Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale

Abstract

Mapping soil hydraulic parameters with traditional scaling methods that use laboratory-determined hydraulic characteristics (the LAB method) is not always feasible as it involves expensive, time-consuming and sophisticated measurements on soil samples collected in several locations of the study area. An alternative scaling method (the AP method) has been recently proposed to indirectly retrieve the soil hydraulic properties following the Arya-Paris physico-empirical pedotransfer function, which makes use of particle-size distribution and bulk density values. In this synthetic study we verify the performance of the AP method from a functional perspective, by evaluating the differences in the simulated soil water budget through a Monte Carlo approach. Notwithstanding that the AP method can provide soil hydraulic property patterns with faster experimental procedures and minor costs, we observe significant bias in the predicted spatially-averaged soil water budget due to a poor parametric calibration of the AP method and an imprecise identification of the spatial correlation structure of the AP-estimated scaling factors.

Citation Nasta, P., Romano, N., and Chirico, G.B., 2013. Functional evaluation of a simplified scaling method for assessing the spatial variability of soil hydraulic properties at the hillslope scale. Hydrological Sciences Journal, 58 (5), 1059–1071.     

Marsh benthic Foraminifera response to estuarine hydrological balance driven by climate variability over the last 2000 yr (Minho estuary,NW Portugal)

A high-resolution study of a marsh sedimentary sequence from the Minho estuary provides a new palaeoenvironmental reconstruction from NW Iberian based on geological proxies supported by historical and instrumental climatic records. A low-salinity tidal flat, dominated by Trochamminita salsa, Haplophragmoides spp. and Cribrostomoides spp., prevailed from AD 140–1360 (Roman Warm Period, Dark Ages, Medieval Climatic Anomaly). This sheltered environment was affected by high hydrodynamic episodes, marked by the increase in silt/clay ratio, decrease of organic matter, and poor and weakly preserved foraminiferal assemblages, suggesting enhanced river runoff. The establishment of low marsh began at AD 1380. This low-salinity environment, marked by colder and wet conditions, persisted from AD 1410–1770 (Little Ice Age), when foraminiferal density increased significantly. Haplophragmoides manilaensis and Trochamminita salsa mark the transition from low to high marsh at AD 1730. Since AD 1780 the abundances of salt marsh species (Jadammina macrescens, Trochammina inflata) increased, accompanied by a decrease in foraminiferal density, reflecting climate instability, when droughts alternate with severe floods. SW Europe marsh foraminifera respond to the hydrological balance, controlled by climatic variability modes (e.g., NAO) and solar activity, thus contributing to the understanding of NE Atlantic climate dynamics.     

Optimization of site exploration program for improved prediction of tunneling-induced ground settlement in clays

Excessive settlement caused by tunneling during construction often damages adjacent infrastructures and utilities. Such excessive settlement can also present a challenge in the maintenance of subways during their operation. Thus, it is important to be able to accurately predict tunneling-induced settlement. The uncertainties in geotechnical parameters, however, can lead to either an overestimation or an underestimation of the tunneling-induced settlement. Such uncertainties can arise from many sources such as spatial variability, measurement error, and model error; in this paper, the focus is on the geotechnical parameters characterization from site exploration. The goal here is to determine an optimal level of site exploration effort so that effective predictions of the tunneling-induced settlement in clays can be achieved. To this end, a Monte Carlo simulation-based numerical model of site exploration is first established to generate artificial test data. Then, a series of parametric analyses are performed to investigate the relationship between the level of site exploration effort and the accuracy of the tunneling-induced ground settlement prediction. Through the assumed different levels of site exploration effort, statistics of soil parameters are estimated using the maximum likelihood method and the tunneling-induced ground settlement is then analyzed using the probabilistic method, and finally the effect of site exploration effort is assessed. The knowledge generated from this series of analyses is then used to develop the proposed framework for selecting an optimal site exploration program for improved prediction of the tunneling-induced ground settlement in clays. Examples are presented to illustrate the proposed framework and demonstrate its effectiveness and significance.     

