Impacts of upper tropospheric cooling upon the late spring drought in East Asia simulated by a regional climate model

Responses of late spring （21 April 20 May） rainfall to the upper tropospheric cooling over East Asia are investigated with a regional climate model based on Laboratoire de M6t6orologie Dynamique Zoom （LMDZ4-RCM）. A control experiment is performed with two runs driven by the mean ERA-40 data during 1958-1977 and 1981 2000, respectively. The model reproduces the major decadal-scale circulation changes in late spring over East Asia, including a cooling in the upper troposphere and an anomalous meridional cell. Accordingly, the precipitation decrease is also captured in the southeast of the upper-level cooling region. To quantify the role of the upper-level cooling in the drought mechanism, a sensitivity experiment is further conducted with the cooling imposed in the upper troposphere. It is demonstrated that the upper-level cooling can generate the anomalous meridional cell and consequently the drought to the southeast of the cooling center. Therefore, upper tropospheric cooling should have played a dominant role in the observed late spring drought over Southeast China in recent decades.     

Groundwater flow and storage processes in an inactive rock glacier

Groundwater flow through coarse blocky landforms contributes to streamflow in mountain watersheds, yet its role in the alpine hydrologic cycle has received relatively little attention. This study examines the internal structure and hydrogeological characteristics of an inactive rock glacier in the Canadian Rockies using geophysical imaging techniques, analysis of the discharge hydrograph of the spring draining the rock glacier, and chemical and stable isotopic compositions of source waters. The results show that the coarse blocky sediments forming the rock glacier allow the rapid infiltration of snowmelt and rain water to an unconfined aquifer above the bedrock surface. The water flowing through the aquifer is eventually routed via an internal channel parallel to the front of the rock glacier to a spring, which provides baseflow to a headwater stream designated as a critical habitat for an at‐risk cold‐water fish species. Discharge from the rock glacier spring contributes up to 50% of basin streamflow during summer baseflow periods and up to 100% of basin streamflow over winter, despite draining less than 20% of the watershed area. The rock glacier contains patches of ground ice even though it may have been inactive for thousands of years, suggesting the resiliency of the ground thermal regime under a warming climate.     

Soil frost effects on streamflow recessions in a subarctic catchment

The Arctic is warming rapidly. Changing seasonal freezing and thawing cycles of the soil are expected to affect river run‐off substantially, but how soil frost influences river run‐off at catchment scales is still largely unknown. We hypothesize that soil frost alters flow paths and therefore affects storage–discharge relations in subarctic catchments. To test this hypothesis, we used an approach that combines meteorological records and recession analysis. We studied streamflow data (1986–2015) of Abiskojokka, a river that drains a mountainous catchment (560 km²) in the north of Sweden (68° latitude). Recessions were separated into frost periods (spring) and no‐frost periods (summer) and then compared. We observed a significant difference between recessions of the two periods: During spring, discharge was linearly related to storage, whereas storage–discharge relationships in summer were less linear. An analysis of explanatory factors showed that after winters with cold soil temperatures and low snowpack, storage–discharge relations approached linearity. On the other hand, relatively warm winter soil conditions resulted in storage–discharge relationships that were less linear. Even in summer, relatively cold antecedent winter soils and low snowpack levels had a propagating effect on streamflow. This could be an indication that soil frost controls recharge of deep groundwater flow paths, which affects storage–discharge relationships in summer. We interpret these findings as evidence for soil frost to have an important control over river run‐off dynamics. To our knowledge, this is the first study showing significant catchment‐integrated effects of soil frost on this spatiotemporal scale.     

Long‐term effects of aquifer overdraft and recovery on groundwater quality in a Ramsar wetland: Las Tablas de Daimiel National Park,Spain

Las Tablas de Daimiel National Park is one of Spain's most representative groundwater‐dependent ecosystems. Under natural conditions, water inflows combined brackish surface water from River Gigüela with freshwater inputs from River Guadiana and the underlying aquifer. Since the mid‐1970s, aquifer overexploitation caused the desiccation of the wetlands and neighbouring springs. The National Park remained in precarious hydrological conditions for three decades, with the only exception of rapid floods due to extreme rainfall events and sporadic water transfers from other basins. In the late 2000s, a decrease in groundwater abstraction and an extraordinarily wet period reversed the trend. The aquifer experienced an unexpected recovery of groundwater levels (over 20 m in some areas), thus restoring groundwater discharge to springs and wetlands. The complex historical evolution of the water balance in this site has resulted in substantial changes in surface and groundwater quality. This becomes evident when comparing the pre‐1980 groundwater quality and the hydrochemical status in the wetland in two different periods, under “dry” and “wet” conditions. Although the system is close to full recovery from the groundwater‐level viewpoint, bouncing back in the major hydrochemical constituents has not yet been obtained. These still appear to evolve in response to the previous overexploitation state. Moreover, in some sectors, there are groundwater‐dependent ecosystems that remain different to those found in preoverexploitation times. The experience of Las Tablas de Damiel provides an observatory of long‐term changes in wetland water quality, demonstrating that the effects of aquifer overexploitation on aquatic ecosystems are more than a mere alteration of the water balance and that groundwater quality is the key to aquifer and aquatic ecosystem sustainability.     

