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Instantaneous precipitation can often cause devastating disasters on the Earth's surface. Continuous increases in extreme precipitation around the world have caused widespread concern, and it is necessary to study the extreme hourly precipitation over a large scale and long time series. Using specific numbers of unique hourly precipitation point data from 1980 to 2019, our research found that there are different spatial patterns regarding the frequency and intensity of extreme hourly precipitation in Mainland China, but the clear spatial pattern of being weak in the west and strong in the east of China. Most extreme hourly precipitation events occurred from June to August in the north of China and from April to October in the south of China. Afternoon and midnight are the peak periods of extreme precipitation events in southern China. The frequency of extreme hourly precipitation in the whole of China had increased by 0.7 hr/10a and increased significantly in the northwest and southeast of China. The average intensity of extreme hourly precipitation has decreased by 0.1 mm·hr−1/10a in the whole of China. While the maximum intensity has increased in local areas, the trend of changes is not significant in the whole of China. We have discovered that rapid urbanization is likely to be responsible for the frequency of extreme hourly precipitation in China. It is urgent to enact flood protection measures because this change is expected to worsen in the future with intensified urbanization in China. [ABSTRACT FROM AUTHOR]

Determining the effect of casting geometric structure on freckle formation is important in designing the directional solidification parameter of single‐crystal superalloy castings. In this research, single‐crystal castings of a third‐generation nickel (Ni)‐based superalloy with different thicknesses and structures are prepared by conventional Bridgman high‐rate‐solidification technique at withdrawal rates of 1, 3, and 6 mm min–1. The experimental results show that the freckles in castings with expansion structures are severer than those with contraction structures at a withdrawal rate of 1 mm min–1, and vice versa at withdrawal rates of 3 and 6 mm min–1. It is found that the larger casting thickness tends to promote the freckle formation at the same withdrawal rate. Furthermore, a lower tendency is displayed at the withdrawal rate of 3 mm min–1 in freckle formation, whereas an increased tendency is displayed at the withdrawal rate of 6 mm min–1. The different withdrawal rates, thicknesses, and structures of casting cause differences in cooling rate, shrinkage flow, and mushy zone morphology, which are believed to be responsible for the tendency of freckle formation. [ABSTRACT FROM AUTHOR]

Abstract: River flooding—the world's most significant natural hazard—is likely to increase under anthropogenic climate change. Most large rivers have been regulated by damming, but the extent to which these impoundments can mitigate extreme flooding remains uncertain. Here the catastrophic 2016 flood on the Changjiang River is first analyzed to assess the effects of both the Changjiang's reservoir cascade and the Three Gorges Dam (TGD), the world's largest hydraulic engineering project on downstream flood discharge and water levels. We show that the Changjiang's reservoir cascade impounded over 30.0 × 103 m3/s of flow at the peak of the flood on 25 July 2016, preventing the occurrence of what would otherwise have been the second largest flood ever recorded in the reach downstream of the TGD. Half of this flood water storage was retained by the TGD alone, meaning that impoundment by the TGD reduced peak water levels at the Datong hydrometric station (on 25 July) by 1.47 m, compared to pre‐TGD conditions. However, downstream morphological changes, in particular, extensive erosion of the natural floodplain, offset this reduction in water level by 0.22 m, so that the full beneficial impact of floodwater retention by the TGD was not fully realized. Our results highlight how morphological adjustments downstream of large dams may inhibit their full potential to mitigate extreme flood risk. [ABSTRACT FROM AUTHOR]

Desert greening through planting or irrigation is a potential approach to mitigate desertification and climate warming, but its influence on regional climate is unclear due to scarcity of observations. 'Desert blooms,' which are natural phenomena usually associated with the El Niño-Southern Oscillation, regularly occur in the world's driest desert, the Atacama Desert. This sudden conversion of land cover likely has a large impact on regional climate through alteration of local energy budgets and provides a unique opportunity to study the potential climatic and environmental consequences of desert greening. Here we evaluated the land surface effects of blooms in the Atacama Desert using vegetation and climate data acquired from remote sensing. The rapid vegetation growth during blooms led to an increase in evapotranspiration and a decrease in albedo. These two processes caused a 0.31°C ± 0.05°C decrease in daytime land surface temperature. During nighttime, we observed a 0.02°C ± 0.02°C increase in land surface temperature due to enhanced heat capacity associated with blooms. This asymmetric diurnal variation in land surface temperature produced a net decrease in daily land surface temperature of 0.29°C ± 0.07°C. Our observations demonstrate the potential benefits of desert blooms on local climate. Results from this study also provide new evidence for plausible climate consequences expected from local 'desert greening' strategies. [ABSTRACT FROM AUTHOR]

The digital elevation model data from traditional stereo photogrammetric methods are inadequate in providing accurate vertical parameters to feed hydrologic models for low-lying, extremely flat areas. High-resolution light detection and ranging (Li DAR) data provide the robust capability of capturing small variations in low-relief playa wetlands. The Rainwater Basin in south-central Nebraska includes a complex of seasonally shallow playa wetlands that attract millions of migratory waterfowl every spring and fall. This research focuses on the development of a procedure with applicable protocols to produce Li DAR-derived three-dimensional wetland maps and to extract the critical surface parameters (i.e., watershed boundaries, flow direction, flow accumulation, and drainage lines) for playa wetlands. The topo-hydrologic conditions of playa wetlands were evaluated at the watershed level. The results show that in the Rainwater Basin, 70.7% of the historic hydric soil footprints identified in the Soil Survey Geographic ( SSURGO) database were not functioning as topographically depressional wetlands. This finding was confirmed by a recent five-year Annual Habit Survey showing that 69.8% of the historic hydric soil footprints did not function during the spring migratory bird seasons between 2004 and 2009. The majority of playa wetlands' topographic conditions have been substantially changed and the SSURGO data cannot fully reflect current topographic reality in the Rainwater Basin. [ABSTRACT FROM AUTHOR]