Intraseasonal variability of the surface zonal current in the equatorial Indian Ocean: Seasonal differences and causes

Using observations and numerical simulations, this study examines the intraseasonal variability of the surface zonal current(u ISV) over the equatorial Indian Ocean, highlighting the seasonal and spatial differences, and the causes of the differences. Large-amplitude u ISV occurs in the eastern basin at around 80°–90°E and near the western boundary at 45°–55°E. In the eastern basin, the u ISV is mainly caused by the atmospheric intraseasonal oscillations(ISOs), which explains 91% of the standard...     

Dynamics of seasonal and interannual variability of the ocean bottom pressure in the Southern Ocean

Seasonal and interannual variability of ocean bottom pressure(OBP) in the Southern Ocean was investigated using Gravity Recovery and Climate Experiment(GRACE) data and a Pressure Coordinate Ocean Model(PCOM)based on mass conservation. By comparing OBP, steric sea level, and sea level, it is found that at high latitudes the OBP variability dominates the sea level variability at seasonal-to-decadal time scales. The diagnostic OBP based on barotropic vorticity equation has a good correlation with t...     

Sea level rise along China coast in the last 60 years

Based on long-term tide gauge observations in the last 60 years, the temporal and spatial variation characteristics of sea level change along the coast of China are analyzed. The results indicate that the sea level along the coast of China has been rising at an increasing rate, with an estimated acceleration of 0.07 mm/a2. The rise rates were 2.4 mm/a, 3.4 mm/a and 3.9 mm/a during 1960–2020, 1980–2020 and 1993–2020, respectively. In the last 40 years, the coastal sea level has risen fastest in the South China Sea and slowest in the Yellow Sea. Seasonal sea levels all show an upward trend but rise faster in winter and spring and slower in autumn. Sea level change along the coast of China has significant periodic oscillations of quasi-2 a, 4 a, 7 a, 11 a, quasi-19 a and 30–50 a, among which the 2–3 a, 11 a, and 30–50 a signals are most remarkable, and the amplitude is approximately 1–2 cm. The coastal sea level in the most recent decade reached its highest value in the last 60 years. The decadal sea level from 2010 to 2019 was approximately 133 mm higher than the average of 1960–1969. Empirical orthogonal function analysis indicates that China’s coastal sea level has been changing in a north-south anti-phase pattern, with Pingtan and Fujian as the demarcation areas. This difference was especially obvious during 1980–1983, 1995–1997 and 2011–2013. The coastal sea level was the highest in 2016, and this extreme sea level event was analyzed to be related mainly to the anomalous wind field and ENSO.     

INTERANNUAL VARIABILITY OF WINTER AND SPRING PRECIPITATION IN SOUTH CHINA AND ITS RELATION TO MOISTURE TRANSPORT

The interannual variability of winter and spring precipitation in South China(SC)and its relation to moisture transport are investigated by using the monthly precipitation data of NMIC,NCEP reanalysis datasets and NOAA ERSST analysis datasets from 1960 to 2008.The results show that winter and spring precipitation in SC is less than normal from the 1960s to the start of the 1970s and from the end of the 1990s to the present.Most of rainfall anomalies on the whole regional scale of SC is well in phase during winter and spring,and the frequency of persistent drought is higher than that of persistent flood.Seasonal variations of moisture transport differences of SC between persistent drought and flood events are observed:the differences in winter are characterized by moisture transport from Bay of Bangle(BOB)and South China Sea(SCS),while differences in spring are characterized by that from SCS and North China(NC).There are two types of Ni o3.4 sea surface temperature anomaly(SSTA)related to persistent winter and spring drought(flood)events in SC,which are positive SSTA next to Ni o4(Ni o3)and negative SSTA next to Ni o3(Ni o4).Moreover,the variations of moisture transport from BOB and SC have important effects on persistent drought/flood in SC when the Ni o3.4 index is in the positive phase,while those from western North Pacific(WNP)-SC in winter and those from Philippine Sea(PHS)-SC and NC in spring primarily contribute to persistent drought/flood events in SC when the Ni o3.4 index is in the negative phase,and these stronger(weaker)moisture transports are observed in persistent flood(drought)during winter and spring regardless of the Ni o3.4 index.In conclusion,with the correlation between variations and distributions of Ni o3.4 SSTA and persistent drought/flood events in SC,moisture transport is responsible for the formation of precipitation anomalies.In addition,the moisture transport from SCS is most significantly correlated with persistent drought/flood events during winter and spring.     

