长江中游地区暴雨过程的500 hPa信号场特征

文中用500 hPa信号场研究了长江中游地区暴雨发生的气候异常环境,并提出用信号场合成图的检验方法来分析暴雨规律.结果表明,暴雨过程与无雨过程在500 hPa信号场中异常信号显著区的出现及分布形势有明显不同.分析14次暴雨过程的合成图,发现在发生暴雨过程第1天,正异常区常常出现在贝加尔湖附近地区(40°～50°N,80°～100°E)和中国华南地区(20°～25°N,100°～130°E),负异常区出现在中国长江中游北部地区.暴雨过程出现的主要特征是在110°E附近,形成南北向的"+-+"分布形势和波列.     

Assessing impacts of cemeteries on water quality in an urban headwater watershed with mixed human-built infrastructure

Cemeteries are understudied integral components to urban watersheds, which provide ecosystem services but can also export nutrients, trace elements, and other contaminants to nearby water bodies. In this study, we focus on Meadowbrook Creek, an urban headwater stream in Syracuse, New York (USA), which has shown significant nitrate contributions from a local cemetery. We collected biweekly surface water samples over the course of 1 year from 2022 to 2023 for analysis of major and trace elemental concentrations including Na, Ca, Mg, K, F, Cl, sulfate, and nitrate. Here, we aim to assess the impact of various human infrastructures on urban stream water quality with a particular focus on the cemetery and nitrate. A comparison between the new dataset in this study and previously reported water chemistry data in Meadowbrook in 2012 suggests a decade-long impact of road salting and the cemetery on water quality particularly with respect to Na, Cl, and nitrate. Sulfate, Mg, Ca, and K are likely mainly geogenic. Stable nitrogen isotope data, the usage of concrete or steel vaults in the cemetery in the past 50 years, and the lack of correlation between nitrate and fluoride concentrations in stream water argue against burial decay products being a major source of nitrate to the stream. Instead, other nitrate sources that exist in the cemetery such as, fertilizer, decaying plant material, and wastewater, are more viable dominant nitrate sources. In addition, nitrate loading calculations indicate that the groundwater-connected reach, including the cemetery, acts as an annual net sink for nitrate despite the seasonally varying sink-source patterns.     

Multidecadal trend analysis of hydrological drought along River Niger using the Streamflow Drought Index

Droughts affect human well-being and the economy of countries across the world. Understanding the long-term evolution of droughts within a particular region will help in drought mitigation and adaptation plans, thereby reducing drought impact on the environment. This study examined the multidecadal trends in hydrological droughts at two stations along River Niger using 3-month, 6-month, and annual time scales. Hydrological drought events were identified using the streamflow drought index (SDI) between 1915 and 1990 based on the Theil-Sen slope and Mann-Kendall approaches. Across the timescales, extreme and severe droughts occurred in 1982/84 and 1983/84 with -2 ≤ S_d < -1.5. On an annual scale, the results from the annual SDI further showed that the 7th and 8th decades (1971−1990) recorded more drought events of varying degrees ranging from mild to extreme drought in both stations than in other decades. The last two decades (7th and 8th) further revealed the most extended hydrological drought duration from 1974/75 to 1988/89 for Baro and from 1979/80 to 1988/89 for Lokoja. The highest severity recorded at Baro was -15.56 and -14.26 at Lokoja. The prolonged duration of drought events across the stations and their associated yearly intensities suggests that more proactive measures are needed to ameliorate the hydrological drought impact in the study area.