represent a prominent natural hazard in Central Europe. River low flows constrain transport and water supply for agriculture, industry and society, and flood events are known to cause material damage and human loss. However, understanding changes in the frequency and magnitude of hydrological extremes is associated with great uncertainty due to the limited number of gauge observations. Here, we compile a tree-ring network to reconstruct the July-September baseflow variability of the Morava River from 1745 to 2018 CE. An ensemble of reconstructions was produced to assess the impact of calibration period length and trend on the long-term mean of reconstruction estimates. The final estimates represent the first baseflow reconstruction based on tree rings from the European continent. Simulated flows and historical documentation provide quantitative and qualitative validation of estimates prior to the 20th century. New hydrological insights for the region: The reconstructions indicate an increased variability of warm-season flow during the past 100 years, with the most extreme high and low flows occurring after the start of instrumental observations. When analyzing the entire reconstruction, the negative trend in baseflow displayed by gauges across the basin after 1960 is not unprecedented. We conjecture that even lower flows could likely occur in the future considering that pre-instrumental trends were not primarily driven by rising temperature (and the evaporative demand) in contrast to the recent trends.

Decoupled spatiotemporal patterns of avian taxonomic and functional diversity.

Each year, seasonal bird migration leads to an immense redistribution of species occurrence and abundances,1,2,3 with pervasive, though unclear, consequences for patterns of multi-faceted avian diversity. Here, we uncover stark disparities in spatiotemporal variation between avian taxonomic diversity (TD) and functional diversity (FD) across the continental US. We show that the seasonality of species richness expectedly3 follows a latitudinal gradient, whereas seasonality of FD instead manifests a distinct east-west gradient. In the eastern US, the temporal patterns of TD and FD are diametrically opposed. In winter, functional richness is highest despite seasonal species loss, and the remaining most abundant species are amassed in fewer regions of the functional space relative to the rest of the year, likely reflecting decreased resource availability. In contrast, temporal signatures for TD and FD are more congruent in the western US. There, both species and functional richness peak during the breeding season, and species' abundances are more regularly distributed and widely spread across the functional space than during winter. Our results suggest that migratory birds in the western US disproportionately contribute to avian FD by possessing more unique trait characteristics than resident birds,4,5 while the primary contribution of migrants in the eastern US is through increasing the regularity of abundances within the functional space relative to the rest of the year. We anticipate that the uncovered complexity of spatiotemporal associations among measures of avian diversity will be the catalyst for adopting an explicitly temporal framework for multi-faceted biodiversity analysis.

Orographic amplification of El Niño teleconnections on winter precipitation across the Intermountain West of North America.

A large proportion of western North America experiences regular water stress, compounded by high seasonal and interannual variability. In the Intermountain West region, the El Niño/Southern Oscillation (ENSO) is a critical control on winter precipitation, but the nature of this signal is entangled with a combination of orographic effects and long-term climate trends. This study employs a spatially distributed, nonlinear spline model to isolate ENSO impacts from these other factors using gauge-based observations starting in 1871. In contrast to previous modelling approaches, our approach uses original gauge data, without shortening the record to accommodate a common period. This enables more detailed separation of ENSO effects from the confounding influence of topography and long-term trends, whereas the longer time frame permits more robust correlation with the ENSO signal. Here we show that the complex topography of the Intermountain West exaggerates the underlying ENSO signal, producing a 2.3-5.8 times increase in the range of ENSO-induced precipitation changes along high-elevation western slopes relative to lower elevations. ENSO effects on winter precipitation can be as large as ± 100 mm at high elevations. Further, our approach reveals that the previously recognized dipolar pattern of positive (negative) association of ENSO with precipitation in the south (north) manifests as an incremental relationship in the south but as a near-binary switch in effects between El Niño and La Niña in the north. The location and extent of the strongest precipitation differences vary during the positive and negative ENSO phases within each region. The intricacies of these spatial- and elevation-based modulations of ENSO impacts are especially informative for the northern centre of this dipole, where ENSO-precipitation relationships have previously been difficult to resolve.

Author Correction: Assessing data availability and research reproducibility in hydrology and water resources.

