ALBERT

Description: Abstract Groundwater transit time is an essential hydrologic metric for groundwater resources management. However, especially in tropical environments studies on the transit time distribution (TTD) of groundwater infiltration and its corresponding mean transit time (mTT) have been extremely limited due to data sparsity. In this study, we primarily use stable isotopes to examine the TTDs and their mTTs of both vertical and horizontal infiltration at a riverbank infiltration area in the Vietnamese Mekong Delta (VMD), representative of the tropical climate in Asian Monsoon regions. Precipitation, river water, groundwater, and local ponding surface water were sampled for three to nine years and analyzed for stable isotopes (δ18O and δ2H), providing a unique data set of stable isotope records for a tropical region. We quantified the contribution that the two sources contributed to the local shallow groundwater by a novel concept of two‐component lumped parameter models (LPMs) that are solved using δ18O records. The study illustrates that two‐component LPMs, in conjunction with hydrological and isotopic measurements, are able to identify subsurface flow conditions and water mixing at riverbank infiltration systems. However, the predictive skill and the reliability of the models decrease for locations farther from the river, where recharge by precipitation dominates, and a low‐permeable aquitard layer above the highly permeable aquifer is present. This specific setting impairs the identifiability of model parameters. For river infiltration short mTTs (〈40 weeks) were determined for sites closer to the river (〈200 m), whereas for the precipitation infiltration the mTTs were longer (〉80 weeks) and independent of the distance to the river. The results not only enhance the understanding of the groundwater recharge dynamics in the VMD but also suggest that the highly complex mechanisms of surface‐groundwater interaction can be conceptualized by exploiting two‐component LPMs in general. The model concept could thus be a powerful tool for better understanding both the hydrological functioning of mixing processes and the movement of different water components in riverbank infiltration systems.

Description: Low water levels in the Great Lakes have recently had significant financial impacts on the region's commercial shipping, which transports hundreds of millions of dollars' worth of bulk goods each year. Cargo capacity is a function of a ship's draft, the distance between water level and the ship's bottom, and lower water levels force ships to reduce cargo loads to prevent running aground in shallow harbors and locks. Financial risk transfer instruments, such as index-based insurance contracts, may provide an adaptable method for managing these financial risks. In this work, a relationship between water levels and shipping revenues is developed and used in an actuarial analysis of the frequency and magnitude of revenue losses. This analysis is used to develop a standardized suite of binary financial contracts, which are indexed to water levels and priced according to predefined thresholds. These contracts are then combined to form hedging portfolios with different objectives for the shippers. Results suggest that binary contracts could substantially reduce the risk of financial losses during low lake level periods and at a relatively low cost of only one to three percent of total revenues, depending on coverage level. This article is protected by copyright. All rights reserved.

Description: Abstract The paper presents oxygen and hydrogen isotopes of 284 precipitation event samples systematically collected in Irkutsk, in the Baikal region (southeast Siberia), between June 2011 and April 2017. This is the first high‐resolution dataset of stable isotopes of precipitation from this poorly studied region of continental Asia, which has a high potential for isotope‐based paleoclimate research. The dataset revealed distinct seasonal variations: relatively high δ18O (up to –4‰) and δD (up to –40‰) values characterise summer air masses, while lighter isotope composition (–41‰ for δ18O and –322‰ for δD) is characteristic of winter precipitation. Our results show that air temperature mainly affects the isotope composition of precipitation, while no significant correlations were obtained for precipitation amount and relative humidity. A new temperature dependence was established for weighted mean monthly precipitation: +0.50‰/°C (r2 = 0.83; p 〈 0.01; n = 55) for δ18O and +3.8‰/°C (r2 = 0.83, p 〈 0.01; n = 55) for δD. Secondary fractionation processes (e.g. contribution of recycled moisture) were identified mainly in summer from low d excess. Backward trajectories assessed with the HYSPLIT model indicate that precipitation with the lowest mean δ18O and δD values reaches Irkutsk in winter related to moisture transport from the Arctic. Precipitation originating from the west/southwest with the heaviest mean isotope composition reaches Irkutsk in summer, thus representing moisture transport across Eurasia. Generally, moisture transport from the west i.e. the Atlantic Ocean predominates throughout the year. A comparison of our new isotope dataset with simulation results using the ECHAM5‐wiso climate model reveals a good agreement of variations in δ18O (r2 = 0.87; p 〈 0.01; n = 55) and air temperature (r2 = 0.99; p 〈 0.01; n = 71). However, the ECHAM5‐wiso model fails to capture observed variations in d excess (r2 = 0.14; p 〈 0.01; n = 55). This disagreement can be partly explained by a model deficit of capturing regional hydrological processes associated with secondary moisture supply in summer.