The Super-large Ensemble Experiments of CAS FGOALS-g3

A super-large ensemble simulation dataset with 110 members has been produced by the fully coupled model FGOALS-g3 developed by researchers at the Institute of Atmospheric Physics, Chinese Academy of Sciences. This is the first dataset of large ensemble simulations with a climate system model developed by a Chinese modeling center. The simulation has the largest realizations up to now worldwide in terms of single-model initial-condition large ensembles. Each member includes a historical experiment (1850–2014) and an experiment (2015–99) under the very high greenhouse gas emissions Shared Socioeconomic Pathway scenario (SSP5-8.5). The dataset includes monthly and daily temperature, precipitation, and other variables, requiring storage of 275 TB. Additionally, the surface air temperature (SAT) and land precipitation simulated by the FGOALS-g3 super-large ensemble have been validated and projected. The ensemble can capture the response of SAT and land precipitation to external forcings well, and the internal variabilities can be quantified. The availability of more than 100 realizations will help researchers to study rare events and improve the understanding of the impact of internal variability on forced climate changes.     

The Asymmetric Atmospheric Response to the Decadal Variability of Kuroshio Extension during Winter

The Kuroshio extension(KE)exhibits interdecadal variability,oscillating from a stable state to an unstable state.In this paper,ERA-Interim reanalysis data are used to discuss the possible reasons for the asymmetric response of the atmosphere to symmetric sea surface temperature anomaly(SSTA)during periods of differential KE states.The analysis has the following results:the SSTA presents a nearly symmetrical distribution with opposite signs during the KE stable and unstable periods.During the KE stable period,the storm track is located north of 40°N and is significantly enhanced in the northeast Pacific Ocean.The atmospheric response is similar to the West Pacific/North Pacific Oscillation teleconnection(WP/NPO like pattern)and presents a barotropic structure.The inversion results of the potential vorticity equation show that the feedback of transient eddy vorticity manifests a WP/NPO like pattern and presents a barotropic structure,which is the main reason for bringing about the response of the WP/NPO like pattern.The magnitude of the feedbacks of both diabatic heating and transient eddy heating is small,which can offset one another.During the KE unstable period,the main body of the storm track is located to the south of 40°N,and there is no significant response signal in the atmosphere,except near the west coast of North America.Compared with the KE stable period,the asymmetry of response of the transient eddy vorticity is the main reason for the asymmetric response of the atmosphere.     

Understanding subsurface geological and geotechnical complexity at various scales in urban soils using a 3D model

The construction of a three-dimensional (3D) geological model to the scale of a city (greater Bordeaux area, France) has been undertaken, using several thousand boreholes and several hundred geotechnical tests on a more limited area. Data from some specific geographical areas have also been analysed for the purposes of professional applications related to geotechnical engineering, urban archaeology and asset management of buried networks. This paper focuses on the geotechnical dimensions, uncertainties and associated hazards. First, a geometrical model of the quaternary layer basis was built to the scale of the city, the variogram of which quantifies and models the anisotropic spatial correlation of this layer. Two specific studies were then made, as described in the following:

• modelling of the stratigraphy, to the scale of the city, in order to assess the depth and extent of the Flandrian formations. The thickness of these formations is directly linked to the staircase terraces of the Garonne river.

• on-site site analysis of an area where an infrastructure has suffered damage, resulting from large differential settlements, owing to its poor geotechnical properties. We show how geostatistical methods applied to in-situ or laboratory parameters can improve knowledge and understanding of the site, and can be useful in improving the settlement predictions which had been initially underestimated.