Quantifying the hydrological processes governing flow in the unsaturated Chalk

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Drinking Water Salinity and Maternal Health in Coastal Bangladesh: Implications of Climate Change.

Background: Drinking water from natural sources in coastal Bangladesh has become contaminated by varying degrees of salinity due to saltwater intrusion from rising sea levels, cyclone and storm surges and upstream withdrawal of freshwater. Objective: Our objective was to estimate salt intake from drinking water sources and examine environmental factors that may explain a seasonal excess of hypertension in pregnancy. Methods: Water salinity data (1998-2000) for Dacope, in rural coastal Bangladesh, were obtained from the Centre for Environment and Geographic Information System. Information on drinking water sources, 24-hour urine samples and blood pressure were obtained from 343 pregnant Dacope women during the dry season (October 2009 - March 2010). The hospital-based prevalence of hypertension in pregnancy was determined for 969 pregnant women (July 2008 - March 2010). Results: Average estimated sodium intakes from drinking water ranged from 5 to 16 g/day in the dry season, compared to 0.6 - 1.2 g/day in the rainy season. Average daily sodium excretion in urine was 3.4 g/day (range 0.4 - 7.7 g/d). Women who drank shallow tubewell water were more likely to have urine sodium > 100 mmol/d than women who drank rainwater (OR=2.05, 95% CI: 1.11 - 3.80). The annual hospital prevalence of hypertension in pregnancy was higher in the dry season (12.2%, 95% CI: 9.5 - 14.8) than the rainy season (5.1%, 95% CI: 2.91 - 7.26). Conclusions: The estimated salt intake from drinking water in this population exceeded recommended limits. The problem of saline intrusion into drinking water has multiple causes and is likely to be exacerbated by climate change induced sea-level rise

Summary and synthesis of Changing Cold Regions Network (CCRN) research in the interior of western Canada – Part 2: Future change in cryosphere, vegetation, and hydrology

CCRN from the Natural Sciences and Engineering Research Council of Canada (NSERC) through their Climate Change and Atmospheric Research (CCAR) programPeer ReviewedThe interior of western Canada, like many similar cold mid- to high-latitude regions worldwide, is undergoing extensive and rapid climate and environmental change, which may accelerate in the coming decades. Understanding and predicting changes in coupled climate–land– hydrological systems are crucial to society yet limited by lack of understanding of changes in cold-region process responses and interactions, along with their representation in most current-generation land-surface and hydrological models. It is essential to consider the underlying processes and base predictive models on the proper physics, especially under conditions of non-stationarity where the past is no longer a reliable guide to the future and system trajectories can be unexpected. These challenges were forefront in the recently completed Changing Cold Regions Network (CCRN), which assembled and focused a wide range of multi-disciplinary expertise to improve the understanding, diagnosis, and prediction of change over the cold interior of western Canada. CCRN advanced knowledge of fundamental cold-region ecological and hydrological processes through observation and experimentation across a network of highly instrumented research basins and other sites. Significant efforts were made to improve the functionality and process representation, based on this improved understanding, within the fine-scale Cold Regions Hydrological Modelling (CRHM) platform and the large-scale Modélisation Environmentale Communautaire (MEC) – Surface and Hydrology (MESH) model. These models were, and continue to be, applied under past and projected future climates and under current and expected future land and vegetation cover configurations to diagnose historical change and predict possible future hydrological responses. This second of two articles synthesizes the nature and understanding of cold-region processes and Earth system responses to future climate, as advanced by CCRN. These include changing precipitation and moisture feedbacks to the atmosphere; altered snow regimes, changing balance of snowfall and rainfall, and glacier loss; vegetation responses to climate and the loss of ecosystem resilience to wildfire and disturbance; thawing permafrost and its influence on landscapes and hydrology; groundwater storage and cycling and its connections to surface water; and stream and river discharge as influenced by the various drivers of hydrological change. Collective insights, expert elicitation, and model application are used to provide a synthesis of this change over the CCRN region for the late 21st century

Assessing the effects of land surface representation on recharge simulated by models of varying complexity

Numerical models are frequently used for the quantification of groundwater recharge at the catchment scale. However, there is uncertainty as to the necessary level of detail with which the land surface needs to be represented. We compared four models that simulate recharge and represent the land surface with varying degrees of complexity. These models were: Penman-Grindley (PG), UN Food and Agricultural Organisation (FAO), SPAtial Distributed Evaporation (SPADE) and Joint UK Land Environment Simulator (JULES). The models were setup at four intensively monitored sites with different vegetation and soil types in two adjacent catchments. Standard parameter values were used to reflect how the models might be used by practitioners. The models were validated against soil moisture observations at all sites, as well as observed transpiration and interception over a year at a woodland site. The components of the simulated water balances were also compared at each site. Significant differences were noted in potential recharge between models at both grassland sites, although simulated average annual potential recharge varied by only 15 % at the grassland site on permeable soil. At the woodland sites, soil moisture contents were reproduced least accurately and there were large differences in potential recharge at both woodland sites. This predominantly resulted from varied and inaccurate simulation of evaporation, particularly in the form of interception losses where this was explicitly represented in models. Differences in model structure, such as runoff representation, and parameter selection also influenced the results

