Assessing distributed groundwater recharge rate using integrated surface water-groundwater modelling: application to Mihocheon watershed, South Korea

A method of estimating groundwater recharge, based on water-balance components using the SWAT-MODFLOW model (an integrated surface water-groundwater model), is described. A multi-reservoir storage routing module is suggested instead of a single storage routing module in SWAT; this represents a more realistic delay in the travel of water through the vadose zone. By using this module, the parameter related to the delay time can be optimized by checking the correlation between simulated recharge and observed groundwater levels. The final step of this procedure is to compare simulated groundwater levels as well as the simulated watershed stream flow with the observed groundwater levels and watershed stream flow. This method is applied to the Mihocheon watershed in South Korea to estimate spatio-temporal groundwater recharge distribution. The computed annual recharge rate is compared with the independently estimated recharge rate using BFLOW. The hydrologic modelling results show that the annual average recharge rate should be estimated by a long-term continuous simulation with a distributed hydrologic modelling technique.     

八达岭基性岩和高Ba—Sr花岗岩地球化学特征及成因探讨：华北和大别—苏鲁造山带中生代岩浆岩的对比

八达岭杂岩侵位于华北北部，由辉长闪长岩岩、石英闪长岩、石英二长岩、二长闪长岩、二长花岗岩、碱长花岗岩和石英正长岩等组成，主要属高钾钙碱性系列。除了含V-Ti磁铁矿的堆晶辉长闪长岩，整套岩石的主量元素变化范围较大，SiO2=46.5%-75.3%,MgO=5.6%-0.2%，中酸性岩石的K2O/NaO为0.59-1.09。碱长花岗岩和少数石英二长岩Ba和Sr含量较低，且具有明显（Eu）负异常。大多数中酸性岩石（高Ba-Sr花岗岩）具有如下显著的微量元素地球化学特征：Ba,Sr和轻稀土（LREE）富集，Y和重稀土（HREE）亏损，LREE/HREE强烈分离，Sr/Y和La/Yb比值较高；在原始地幔标准化的蛛网图中具有显著的Nb,Ta和Ti亏损，不具明显的Sr和Eu亏损。在Harker图解中，基性岩石和高Ba-Sr花岗岩的主量元素相关性明显，两者还具有相似的微量元素和稀土（REE）分配特征，并且，REE,Y,Sr,P和Ti含量从基性到酸性逐渐降低。辉长闪长岩和高Ba-Sr花岗岩的Sr-Nd同位素初始值呈EMI特征（Isr=0.7051-0.7068,εNdi=-8.2-20.2），大致呈负相关。地球化学特征表明基性岩浆为富集的大陆岩石圈地幔部分熔融形成，而高Ba-Sr花岗岩则为基性岩浆通过陆壳混染和结晶分离形成；富P和Ti的副矿物（如磷灰石和的榍石）的分离结晶导致了REE,P和Ti丰度的逐渐降低。另外，华北板块内部和大别-苏鲁造山带基性岩和高Ba-Sr花岗岩分别具有相似的地球化学特征，这表明，上述地区燕山期大规模岩浆活动具有相似的地球动力学机制，大别-苏鲁造山带岩浆岩的地球化学特征并不反映其地幔源区一定受到过来自深俯冲的扬子板块的流体的富集作用。岩石圈的拆沉和减簿作用可能导致了华北板块和大别-苏鲁造山带下古老岩石圈地幔的部分熔融，岩石圈地幔的富集作用可能主要性发生于元古代。     

