Water scarcity is rapidly increasing in many regions. In a novel, multi-model assessment, we examine how human interventions (HI: land use and land cover change, man-made reservoirs and human water ...use) affected monthly river water availability and water scarcity over the period 1971 - 2010. Here we show that HI drastically change the critical dimensions of water scarcity, aggravating water scarcity for 8.8%(7.4 - 16.5 %) ) of the global population but alleviating it for another 8.3 % (6.4 -15.8 %). Positive impacts of HI mostly occur upstream, whereas HI aggravate water scarcity downstream; HI cause water scarcity to travel downstream. Attribution of water scarcity changes to HI components is complex and varies among the hydrological models. Seasonal variation in impacts and dominant HI components is also substantial. A thorough consideration of the spatially and temporally varying interactions among HI components and of uncertainties is therefore crucial for the success of water scarcity adaptation by HI.
In this paper we present a multidecadal and global three‐dimensional stable water isotope data set. This is accomplished by incorporating processes of the stable water isotopes into an atmospheric ...general circulation model and by applying a spectral nudging technique toward Reanalysis dynamical fields. Unlike the global model simulations forced only by sea surface temperature (SST), the dynamical fields used in the simulation are never far from observation because the spectral nudging technique constrains large‐scale atmospheric circulation to that of observation, and therefore the simulated isotopic fields are reasonably accurate over the entire globe for daily to interannual time scales. As a case in point, it is revealed that the current approach reproduces the Arctic Oscillation much more correctly than the simulations forced only by SST, and consequently, the monthly isotopic variability better matches observations over midlatitudes to high latitudes in the Northern Hemisphere, especially Europe. This method is of great use in providing information in regions where in situ isotope observations are not available. Such information is required for a variety of biogeochemical, hydrological, and paleoclimate studies and as boundary and initial conditions for regional isotopic simulations.
Stable water isotopes in inland Antarctic ice cores are powerful paleoclimate proxies; however, their relationship with dynamical atmospheric circulations remains controversial. Using a water isotope ...climate model (MIROC5‐iso), we assessed the influence of the Last Glacial Maximum (LGM; ∼21,000 years ago) sea surface temperatures (SST) and sea ice (SIC) on Antarctic precipitation isotopes (δ18Op) through atmospheric circulation. The results revealed that the synoptic circulation mostly maintained southward moisture transport, reaching inland Antarctica. The steepened meridional SST gradient in the mid‐latitudes increased δ18Op in inland Antarctica with the enhanced baroclinic instability and synoptic moisture transport. In contrast, expanded SIC distribution decreased δ18Op over Antarctica by enhanced preferential removal of heavy isotopes during vapor transport due to the increased transport distance and enhanced surface cooling. These findings propose to use Antarctic ice cores to describe the southern hemisphere atmospheric circulation, represented by the westerly jets, during the LGM and other past climates.
Plain Language Summary
Stable water isotopes are widely used to reconstruct past variations of Earth's climate, such as the temperature in Antarctica during the Last Glacial Maximum (LGM) ∼21,000 years ago. This is an essential period for the climate community, given the order of magnitude of the temperature change between the LGM and today, which is similar to that of today's warming. However, the relationship between stable water isotopes and temperature is still subject to debate because of the influence of other climatic factors. Using an isotope‐enabled climate model, we found that the isotopic composition of Antarctic precipitation was not simply associated with the high and low average Antarctic temperature, but was substantially influenced by changes in dynamical atmospheric circulation related to sea surface temperature and sea ice expansion. We also suggest that representation of the past atmospheric circulations, such as westerly jets, can be constrained using water isotopic signals in Antarctic ice cores.
Key Points
Synoptic circulations sustained the moisture transport toward inland Antarctica
Meridional sea surface temperature gradient enhanced moisture and heavy isotope precipitations on Antarctica, unlike sea ice expansion
Antarctic ice core isotopes may refine southern hemisphere atmospheric circulations during the last glacial maximum
In this paper, we propose a method for regional analysis using image recognition technology based on deep learning and big data of street images captured by omnidirectional cameras on vehicles. ...Specifically, we first construct a classification method of regions based on street images using a pretrained deep learning model (VGG16) for image recognition as a feature extractor. Next, we develop a method to evaluate the landscape and safety of streets based on the ratio of street components (such as buildings, roads, fences, vegetations, sky, street lights) at each shooting point, which is calculated by semantic segmentation.
This paper examines the possibility of impression evaluation based on gaze analysis of subjects and deep learning, using an example of evaluating street attractiveness in densely built-up wooden ...residential areas. Firstly, the relationship between the subjects' gazing tendency and their evaluation of street image attractiveness is analysed by measuring the subjects' gaze with an eye tracker. Next, we construct a model that can estimate an attractiveness evaluation result using convolutional neural networks (CNNs), combined with the method of gradient-weighted class activation mapping (Grad-CAM) - these in in visualizing which street components can contribute to evaluating attractiveness. Finally, we discuss the similarity between the subjects' gaze tendencies and activation heatmaps created by Grad-CAM.
