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As a vital freshwater resource for one-sixth of the world's population, snowmelt provides great convenience for residents in terms of livelihood and production, agricultural irrigation, and hydroelectric power generation. However, snowmelt can also have an important impact on the formation of surface runoff and the process of soil erosion. In contrast to glacier melt, snowmelt erosion has received relatively little attention in the past. This paper reviewed the generation of snowmelt runoff, the characteristics of erosion and sediment yield during snowmelt, the snowmelt erosion mechanism, and the applications of snowmelt modeling. The published results of sediment yield driven from snowmelt runoff ranged from 1 to 300 t km−2 a−1, with the largest value of 1114 t km−2 a−1. Snowmelt erosion is extremely sensitive to warming climate. With global warming, there is a trend towards earlier snowmelt periods and a significant increase in runoff volume, as well as a significant increase in sediment yield from snowmelt in most of the study cases. Moreover, snowmelt erosion compared to rainfall erosion has more complex mechanistic processes which can be influenced by various factors such as snowfall, freeze-thaw, topography, etc. In particular, the occurrence of rain-on-snow events will lead to more severe soil erosion. In addition, current studies of sediment yield from snowmelt erosion account for a small percentage of snowmelt, and snowmelt erosion modeling is rarely applied in practical studies. In future research, the field monitoring of snowmelt erosion in the context of climate change needs to be further strengthened and the effects of multiple factors on snowmelt erosion need to be investigated. The inclusion of rain-on-snow and specific erosion types in the model will improve the applicability of models under climate change scenarios and in multi-scale environments. This paper is intended to show the achievements as well as the limitations of snowmelt erosion research, while suggesting future research directions that need to be further explored and developed for better understanding and forecasting of snowmelt erosion. [ABSTRACT FROM AUTHOR]

Radon can pose a serious risk on human health. At present, radon has been considered as the second leading cause of lung cancer after smoking. The potential risk of radon exposure in cold regions of Northern Hemisphere is increasing due to climate-induced permafrost degradation. In this paper, we took permafrost regions in the Northern Hemisphere as our study area. We performed an extensive literature review on the Web of Science (WoS), China National Knowledge Infrastructure (CNKI), and Google Scholar (GS). We divided these selected literatures into three groups: Group uranium, Group radon and Group permafrost and tried to reveal the impacts of distribution of uranium deposits/u-rich rocks and permafrost/permafrost degradation on radon concentration/migration in permafrost regions. Based our research, it is evident that uranium deposits or U-rich rocks provides an abundant source of U (Ra) for soils and groundwaters in permafrost regions, resulting in abnormally high concentrations of radioactive elements in soils and groundwaters. As a natural barrier, permafrost soils could screen the radon gas from migrating into underground dwellings and work-space in cold regions. However, permafrost degradation has been extensively observed and this trend is projected to continue under a warming climate. Permafrost degradation and ground ice melting, water exchange, gas emissions and thaw settlement have enhanced the ability of radon migration into dwellings and work space, which substantially endangers human health if long exposed. Our synthesis results also underline that the related research of radon migration and relation in permafrost regions are grossly inadequate and urgently needed. Research priorities include the mechanisms of radon migration in freezing, frozen, thawing and thawed soils/rocks, responses of release of radon sequestered in permafrost soils and radon migration in groundwater systems, among many others, to permafrost degradation. [ABSTRACT FROM AUTHOR]

Urban evapotranspiration (ET) is one of the most important components of water and energy balance, and carbon cycle in urbans. It is also a natural process that is powerful enough to possibly mitigate the negative effects caused by urbanization and global warming. Increasing or regulating urban ET could possibly be a solution to overcome the negative impacts caused by urbanization and global warming. Since 2000, researches on urban ET have been increasing and significant progresses have been achieved. A review of these progresses will certainly further promote the related researches and social practices, however, there is yet no such a review article available. Therefore, this article reviewed almost all the published papers on urban ET over the world, summarized its current progresses, scientific understandings, and forecasted the possible challenges in the future. Results achieved from this review would be helpful to use the power of ET to improve the livability of cities, guide the practices of sponge city construction and low impact development, mitigate the negative effect of urban heat island, and reduce urban carbon emission. [ABSTRACT FROM AUTHOR]

The Early 20th Century Warming (ETCW) in the northern high latitudes was comparable in magnitude to the present-day warming yet occurred at a time when the growth in atmospheric greenhouse gases was rising significantly less than in the last 40 years. The causes of ETCW remain a matter of debate. The key issue is to assess the contribution of internal variability and external natural and human impacts to this climate anomaly. This paper provides an overview of plausible mechanisms related to the early warming period that involve different factors of internal climate variability and external forcing. Based on the vast variety of related studies, it is difficult to attribute ETCW in the Arctic to any of major internal variability mechanisms or external forcings alone. Most likely it was caused by a combined effect of long-term natural climate variations in the North Atlantic and North Pacific with a contribution of the natural radiative forcing related to the reduced volcanic activity and variations of solar activity as well as growing greenhouse gases concentration in the atmosphere due to anthropogenic emissions. [ABSTRACT FROM AUTHOR]