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In conjunction with global warming, the frequency and intensity of typhoons in the Pearl River Estuary region are increasing annually, and coastal cities are becoming more vulnerable to compound disasters triggered by upstream flooding, typhoons, and astronomical tide surges, seriously threatening the lives and properties of people in the delta region. Quantitative analysis of the degree of variability of each factor associated with a compound flood event and accurate assessment of the magnitude of the compound flood event strongly impact the efficacy of coastal city responses aimed at disaster prevention and damage mitigation. In this study, focused on the Pearl River Estuary area, the tide levels at Sanzao station, wind speeds at Macao station, and daily maximum the maximum daily flow at Sanshui and Makou stations spanning 30 years from 1988 to 2017 were used to characterize the flood magnitude, typhoon magnitude, and astronomical tide magnitude of compound flood events in the Pearl River Estuary area. Data were screened using the annual maximum method. Based on the generalized additive model (GAMLSS) and the time-varying copula function, the encounter combinations of composite flood events of different levels and their main controlling factors were investigated. The results show that: 1) the main factors influencing initiation and magnitude of composite flood events in the Pearl River estuary area are non-consistent sequences that display interdependence. The time-varying copula model constructed in this study is more suitable for studies of composite floods than the traditional constant parameter copula model. Copula models are most applicable to studies of the encountered characteristics of multiple elements contributing to compound flood events and are most in line with actual situations. 2) Compared with the joint return period of traditional constant copula parameters, the period of occurrence of typical compound flood events in the Pearl River Estuary from 1988 to 2017 continuously shortens with time, the probability of occurrence increases, and the probability of future occurrence of extreme compound flood events is strengthening. The trend in which the return period of compound flood events is shortening with higher grades is accelerating. 3) Compound flood events throughout the Pearl River estuary area are more affected by typhoons and astronomical tides and less affected by water flow. When the return period of the three factors is one in 5 years, water flow causes the smallest increase in the co-occurrence return period; i.e., the influence of astronomical tide and typhoon on the scale of upstream flooding, composite flood events of typhoon, and astronomical tide is proportionately larger. Thus, composite flood events in the Pearl River estuary area are mainly impacted by typhoons with higher wind speeds. When the return period of the three factors is one in 10, 20, and 50 years, the increase in the co-occurrence return period caused by flow changes the most; and when the return period of the three factors is one in 10, 20, and 50 years, the acceleration of the co-occurrence return period caused by flow is the largest. When the three factors have a larger return period, astronomical tide exerts proportionately greater influence on the scale of the composite flood event of upstream flood, typhoon, and astronomical tide.

Understanding the transition from meteorological to hydrological drought is essential for accurately predicting hydrological droughts. However, the factors driving this transition are intricate, and a comprehensive understanding of how direct human activities influence this shift in drought is lacking. In this study, we initially explored the spatiotemporal correlation between the occurrence of meteorological and hydrological droughts. Subsequently, we formulated multiple hydrological replenishment scenarios using the soil and water assessment tool (SWAT) model to assess the environmental impact of the transition from meteorological to hydrological droughts. The Xijiang River Basin (XRB), the primary tributary of the Pearl River basin, was selected as the study area. Our results identified 91 meteorological droughts in the XRB, and only 66 hydrological droughts from 1978 to 2018. The transition rate from meteorological to hydrological drought demonstrated large spatial variability, with a basin‐average rate of 56% and the lowest transition rate of 45% in the headstream The transition from meteorological to hydrological drought was mostly rapid between November and December (~2 months), but can be prolonged during spring (about 3–5 months) and winter (around 7–9 months). Additionally, analysis of regeneration scenarios indicated that human activity has mitigated drought severity over recent decades. The primary driver affecting drought duration and frequency during the transition from meteorological to hydrological droughts shows conspicuous spatial disparities in densely populated areas. Although human activity significantly contributes to drought duration and severity compared to climate change during the transition in the headstream, its effects are more pronounced downstream in terms of drought duration and frequency. One plausible explanation is that increased water consumption downstream has considerably prolonged drought progression, whereas water management has counteractive effects on drought progression due to climate change in the headstream. Our findings offer valuable insights into the transition process from meteorological to hydrological droughts in the presence of extensive human activities. [ABSTRACT FROM AUTHOR]

As an advanced metal additive manufacturing technology, laser-directed energy deposition (DED-LB) has attracted a lot of attention in recent years, and is increasingly used in aerospace, automotive, marine, and biomedical applications. However, as industry application standards continue to improve, the challenges of part quality, process stability, and molding efficiency faced by DED-LB are becoming more and more prominent. On-line monitoring and real-time quality regulation can effectively avoid quality defects in processing, which is an effective measure to solve the problem. This paper summarizes the current research status of on-line monitoring means and closed-loop quality regulation technology for DED-LB. The on-line monitoring signals and related sensing devices mainly based on image signals, temperature signals, spectral signals, acoustic emission signals, and X-ray imaging, as well as the closed-loop control strategies and intelligent optimization methods in the process are discussed. Finally, a view on the future direction of on-line monitoring-control system for DED-LB is presented. [ABSTRACT FROM AUTHOR]

Sustainable management of blue and green water resources is vital for the stability and sustainability of watershed ecosystems. Although there has been extensive attention to blue water (BW) which is closely related to human beings, the relevance of green water (GW) for ecosystem security is typically disregarded in water resource evaluations. Specifically, there is a scarcity of comprehensive study on the detection and attribution of variation of blue and green water in the Dongjiang River Basin (DRB), an important source for regional water supply in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) of China. Here we assess the variations of BW and GW scarcity, quantify the impacts of climate change and land use change on BW and GW in DRB using a multi-water-flux calibrated Soil and Water Assessment Tool (SWAT). Results show that BW and green water storage (GWS) in DRB increased slowly with a rate of 0.14 and 0.015 mm a-1, respectively, while green water flow (GWF) decreased significantly at a rate of -0.21 mm a-1. The degree of BW and GW scarcity in DRB is low, and the per capita water resources in more than 80 % of DRB exceed 1700 m3 capita-1 a-1. Attribution results show that 88.0 %, 88.5 %, and 39.4 % of changes in BW , GWF , and GW S results from climate change, respectively. Both climate change and land use change have decrease BW , while climate change (land use change) decrease (increase) GW F in DRB. These findings can guide to optimize the allocation of blue and green water resources between upper reach and lower reach areas in DRB and further improve the understanding of blue and green water evolution patterns in humid regions. [ABSTRACT FROM AUTHOR]

Based on hourly precipitation data from 28 rainfall stations in the Pearl River Delta (PRD) region from 2001 to 2012, the accuracy of CMORPH, GPM and ERA5 is evaluated in the PRD on the annual, monthly and daily time scales by calculating 6 statistical metrics and exploring the frequency of different precipitation events. The results show that: (1) Compared with the three time scales of year, month and day, three products showed a highly positive correlation with the measured rainfall station on the monthly scale, but the correlation is weak on the annual and daily scales. (2) At the daily scale, all three precipitation products perform worse in the flood season than in the non-flood season. They are less accurate in detecting precipitation events in dry months than in other months, but the false alarm rate is higher in autumn and winter, and they all have a higher false alarm rate for stations near the coast than for inland stations. (3) In contrast, GPM can more accurately reflect the spatio- temporal trend and spatial distribution characteristics of precipitation in the PRD region. (4) Both CMORPH and GPM show high capacity to estimate various types of precipitation events, which can well reflect the contribution of the measured data to different types of precipitation events. Overall, GPM can best reflect the actual situation in the PRD region among the three products. [ABSTRACT FROM AUTHOR]