The role of temperature in drought projections over North America

The effects of future temperature and hence evapotranspiration increases on drought risk over North America, based on ten current (1970–1999) and ten corresponding future (2040–2069) Regional Climate Model (RCM) simulations from the North American Regional Climate Change Assessment Program, are presented in this study. The ten pairs of simulations considered in this study are based on six RCMs and four driving Atmosphere Ocean Coupled Global Climate Models. The effects of temperature and evapotranspiration on drought risks are assessed by comparing characteristics of drought events identified on the basis of Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspration Index (SPEI). The former index uses only precipitation, while the latter uses the difference (DIF) between precipitation and potential evapotranspiration (PET) as input variables. As short- and long-term droughts impact various sectors differently, multi-scale (ranging from 1- to 12-month) drought events are considered. The projected increase in mean temperature by more than 2 °C in the future period compared to the current period for most parts of North America results in large increases in PET and decreases in DIF for the future period, especially for low latitude regions of North America. These changes result in large increases in future drought risks for most parts of the USA and southern Canada. Though similar results are obtained with SPI, the projected increases in the drought characteristics such as severity and duration and the spatial extent of regions susceptible to drought risks in the future are considerably larger in the case of SPEI-based analysis. Both approaches suggest that long-term and extreme drought events are affected more by the future increases in temperature and PET than short-term and moderate drought events, particularly over the high drought risk regions of North America.     

Derivation of regression coefficients for sea surface temperature retrieval over East Asia

Among the regression-based algorithms for deriving SST from satellite measurements, regionally optimized algorithms normally perform better than the corresponding global algorithm. In this paper,three algorithms are considered for SST retrieval over the East Asia region (15°-55°N, 105°-170°E),including the multi-channel algorithm (MCSST), the quadratic algorithm (QSST), and the Pathfinder algorithm (PFSST). All algorithms are derived and validated using collocated buoy and Geostationary Meteorological Satellite (GMS-5) observations from 1997 to 2001. An important part of the derivation and validation of the algorithms is the quality control procedure for the buoy SST data and an improved cloud screening method for the satellite brightness temperature measurements. The regionally optimized MCSST algorithm shows an overall improvement over the global algorithm, removing the bias of about -0.13℃ and reducing the root-mean-square difference (rmsd) from 1.36℃ to 1.26℃. The QSST is only slightly better than the MCSST. For both algorithms, a seasonal dependence of the remaining error statistics is still evident. The Pathfinder approach for deriving a season-specific set of coefficients, one for August to October and one for the rest of the year, provides the smallest rmsd overall that is also stable over time.     

Urbanization Effect on the Observed Change in Mean Monthly Temperatures between 1951-1980 and 1971-2000 in Korea

Gridded temperature data are necessary to run ecological models at regional scales for climate impact studies and have been generated by spatially interpolating measured values at synoptic stations. Because there are few synoptic stations with long-term records in rural areas in Korea, data from urban stations have been used for this purpose. Due to the overlapping of the rapid urbanization-industrialization period with the global warming era in Korea, climate data from these urbanized areas might be contaminated with urban heat island effect. This study was conducted to differentiate urbanization and regional climate change effects on apparent temperature change. Monthly averages of daily minimum, maximum, and mean temperature at 14 synoptic stations were prepared for 1951-1980 (past normal) and 1971-2000 (current normal) periods, respectively.Differences in two temperature normals were regressed to the logarithm of the population increase at 14 corresponding cities from 1966 to 1985. The regression equations were used to determine potential effects of urbanization and to extract the net contribution of regional climate change to the apparent temperature change. According to the model calculation, urbanization effect was common in all months except April. Up to 0.5° warming of nighttime temperature was induced by urbanization in the current normal period compared with the past normal period. There was little effect of regional climate change on local warming in the warm season (May through November). The cool season was warmed mainly by regionally increased daytime temperature. The results could be used to remove urbanization effects embedded in raw data, helping restore unbiased rural temperature trends in South Korea.     

Viscous fluid characteristics of liquefied soils and behavior of piles subjected to flow of liquefied soils

Lateral movement of sloping ground due to flow liquefaction has caused many pile foundations to fail, especially those in ports and harbor structures. Several researchers have found and verified that the behavior of liquefied soils can be simulated appropriately by modeling the liquefied soils as viscous fluid. In this study, the influence of the lateral movement of liquefied sloping ground on the behavior of piles was analyzed on the assumption that the flow of liquefied soils can be treated as viscous fluid flow. Sinking ball tests and pulling bar tests were performed to measure the viscosity of liquefied Jumoonjin sand. Then, the behavior of a single pile installed in liquefiable infinite slopes consisting of sand was investigated by numerical analyses. The liquefied sand behaved as non-Newtonian fluid, whose viscosity decreased with increasing shear strain rate. Furthermore, the flow of liquefied soils had a crucial effect on the stability of piles installed in the sloping ground.