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Water temperature has an important impact on many aspects of basin hydrology and ecology. In the northern regions, investigation of river thermal regimes and their changes over space and time is a challenge because of data limitations. This study determines the water temperature regimes at several locations within the Yukon and Mackenzie River basins and examines their relationship with air temperature. The Yukon and Mackenzie Rivers have distinct water temperature dynamics. They remain near zero from freeze-up in the fall to ice breakup in the spring and reach their peak temperature during mid-summer. For the locations examined, peak mean monthly water temperatures ranged from 9° to 15°C, and mean July air temperatures ranged from 13° to 16°C. The lags between water and air temperatures ranged from 1 to 40 days. The largest lag was found at the Great Bear River monitoring location, since water temperature at this site is strongly influenced by the heat storage of Great Bear Lake. Tests of three models, linear regression, logical regression (s-shape), and the physically based air2stream model, show that the air2stream model provided the best results, followed by logical regression. Linear regression gave the poorest result. Model estimates of water temperature from air temperature were slightly improved by the inclusion of discharge data. The water temperature sampling regimes had a considerable effect on model performance; long-term data provide a more robust test of a model. Comparisons of mean monthly water temperatures suggest significant spatial variability and some inconsistency between upstream and downstream sites that is due mainly to differences in data collection schemes. This study strongly demonstrates the need to improve water temperature monitoring in the northern regions. La température de l'eau a de grandes incidences sur de nombreux aspects de l'hydrologie et de l'écologie des bassins. Dans les régions nordiques, l'étude des régimes thermiques des cours d'eau et de leurs changements au fil du temps et de l'espace pose des difficultés en raison des limites qu'imposent les données. La présente étude détermine les régimes des températures de l'eau en maints endroits des bassins de la rivière Yukon et du fleuve Mackenzie et examine leur relation avec la température de l'air. La rivière Yukon et le fleuve Mackenzie ont des dynamiques distinctes en matière de température de l'eau. De la prise de la glace de l'automne jusqu'à la débâcle du printemps, les températures de ces cours d'eau se situent à près de zéro, et c'est vers le milieu de l'été que leurs températures augmentent le plus. Dans le cas des sites à l'étude, les températures mensuelles moyennes les plus élevées de l'eau ont atteint entre 9° et 15 °C, tandis que les températures moyennes de l'air en juillet ont varié entre 13° et 16 °C. Le décalage entre les températures de l'eau et de l'air a fluctué entre un et 40 jours. Le plus grand décalage a été enregistré au site de surveillance de la rivière Great Bear, la température de l'eau à cet emplacement étant fortement influencée par le stockage de la chaleur dans le lac Great Bear. Des essais effectués à l'aide de trois modèles, soit la régression linéaire, la régression logique (en forme de s) et le modèle air2stream aux caractéristiques physiques indiquent que le modèle air2stream a donné les meilleurs résultats, suivi de la régression logique. Les résultats les moins bons ont été obtenus au moyen de la régression linéaire. Les estimations du modèle de la température de l'eau à partir de la température de l'air ont été légèrement améliorées avec l'inclusion des données du débit. Les régimes d'échantillonnage de la température de l'eau ont eu un effet considérable sur le rendement du modèle; les données à long terme ont permis d'obtenir un essai de modèle plus robuste. La comparaison des températures moyennes mensuelles de l'eau suggère une variabilité spatiale importante et certaines incohérences entre les sites en amont et les sites en aval, principalement en raison des différences dans les modes de collecte des données. Cette étude montre à quel point il est important d'améliorer la surveillance des températures de l'eau dans les régions nordiques.

Combining π‐conjugated and non‐π‐conjugated groups is an important strategy for synthesizing new nonlinear optical (NLO) crystals. However, the second harmonic generation (SHG) response and optical anisotropy can be limited by improper spatial alignment of these functional groups in the crystal structure. In this work, it is revealed that non‐π‐conjugated [NH2SO3] group acts as both hydrogen bond donor and acceptor, effectively regulating the 2D planar structure formed by π‐conjugated [C4N3H6] groups. The resulting organic–inorganic hybrid crystal C4N3H6SO3NH2 exhibits a strong SHG response (2.5 × KDP), large optical anisotropy (0.233@546 nm), and blue‐violet and green fluorescence near 360 and 520 nm, respectively. This work expands the methodology for creating new NLO crystals through organic–inorganic hybridization, while also showcasing the potential of C4N3H6SO3NH2 as a multifunctional optical material. A multifunctional material C4N3H6SO3NH2 is synthesized with excellent linear and nonlinear optical properties as well as ultraviolet (UV) light‐switchable fluorescence.