In the original version of this Article the author of reference #38 was incorrectly stated as Quinn, J. et al. This has been corrected to Xu, W. et al. in both the HTML and PDF versions.

Assessing data availability and research reproducibility in hydrology and water resources.

There is broad interest to improve the reproducibility of published research. We developed a survey tool to assess the availability of digital research artifacts published alongside peer-reviewed journal articles (e.g. data, models, code, directions for use) and reproducibility of article results. We used the tool to assess 360 of the 1,989 articles published by six hydrology and water resources journals in 2017. Like studies from other fields, we reproduced results for only a small fraction of articles (1.6% of tested articles) using their available artifacts. We estimated, with 95% confidence, that results might be reproduced for only 0.6% to 6.8% of all 1,989 articles. Unlike prior studies, the survey tool identified key bottlenecks to making work more reproducible. Bottlenecks include: only some digital artifacts available (44% of articles), no directions (89%), or all artifacts available but results not reproducible (5%). The tool (or extensions) can help authors, journals, funders, and institutions to self-assess manuscripts, provide feedback to improve reproducibility, and recognize and reward reproducible articles as examples for others.

Observed drought indices show increasing divergence across Europe.

Recent severe European droughts raise the vital question: are we already experiencing measurable changes in drought likelihood that agree with climate change projections? The plethora of drought definitions compounds this question, requiring instead that we ask: how have various types of drought changed, how do these changes compare with climate projections, and what are the causes of observed differences? To our knowledge, this study is the first to reveal a regional divergence in drought likelihood as measured by the two most prominent meteorological drought indices: the Standardized Precipitation Index (SPI) and the Standardized Precipitation-Evapotranspiration Index (SPEI) across Europe over the period 1958-2014. This divergence is driven primarily by an increase in temperature from 1970-2014, which in turn increased reference evapotranspiration (ET0) and thereby drought area measured by the SPEI. For both indices, Europe-wide analysis shows increasing drought frequencies in southern Europe and decreasing frequencies in northern Europe. Notably, increases in temperature and ET0 have enhanced droughts in southern Europe while counteracting increased precipitation in northern Europe. This is consistent with projections under climate change, indicating that climate change impacts on European drought may already be observable and highlighting the potential for discrepancies among standardized drought indices in a non-stationary climate.

Performance of grass swales for improving water quality from highway runoff.

The performance of grass swales for treating highway runoff was evaluated using an experimental design that allowed for influent and effluent flow and pollutant concentration measurements to be taken at specific intervals through each storm event. Two common swale design alternatives, pre-treatment grass filter strips and vegetated check dams, were compared during 45 storm events over 4.5 years. All swale alternatives significantly removed total suspended solids and all metals evaluated: lead, copper, zinc, and cadmium. The probability of instantaneous concentrations exceeding 30 mg/L TSS was decreased from 41-56% in the untreated runoff to 1-19% via swale treatment. Nutrient treatment was variable, with generally positive removal except for seasonal events with large pulses of release from the swales. Nitrite was the only consistently removed nutrient constituent. Chloride concentrations were higher in swale discharges in nearly every measurement, suggesting accumulation during the winter and release throughout the year. Sedimentation and filtration within the grass layer are the primary mechanisms of pollutant treatment; correspondingly, particles and particulate-bound pollutants show the greatest removal via swales. Inclusion of filter strips or check dams had minimal effects on water quality.

Hydraulic performance of grass swales for managing highway runoff.

The hydraulic performance of grass swales as a highway stormwater control measure was evaluated in a field-scale study adjacent to a Maryland highway. Two common swale design alternatives, pretreatment grass filter strips and vegetated check dams, were compared during 52 storm events over 4.5 years. Swale performance is described via three regimes, dependent on the relative size of the rainfall event. Overall, half of the events were small enough that the entire flow was stored, infiltrated, and evapotranspirated by the swales, resulting in no net swale discharge. Swales significantly reduced total volume and flow magnitudes generally during events with rainfall less than 3 cm. While the majority of improvement can be attributed to the swales, inclusion of check dams increases swale effectiveness. Pretreatment grass filter strips produced mixed effects. The swales demonstrated essentially no volumetric reduction during large storm events, functioning instead as conveyance, and smoothing fluctuations in flow.