Description: Abstract Worldwide, aquifers in low‐lying coastal areas are threatened by saltwater occurrence, as a result of small head gradients, high groundwater abstraction rates and drain‐management of the landscape, which is likely to intensify with climate change. Numerical models can serve as tools to identify the sources of the salt and thus to increase understanding of the driving mechanisms and important parameters controlling the extent of saltwater intrusions. This way, areas vulnerable to sea level rise can be identified and managed. Challenges include unknown initial salt concentrations, heterogeneous geology, and anthropogenic alterations. In this study, hydrogeological, geophysical and geochemical data are used to develop a numerical density‐dependent groundwater flow and transport model with the objective to understand the history of a saltwater‐affected groundwater system and its likely response to historic and future changes. The extent of the simulated saltwater intrusion compares well with Airborne Electromagnetic data that show salt water up to 20km inland. The results reveal that the salt water originates from a combination of laterally intruding seawater and vertically infiltrating transgression water. Main features controlling the progression of the modern seawater into the coastal aquifers are high‐permeable, deep Miocene sand aquifers, buried valleys that provide preferential flow paths in combination with extensive Miocene clay layers that delay saltwater intrusion. Anthropogenic activity enhances the saltwater inflow from the ocean and induces transient conditions. Future scenarios show that saltwater progression due to non‐stationarity leads to enhanced contamination of the deeper aquifers. Climate change affects primarily the shallow aquifer systems.

Description: Abstract The utility of differentially mapping snow depth to assess snow water resources at the watershed scale has been demonstrated using snow free and snow on lidar surface elevations. On more limited spatial and temporal scales, the same principle has been successfully applied with the relatively new photogrammetric technique Structure from Motion (SfM). Given the low cost of cameras relative to lidar technology early studies are promising, yet it is well known that reconstructing elevations over bright snow surfaces in complex terrain has been a limitation for traditional photogrammetric methods. Therefore, before progressing to snow depth, it is worthwhile to constrain how well snow surface elevations are mapped with SfM. The lidar based Airborne Snow Observatory, which also has an RGB camera, provides a unique opportunity to assess SfM against coincidentally collected lidar. Here, we present a lidar‐SfM snow surface elevation comparison from the February 21st, 2017 flight, which took place in Senator Beck Basin, San Juan Mountains, CO, during the NASA SnowEx campaign (Year 1). After co‐registration of the two surface models the Normalized Median Absolute Deviation (NMAD) was 0.17 m with a mean relative elevation difference of 0.014 m at identical spatial resolution of 1m. The digital surface model (DSM) was created without the use of ground control points (GCPs), and shows a promising potential to apply SfM for watershed scale surface elevation and snow depth mapping, and warrants further investigation of SfM as a supplement or alternative to lidar.

