Recent highlights across AGU Journals
This paper addresses a major challenge: anticipating or predicting groundwater solute transport behavior in realistically heterogeneous geologic media using knowledge of certain quantitative metrics about the system heterogeneity. In recent years, subsurface hydrologists have begun to recognize that not only is the variance of hydraulic conductivity (K) much larger than previously assumed in the literature, but that geologic processes and statistical physics (percolation theory) dictate that in 3D a relatively small percentage of the highest K facies will strongly tend to interconnect. While connectivity metrics have been used to partially characterize the subsequent effects on transport, no systematic way of characterizing the K variability, architecture and connectivity has yet emerged that helps one anticipate or predict transport behavior, including the heavy early- and late-time tails that cause both earlier than expected breakthrough and dramatically longer than expected solute retention in the system. The authors’ geological entropy approach is able to more effectively characterize subsurface heterogeneity to predict in advance the expected transport behavior in deposits.
This paper proposes an approach to addressing the issue of model structural error. Rather than seek diagnostic model correction, it uses the pragmatic approach of estimating a model of structural error to be used as a strategy for correcting the “biases” inherent to the model for a specific location. Meanwhile it places the estimation problem in the formal context of Bayesian inference, rather than one of the ad-hoc approaches proposed in the literature.
Snow is carried by wind, and snowdrifts often accumulate downwind of trees, a fence, a building, or a mountain ridge. Ohara  came up with a math equation that can determine the shape of the snow drift without the need for measurements of wind speed. This is useful when wind speed measurements are not available. Determining the shape of the snow drift allows scientists to better understand the physics related to how snow is moved by the wind at a certain location. The equation is useful since it could be used to design snow fences, which reduce blowing snow and increase visibility near roads. Snow fences are also used to make snow accumulate on fields so that the water from melting snow can help to grow crops. Also, the equation can be used with other equations to better predict the accumulation of snow in cold regions so that climate change, drought or flooding can be predicted. Snow accumulation on mountain ridges could be determined and used to make avalanche predictions. However, the math equation requires some inputs that are not easy to calculate and more research is required to determine the best way to find these inputs. More
A nationwide analysis of water use over the past 30 years finds that there is a disconnect between rural and urban areas, with most urban areas becoming more water efficient and most rural areas becoming less and less efficient over time.
“Understanding water use is becoming increasingly important, given that climate change is likely to have a profound impact on the availability of water supplies,” said Sankar Arumugam, a professor of civil, construction and environmental engineering at North Carolina State University in Raleigh and lead author of a new study on the work. “This research helps us identify those areas that need the most help, and highlights the types of action that may be best suited to helping those areas.”
The new paper in Earth’s Future, a journal of the American Geophysical Union, stems from a National Science Foundation-funded, interuniversity research project which focuses on understanding how water sustainability in the United States has changed over the past 30 years because of climate change and population growth…more
Growing plants and then storing the carbon dioxide they have taken up from the atmosphere is not a viable option to counteract unmitigated emissions from fossil fuel burning, a new study shows.
Plantations would need to be so large they would eliminate most natural ecosystems or reduce food production if implemented as a late-regret option in the case of substantial failure to reduce emissions, finds the new study in Earth’s Future, a journal of the American Geophysical Union.
However, growing biomass soon in well-selected places with increased irrigation or fertilization could support climate policies of rapid and strong emissions cuts to stabilize Earth’s climate below 2 degrees Celsius, according to the study’s authors…more
The authors of this paper use a coupled ocean-atmosphere General Circulation Model (GCM) to investigate oscillations in global average surface temperature and convective aggregation at steady state. They perform numeric simulations to show that the oscillations in temperature and aggregation are rather robustly phase locked, and that the period of oscillation is proportional to the assumed ocean mixed layer depth. They propose a plausible feedback mechanism and a simple analytic treatment to explain the numeric results. Radiative-Convective Equilibrium (RCE) has been a very useful theoretical tool to gain insight into the organization of the mean climate and climate change. This manuscript points out an interesting new application of this concept.
This type of deconvolution in paleoclimate climate model studies is only now becoming possible as computational capabilities increase and it is becoming easier to impose (large) boundary condition changes on simulations of past climates such as the Last Glacial Maximum. This study is an example of using a suite of model simulations to look at the model response to different impacts, and could be used as a template for future studies attempting to deconvolve the relative effects of different boundary condition changes on regional hydroclimate such as the North American Monsoon.
A new study from researchers at UCLA and the University of Houston reveals estimates of significant groundwater loss in California’s Central Valley during the recent drought and sparks questions of sustainability for the important agricultural area.