Six land surface models and five global hydrological models participate in a model intercomparison project Water Model Intercomparison Project (WaterMIP), which for the first time compares simulation ...results of these different classes of models in a consistent way. In this paper, the simulation setup is described and aspects of the multimodel global terrestrial water balance are presented. All models were run at 0.5° spatial resolution for the global land areas for a 15-yr period (1985–99) using a newly developed global meteorological dataset. Simulated global terrestrial evapotranspiration, excluding Greenland and Antarctica, ranges from 415 to 586 mm yr−1(from 60 000 to 85 000 km³ yr−1), and simulated runoff ranges from 290 to 457 mm yr−1(from 42 000 to 66 000 km³ yr−1). Both the mean and median runoff fractions for the land surface models are lower than those of the global hydrological models, although the range is wider. Significant simulation differences between land surface and global hydrological models are found to be caused by the snow scheme employed. The physically based energy balance approach used by land surface models generally results in lower snow water equivalent values than the conceptual degreeday approach used by global hydrological models. Some differences in simulated runoff and evapotranspiration are explained by model parameterizations, although the processes included and parameterizations used are not distinct to either land surface models or global hydrological models. The results show that differences between models are a major source of uncertainty. Climate change impact studies thus need to use not only multiple climate models but also some other measure of uncertainty (e.g., multiple impact models).
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
This paper proposes an improved method for converting a fine-resolution flow direction map into a coarse-resolution river network map for use in global river routing models. The proposed method ...attempts to preserve the river network structure of an original fine-resolution map in the upscaling procedure, as this has not been achieved with previous upscaling methods. We describe an improved method in which a downstream cell can be flexibly located on any cell in the river network map. The improved method preserves the river network structure of the original flow direction map and allows automated construction of river network maps at any resolution. Automated construction of a river network map is helpful for attaching sub-grid topographic information, such as realistic river meanderings and drainage boundaries, onto the upscaled river network map. The advantages of the proposed method are expected to enhance the ability of global river routing models by providing ways to more precisely represent surface water storage and movement.
To assess global water availability and use at a subannual timescale, an integrated global water resources model was developed consisting of six modules: land surface hydrology, river routing, crop ...growth, reservoir operation, environmental flow requirement estimation, and anthropogenic water withdrawal. The model simulates both natural and anthropogenic water flow globally (excluding Antarctica) on a daily basis at a spatial resolution of 1°×1° (longitude and latitude). This first part of the two-feature report describes the six modules and the input meteorological forcing. The input meteorological forcing was provided by the second Global Soil Wetness Project (GSWP2), an international land surface modeling project. Several reported shortcomings of the forcing component were improved. The land surface hydrology module was developed based on a bucket type model that simulates energy and water balance on land surfaces. The crop growth module is a relatively simple model based on concepts of heat unit theory, potential biomass, and a harvest index. In the reservoir operation module, 452 major reservoirs with >1 km3 each of storage capacity store and release water according to their own rules of operation. Operating rules were determined for each reservoir by an algorithm that used currently available global data such as reservoir storage capacity, intended purposes, simulated inflow, and water demand in the lower reaches. The environmental flow requirement module was newly developed based on case studies from around the world. Simulated runoff was compared and validated with observation-based global runoff data sets and observed streamflow records at 32 major river gauging stations around the world. Mean annual runoff agreed well with earlier studies at global and continental scales, and in individual basins, the mean bias was less than ±20% in 14 of the 32 river basins and less than ±50% in 24 basins. The error in the peak was less than ±1 mo in 19 of the 27 basins and less than ±2 mo in 25 basins. The performance was similar to the best available precedent studies with closure of energy and water. The input meteorological forcing component and the integrated model provide a framework with which to assess global water resources, with the potential application to investigate the subannual variability in water resources.
The aim of this research is to support the assessment of countries’ risks of water conflicts in the immediate future, considering their vulnerability to changes in water availability. The risk of ...international water conflicts in the 5 years ahead of the year of analysis was estimated based on current water availability and its unequal distribution. Countries were classified by their vulnerability to reductions in water availability. In these vulnerability groups, the links of water availability (TRIP discharges per capita) and its unequal distribution with the risk of water conflicts were explored. The Gini Coefficient was employed to measure the inequalities. Inequalities showed statistically significant positive Logit links with the risk of water conflicts. The greatest risk for volatile conflicts exists for the Asian, South American and African countries, having the lowest water availability and the lowest economic capacity. Increasing inequalities increases the likelihood of water conflicts, suggesting enhancing access to water, to lower the likelihood of water conflicts. South American and Congo River basin countries are only at risk of low-level water conflicts, but have higher risks of conflict escalation, when inequality increases. The risk of North American and Asian water conflicts were modeled well, except in western Asia. The water conflict estimation provided only 11.9 % under-estimations and an accuracy of 54.1 %, globally. Inequalities in water can indicate the risk of water conflicts in the above regions. However, the risk of water conflicts between countries with higher economic capacity in the European continent showed no link with inequality. This study will facilitate the estimation of the risk of water conflicts resulting from climate change.
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