四川石棉公益海温泉水文地球化学特征

利用水文地球化学数据建立温泉水文循环模型, 探讨温泉水文地球化学变化与地震的关系, 对中强地震短临流体异常判断具有重要的意义。 通过对石棉公益海温泉水常量元素、 微量元素和氢氧同位素以及锶同位素的测量, 探讨了该区域水文地球化学时空变化特征。 因此, 于2008年10月至2019年9月, 共对公益海温泉采集水样206个, 并对温泉水中离子组分和浓度, 温泉逸出气组分、 温泉气体同位素、 碳同位素和氢氧同位素含量进行测量。 分析结果表明: ① 公益海温泉主要为Na-HCO₃·Cl型水, δD、 δ¹⁸O同位素测值分别为-14.19‰~-14.83‰和-108.67‰~-110.47‰, 分布于大气降水线附近, 说明温泉水主要源于大气降水; ② 据SiO₂地温计计算热储温度约94.12℃, 循环深度约4.3 km, 表明大气降水入渗地下, 在热源加热后, 沿着断层和裂隙循环到地表, 形成温泉补给; 并且, 锶同位素和微量元素研究发现, ⁸⁷Sr和⁸⁶Sr主要来自硅酸盐类矿物, 微量元素含量较低, 水岩反应程度较弱; ③ 通过对研究区进行长时间连续观测发现, 在公益海周围300 km范围内的3个五级以上的地震使温泉水中常量元素的浓度, 分别出现了震前异常、 同震响应和震后效应。 推测这可能是因为公益海温泉位于公益海断裂和安宁河断裂的交会区, 推测周围的地震会触发公益海温泉水中的离子地球化学特征产生变化。 结合已有地质资料与公益海温泉水文地球化学数据, 建立公益海断裂带温泉水文循环模型, 这些对公益海断裂带周围未来中强地震短临流体异常判断具有重要的意义。     

小流量、低水头观测泉脱?集气装置改造实验研究——以延庆松山泉气氡为例

小流量、低水头观测泉使用常规脱?集气装置,达不到观测气量的要求,会直接影响化学气体观测质量。本文以松山观测泉为研究对象,结合台站观测条件,通过技术改造和实验研究,制作了恒流溅落式脱?集气装置,对气氡观测结果进行了连续观测分析,获得了完整的年动态变化曲线。观测结果表明,该脱?集装置能够较好地解决小流量、低水头观测泉存在的流量、气量、水量不稳定的问题,使气氡观测的稳定性得到明显提高,为全国其他小流量、低水头观测泉脱?集气装置的技术改进提供了范例。     

Spring mesoscale high in the western South China Sea

A recurring spring mesoscale eddy in the western South China Sea (SCS) is studied using remote sensing data and historical in situ observations. The feature first appears east of the central Vietnam coast in February as a high sea-level anomaly, grows rapidly to a well-developed anticyclonic eddy by March, matures in April, and decays in May. Besides the warm-core feature, it also has an inherent low-salinity property, so it is named "spring mesoscale high (SMH)". Though with clear interannual variation in terms of intensity and spatial coverage, the SMH always emerges in the region between 110 E and 114 E and between 12 N and 16 N. The formation of SMH is ascribed to the combined effects of wind forcing and releasing of potential energy set up by winter monsoon. In particular, the wind-stress curl plays an important role in its development, maintenance, and dissipation.     

灰色预测在地下水位预测中的应用

针对小南海泉域地下水位的预测影响因素多,数据量少,不确定性较大的特点,本文由实测的数据按照井号,每月为一组,由方差的已定范围来选择置信度,并求出灰度值,从而得出,灰色理论适用于地下水位的预测。然后,用GM(1,1)为预测模型对小南海泉域的地下水位进行了预测,每四个数据一组得到预测数据,对比原始数据与预测数据,其变化趋势基本一致,误差在允许范围内,用GM(1,1)模型进行地下水位的预测,能够得到较为准确的预测结果,可以应用于实际的预测工作。     

兰村泉域地下水污染原因及可持续开发利用对策研究

为确保兰村泉域地下水资源的可持续开发利用,在现场踏勘及有关资料分析的基础上,对泉域地下水污染原因进行了研究。结果表明,兰村泉域地下水污染与以下因素有关:(1)污染物入渗;(2)地下水开采;(3)水环境化学条件变化;(4)部分地区地下水原生本底值异常。提出了泉域地下水可持续开发利用对策。研究成果为兰村泉域地下水资源保护与管理提供科学依据。