Researchers tracked net groundwater consumption in the Central Valley from 2002 to 2016, which included two droughts, one from 2007 to 2009 and the more severe drought from 2012 to 2016. California’s Central Valley is more than 18,000 square miles from the coast to the Sierra Nevada Mountains and is one of the largest agricultural hubs in the United States, providing more than half of America’s fruit, vegetable and nut crops…more
Since the mid-1980s, the percentage of precipitation that becomes streamflow in the Upper Rio Grande watershed has fallen more steeply than at any point in at least 445 years, according to a new study led by the National Center for Atmospheric Research (NCAR).
While this decline was driven in part by the transition from an unusually wet period to an unusually dry period, rising temperatures deepened the trend, the researchers said.
The study paints a detailed picture of how temperature has affected the runoff ratio — the amount of snow and rain that makes it into the river — over time, and the findings could help improve water supply forecasts for the Rio Grande, a water source for an estimated 5 million people…more
One million miles from Earth, a NASA camera is capturing unexpected flashes of light reflecting off our planet.
The homeward-facing instrument on NOAA’s Deep Space Climate Observatory, or DSCOVR, launched in 2015, caught hundreds of these flashes over the span of a year. NASA’s Earth Polychromatic Imaging Camera (EPIC) instrument aboard DSCOVR is taking almost-hourly images of the sunlit planet from its spot between Earth and the sun. In a new study, scientists deciphered the tiny cause to the big reflections: high-altitude, horizontally oriented ice crystals…more
The authors of this paper conduct calculations of fine mode aerosol acidity (pH) in northern China using a thermodynamic model constrained by observations of atmospheric acid and bases. They find that even under the highest levels of ammonia possible, the aerosol pH is less than 5, typically close to 4. This level of acidity suppresses potential multi-phase sulfur oxidation pathways recently suggested to explain missing sulfate sources in the region.
This paper seeks to get at the essence of what make slow (40-50) day weather in the tropics by simplifying the governing equations in a way that makes them solvable with pencil and paper. Specifically, the authors present a new model of linear equatorially trapped disturbances to a moist convecting atmosphere as a possible theory for some of the observed intra-seasonal variability of the tropics. It differs from previous similar models in exploring WISHE‐type (and possibly radiative) destabilization of moisture modes.
This paper demonstrates the value of using a nested large-eddy simulation methodology to capture fine-scale details tied to specific real-world conditions and locations. The authors have been very careful in their simulation setup, and document what should be considered best-practice approaches for doing this style of modeling. The overall finding of being able to capture the tail of the turbulence distribution for the nighttime stable conditions is also of considerable interest.
There are many similarities between the Qaidam Basin on the Tibetan Plateau and contemporary Mars. As such it can be used as an “environmental analogue”; these are locations that are useful in the study of other planets in order to interpret data received from rovers and landers and build a picture of planetary evolution. This paper describes geomorphological structures and mineral materials on the northwestern Tibetan Plateau that are comparable to those of Mars. The conditions of high altitude, high radiation, aridity, and salinity offer new opportunities for astrobiological research.
The North America Cordillera is one of the most-studied mountain belts in the world. There has been a dominant theory about its evolution for the last 40 years. This paper is the first substantial effort in a decade that involves the use of a geological data set to try to test different models of Cordilleran development. It takes account of a substantial set of paleomagnetic data that points to much of the orogen having been located thousands of kilometers south relative to cratonic North America as recently as 70 million years ago. As such, this is an important step in resolving the intractable issue of cordilleran development.
This Commentary discusses the possible processes that cause mixing of stream water and groundwater in the hyporheic zone in the light of literature on mixing processes and mixing controlled reactions in porous media and aquifers. The authors suggest new areas for research based on the observation that hyporheic zones mix more than would be expected based on groundwater flow theory. Understanding what causes hyporheic mixing is a relevant and timely research question as it could improve our ability to simulate and predict the attenuation of solutes in the hyporheic zone and, at the same time, allow for a more mechanistically informed interpretation of field results, for example, from stream tracer experiments.
The authors of this paper try to address a difficult problem of using satellite passive microwave data in differentiating first year from multiyear ice in the Arctic. The proposed method is a physically-based technique and the results demonstrate its superior performance over existing methods. This approach has an important application for retrieving sea ice emissivity at near real-time, which was not possible in previous studies or operations.
Retrieval of aerosol properties over complex surface conditions is a challenging task. The conventional approach usually requires making numerous assumptions about surface and aerosol properties. This study proposes a new approach to retrieve fine and coarse mode aerosol optical depth, soot particle fraction, and ground surface albedo by using multi-pixel and multi-channel satellite data. The paper has several case studies, both numerical and experimental, that confirm the importance of using multi-pixel information for retrieval, and the application of multi-pixel method to soot aerosol retrieval in the urban regions is interesting.
This paper provides insight into the complex rip current system under short-crested waves. It will improve the understanding of mixing and dispersion in the surf zone. More importantly, rip currents cause many drownings every year. Improving our predictive capability of rip currents will save lives.