Mathematical modelling of pressure induced freezing point depression within soils exhibiting strong capillary pressure effect

Many geotechnical applications are affected by the melting and formation of ice in soils. Current state of practice involves incorporating the presence of ice within hydrological models for unsaturated soils using the so-called generalised Clapeyron equation [1]. This represents a modification of the conventional Clapeyron equation by allowing for the pressure in ice and liquid to be different at an ice-liquid interface. Such an idea has come about due to the effects of surface tension, which become important within the pores of porous materials such as soil and rock. However, a common assumption when using the generalised Clapeyron equation is that the ice pressure remains constant [2], which leads to unrealistic behaviour in the presence of significant pore-water pressure changes. Here we develop a new mathematical modelling framework to explore the impact of pressure induced freezing point depression within soils exhibiting strong capillary pressure effect. We solve the coupled mass and energy conservation problem using method of lines (e.g., [3]) with pressure and enthalpy as the primary dependent variables. Strong non-linear coupling develops through the chemical potential equation accounting for coexistence of ice and water in the presence of surface tension [5]. We present a sensitivity analysis showing how freezing point depression evolves within a porous block subject to temperature surface boundary cooling and varied capillary pressures

An efficient calibration technique for heat dissipation matric water potential sensors

Heat dissipation sensors are used to measure matric potential in soils. A van Genuchten equation can be used to fit the relationship between measured heat dissipation and matric potential. Calibration is required for each probe because of intrinsic variability in the properties of the porous material. However, calibration is time-consuming (months), requiring numerous measurements taken by a pressure plate apparatus over their operational range. Here the feasibility of minimizing the number of measurement points required to reliably characterize the calibration curve is explored. A two parameter (m = 1-1/n) and a three parameter (m is a free parameter) van Genuchten type model is used for the calibration. We explore how reducing the number of calibration measurement points impacts the resulting calibration curve, that is, what is the information content that each measurement provides, and how significantly is the calibration performance degraded by removing measurement points. We also consider how measurement errors during the calibration process, which are understood to be non-uniform over the range of matric potential values, result in uncertainty in the calibration curve, and explore how this uncertainty can be minimized. Different measurement locations (i.e., matric potential values) are found to contain different information content. A two-parameter-model calibration using four calibration points is recommended; and the specific location of these four points is essential to maximize the accuracy and the efficiency of the calibration. As a rule of thumb, the four points should be uniformly distributed on a log-scale over the pressure range from 20 to 1000 kPa

Toward an International Critical Zone Network-of-Networks for the Next Generation Through Shared Science, Tools, Data, and Philosophy

This workshop will bring together an international cohort of early career scientists to advance modes of collaboration across critical zone (CZ) networks, providing a foundation to do together what would be impossible to do alone. This will set the stage for how CZ science is done over the coming decades. Participants will learn about facilities/capabilities across networks, interoperable models, and cross-cutting science questions, including societal challenges involved in studying CZ. Participants will identify questions that can only be addressed by working across observatories, by leveraging existing capabilities and adding new dimensions. Explicit goals of this workshop are to:Facilitate cross-site and cross-network knowledge by synthesizing the scientific drivers, properties and processes studied, and instrumentation and modelling approaches used at different international CZO networks.Identify a subset of prioritized grand challenge questions drawn from recent lists developed through several community efforts (IAHS, AGU Hydrology, US CZO, US DOE Subsurface Biogeochemistry) and their crosswalk with a network of international field observatories.Launch an international early career network that will spearhead the next generation of cross-cutting CZ research to address prioritized grand challenges, promote open science approaches, and formulate recommendations to tackle the sharing of data, methods and ideas.Advance the collective knowledge by training attendees in topics such as: data discoverability, use of automated sensors, and “simple”, flexible models that require few parameters that can be used across this international network to address long standing CZ questions.Using workshop as platform to help facilitate coordinated, transdisciplinary investigations of the critical zone, identify next steps for the workshop. Straightforward examples could entail planning for subsequent collaboration efforts, white papers, or workshops. Longer-term plans could entail building a resource of lessons learned and best practices for new site development, establishing norms for open science and data sharing, and facilitating interactions between modelers, data scientists, and data generators