Description: Hydropower on the Great Lakes makes up a substantial fraction of regional electricity generation capacity. Hydropower producers on the Niagara River (flowing between lakes Erie and Ontario) operate as run-of-river, and changing lake levels alter interlake flows reducing both generation and revenues. Index-based insurance contracts, wherein contract payouts are linked to lake levels, offer a tool for mitigating this risk. While a potentially useful tool, pricing of financial insurance is typically based on historical behavior of the index. However, uncertainty with respect to the impacts of climate change on lake level behavior and how this might translate to increased (or decreased) risk for those selling or buying the insurance remains unexplored. Portfolios of binary index-insurance contracts are developed for hydropower producers on the Niagara River, and their performance is evaluated under a range of climate scenarios. Climate Informed Decision Analysis is used to inform the sensitivity of these portfolios to potential shifts in long term, climatological variations in water level behavior. Under historical conditions, hydropower producers can use portfolios costing 0.5% of mean revenues to increase their minimum revenue threshold by approximately 18%. However, a one standard deviation decrease in the fifty year mean water level potentially doubles the frequency with which these portfolios would underperform from the perspective of a potential insurer. Tradeoffs between portfolio cost and the frequency of underperformance are investigated over a range of climate futures. This article is protected by copyright. All rights reserved.

Description: Measurements of water vapour flux from semi-arid perennial woodland (Mallee) were made for three years using eddy covariance instrumentation. There have been no previous long term, detailed measures of water use in this ecosystem. Latent energy flux (LE) on a half hourly basis was the measure of the combined soil and plant evaporation, “evapotranspiration” (E LE ) of the site. Aggregation over 3 years of the site measured rain (1136 mm) and the estimated evaporation (794 mm) suggests that 342 mm or 30% of rain had moved into or past the root zone of the vegetation. Above average rainfall during 2011 and the first quarter of 2012 (633 mm, 15 months) would likely have been the period during which significant groundwater recharge occurred. At times immediately after rainfall, E LE rates were the same or exceeded estimates of potential E calculated from a suitably parameterized Penman–Monteith (E PMo ) equation. Apparent free water E from plant interception and soil evaporation was about 2.3 mm and lasted for 1.3 days following rainfall in summer, while in autumn E was 5.1 mm that lasted over 5.4 days. The leaf area index (LAI) needed to adjust a wind function calibrated Penman equation (E PMe ) to match the E LE values could be back calculated to generate seasonal change in LAI from 0.12 to 0.46 and compared well with normalised difference vegetation index (NDVI); r = 0.38 and P = 0.0213* and LAI calculated from digital cover photography (DCP). The apparently conservative response of perennial vegetation evaporation to available water in these semi-arid environments reinforces the conclusion that these ecosystems use this mechanism to survive the reasonably common dry periods. Plant response to soil water availability is primarily through gradual changes in leaf area. This article is protected by copyright. All rights reserved.

Description: Measurements of water vapour flux from semi-arid perennial woodland (mallee) were made for 3years using eddy covariance instrumentation. There have been no previous long-term, detailed measures of water use in this ecosystem. Latent energy flux (LE) on a half hourly basis was the measure of the combined soil and plant evaporation, 'evapotranspiration' (E〈inf〉LE〈/inf〉) of the site. Aggregation over 3years of the site measured rain (1136mm) and the estimated evaporation (794mm) suggests that 342mm or 30% of rain had moved into or past the root zone of the vegetation. Above average rainfall during 2011 and the first quarter of 2012 (633mm, 15months) would likely have been the period during which significant groundwater recharge occurred. At times immediately after rainfall, E〈inf〉LE〈/inf〉 rates were the same or exceeded estimates of potential E calculated from a suitably parameterized Penman-Monteith (E〈inf〉PMo〈/inf〉) equation. Apparent free water E from plant interception and soil evaporation was about 2.3mm and lasted for 1.3days following rainfall in summer, while in autumn, E was 5.1mm that lasted over 5.4days. The leaf area index (LAI) needed to adjust a wind function calibrated Penman equation (E〈inf〉PMe〈/inf〉) to match the E〈inf〉LE〈/inf〉 values could be back calculated to generate seasonal change in LAI from 0.12 to 0.46 and compared well with normalized difference vegetation index; r=0.38 and p=0.0213* and LAI calculated from digital cover photography. The apparently conservative response of perennial vegetation evaporation to available water in these semi-arid environments reinforces the conclusion that these ecosystems use this mechanism to survive the reasonably common dry periods. Plant response to soil water availability is primarily through gradual changes in leaf area. © 2015 John Wiley & Sons, Ltd.