For a graph$G$and an integer$k\\geq 2$ , a$\\chi'_{k}$ -coloring of$G$is an edge coloring of$G$such that the subgraph induced by the edges of each color has all degrees congruent to$1 ~ (\\mod k)$ , and$\\chi'_{k}(G)$is the minimum number of colors in a$\\chi'_{k}$ -coloring of$G$ . In [\"The mod$k$chromatic index of graphs is$O(k)$ \", J. Graph Theory. 2023; 102: 197-200], Botler, Colucci and Kohayakawa proved that$\\chi'_{k}(G)\\leq 198k-101$for every graph$G$ . In this paper, we show that$\\chi'_{k}(G) \\leq 177k-93$ .

Under global warming, many glaciers worldwide are receding. However, recent studies have suggested the extension of the Karakoram Anomaly, a region of anomalous glacier mass gain, into the western Kunlun and eastern Pamir mountains. However, the eastern limit of this anomaly in the Kunlun Mountains is unclear. This study, using changes in glacier area and surface elevation, estimates the eastern limit of the Kunlun-Pamir-Karakoram anomaly at ~85°E. Over the past 50 years, glaciers west of 85°E in the Kunlun Mountains decreased in area from 8401 to 7945 km2 at a rate of −0.12 ± 0.07% a−1, showed a reduction in the rate of retreat through time and have recently gained mass, with surface elevation changes of 0.15 ± 0.35 m a−1 over the period of 2000–2013. Glaciers east of 85°E have experienced greater rates of area change (−61 ± 12 km2 and −0.43 ± 0.13% a−1) over the past 50 years, accelerated area loss in recent years and elevation change rate of −0.51 ± 0.18 m a−1 between 2000 and 2013. These patterns of elevation and area change are consistent with regional increases in summer temperature in the eastern Kunlun Mountains and slight cooling in the western Kunlun Mountains.

Sea surface salinity (SSS) links various components of the Arctic freshwater system. SSS responds to freshwater inputs from river discharge, sea ice change, precipitation and evaporation, and oceanic transport through the open straits of the Pacific and Atlantic oceans. However, in situ SSS data in the Arctic Ocean are very sparse and insufficient to depict the large-scale variability to address the critical question of how climate variability and change affect the Arctic Ocean freshwater. The L-band microwave radiometer on board the NASA Soil Moisture Active Passive (SMAP) mission has been providing SSS measurements since April 2015, at approximately 60 km resolution with Arctic Ocean coverage in 1–2 days. With improved land/ice correction, the SMAP SSS algorithm that was developed at the Jet Propulsion Laboratory (JPL) is able to retrieve SSS in ice-free regions 35 km of the coast. SMAP observes a large-scale contrast in salinity between the Atlantic and Pacific sides of the Arctic Ocean, while retrievals within the Arctic Circle vary over time, depending on the sea ice coverage and river runoff. We assess the accuracy of SMAP SSS through comparative analysis with in situ salinity data collected by Argo floats, ships, gliders, and in field campaigns. Results derived from nearly 20,000 pairs of SMAP and in situ data North of 50°N collocated within a 12.5-km radius and daily time window indicate a Root Mean Square Difference (RMSD) less than ~1 psu with a correlation coefficient of 0.82 and a near unity regression slope over the entire range of salinity. In contrast, the Hybrid Coordinate Ocean Model (HYCOM) has a smaller RMSD with Argo. However, there are clear systematic biases in the HYCOM for salinity in the range of 25–30 psu, leading to a regression slope of about 0.5. In the region North of 65°N, the number of collocated samples drops more than 70%, resulting in an RMSD of about 1.2 psu. SMAP SSS in the Kara Sea shows a consistent response to discharge anomalies from the Ob’ and Yenisei rivers between 2015 and 2016, providing an assessment of runoff impact in a region where no in situ salinity data are available for validation. The Kara Sea SSS anomaly observed by SMAP is missing in the HYCOM SSS, which assimilates climatological runoffs without interannual changes. We explored the feasibility of using SMAP SSS to monitor the sea surface salinity variability at the major Arctic Ocean gateways. Results show that although the SMAP SSS is limited to about 1 psu accuracy, many large salinity changes are observable. This may lead to the potential application of satellite SSS in the Arctic monitoring system as a proxy of the upper ocean layer freshwater exchanges with subarctic oceans.

Lake water level reflects the dynamic balance of water input and output/loss and is a sensitive indicator of climate change and variation. Studying the relationship between the closed Qinghai Lake water level and watershed climate change is important for understanding regional climate change and its impacts on the lake. The objective of this study was to investigate changes in Qinghai Lake water level/area and environmental factors during 1961–2019, using ground-based measurements data, hydrological balance model and statistical methods. The results revealed two primary phases: during the first phrase (1961–2004), the lake water level lowered by 0.80 m/ decade (p < 0.01), while in the second phase (2004–2019), it rose markedly by 1.80 m/decade (p < 0.01). The lake area increased in April and September between 1990 and 2019, but since 2004 the increases have been more significant. Air temperature near the lake during 1961–2019 warmed by 0.39°C/decade and precipitation increased by 17 mm/decade. Annual river runoff increased at 14.3 mm/decade from 1961 to 2019, however, runoff decreased (−6.8 mm/decade) during the first phase from 1961 to 2004 and increased significantly (84.7 mm/decade) during the second phase from 2004 to 2019. The increases in precipitation and river runoff were the predominant factors contributing to lake water level rises and area expansion, while a decreasing lake water level and area reduction corresponded to reduced precipitation and river runoff and increased evaporation. As a sensitive indicator of regional climate change, the fluctuations of lake water level and surface area provide a comprehensive reflection of climate change in the Qinghai Lake watershed.

We use monthly discharge and permafrost data to examine the relationship between discharge characteristics and basin permafrost coverage for the nested subbasins of the Lena River in Siberia. There are similarity and variation in streamflow regimes over the basin. The ratios of monthly maximum/minimum flows directly reflect discharge regimes. The ratios increase with drainage area from the headwaters to downstream within the Lena basin. This pattern is different from the nonpermafrost watersheds, and it clearly reflects permafrost effect on regional hydrological regime. There is a significant positive relationship between the ratio and basin permafrost coverage. This relationship indicates that permafrost condition does not significantly affect streamflow regime over the low permafrost (less than 40%) regions, and it strongly affects discharge regime for regions with high permafrost (greater than 60%). Temperature and precipitation have similar patterns among the subbasins. Basin precipitation has little association with permafrost conditions and an indirect relation with river flow regimes. There exists a good relation between the freezing index and permafrost extent over the basin, indicating that cold climate leads to high coverage of permafrost. This relation relates basin thermal condition with permafrost distribution. The combination of the relations between temperature versus permafrost extent, and permafrost extent versus flow ratio links temperature, permafrost, and flow regime over the Lena basin. Over the Aldan subbasin, the maximum/minimum discharge ratios significantly decrease during 1942–1998 due to increase in base flow; this change is consistent in general with permafrost degradation over eastern Siberia.

The western cordillera supplies freshwater across much of western Canada mainly through meltwater from snow and ice. This “alpine water tower” has been, and is projected to be, associated with changes in the seasonality and amount of freshwater availability, which are critical in supporting the societal and environmental flow needs of the region. This study incorporates existing information to synthesize and evaluate current and future freshwater supplies and demands across major north-, west-, and east-flowing sub-basins of the Canadian western cordillera. The assessment of supply indicators reveals several historical changes that are projected to continue, and be exacerbated, particularly by the end of this century and under a high emission scenario. The greatest and most widespread impact is the seasonality of streamflow characterized by earlier spring freshets, increased winter, and decreased summer flow. Future winter and spring warming over all basins will result in decreases in end of season snow and glacier mass balance with greatest declines in more southern regions. In many areas, there will be a greater likelihood of summer freshwater shortages. All sub-basins have environmental and economic freshwater demands and pressures, especially in more southern watersheds where population and infrastructure are more prevalent and industrial, agricultural, and water energy needs are higher. Concerns regarding the continued ability to maintain suitable aquatic habitats and adequate water quality are issues across all regions. These water supply changes along with continued and increasing demands will combine to create a variety of freshwater vulnerabilities across all regions of western Canada. Southern basins including the South Saskatchewan and Okanagan are likely to experience the greatest vulnerabilities due to future summer freshwater supply shortages and increasing economic demands. In more northern areas, vulnerabilities primarily relate to how the rapidly changing landscape (mainly associated with permafrost thaw) impacts freshwater quantity and quality. These vulnerabilities will require various adaptation measures in response to alterations in the timing and amount of future freshwater supplies and demands.

Although precipitation has been measured for many centuries, precipitation measurements are still beset with significant inaccuracies. Solid precipitation is particularly difficult to measure accurately, and wintertime precipitation measurement biases between different observing networks or different regions can exceed 100 %. Using precipitation gauge results from the World Meteorological Organization Solid Precipitation Intercomparison Experiment (WMO-SPICE), errors in precipitation measurement caused by gauge uncertainty, spatial variability in precipitation, hydrometeor type, crystal habit, and wind were quantified. The methods used to calculate gauge catch efficiency and correct known biases are described. Adjustments, in the form of transfer functions that describe catch efficiency as a function of air temperature and wind speed, were derived using measurements from eight separate WMO-SPICE sites for both unshielded and single-Alter-shielded precipitation-weighing gauges. For the unshielded gauges, the average undercatch for all eight sites was 0.50 mm h−1 (34 %), and for the single-Alter-shielded gauges it was 0.35 mm h−1 (24 %). After adjustment, the mean bias for both the unshielded and single-Alter measurements was within 0.03 mm h−1 (2 %) of zero. The use of multiple sites to derive such adjustments makes these results unique and more broadly applicable to other sites with various climatic conditions. In addition, errors associated with the use of a single transfer function to correct gauge undercatch at multiple sites were estimated.