Scientific challenges of research on natural hazards and disaster risk

As a discipline,the science of natural hazards and disaster risk aims to explain the spatial-temporal pattern,process and mechanism,emergency response and risk mitigation of natural hazards,which requires a multidisci-plinary and interdisciplinary approach.With the support of Natural Science Finance of China(NSFC)and Chinese Academy of Sciences(CAS),in-depth research and systematic analysis on natural hazards and disaster risk were conducted.In this paper,the state of the art in research on natural hazards is summarized from seven aspects:formation process,mechanism and dynamic of natural hazards,disaster risk assessment,forecast,monitoring and early warning,disaster mitigation,emergency treatment and rescue,risk management and post-disaster re-construction.The trends within the natural hazards and disaster risk as a discipline were identified,along with existing shortcomings and significant gaps that need to be addressed.This paper highlighted:1)the scientific challenges including the frontier scientific issues and technological gaps on natural hazards and disaster risk dis-cipline from 2025 to 2035 in China,and 2)the proposal to develop a systemic and holistic natural hazards and disaster risk discipline.

Desertification and Blown Sand Disaster in China

Approximately 331 million ha, one-third of China＇s total land, is prone to desertification processes, leading to natural disasters and economic losses. In this study, the situation, tendency, their influences and their risk governance of desertification and blown sand disaster in China were examined using satellite images, field photographs, field data and a literature review. The desiccated areas in Lop Nor and the lower Heihe River fluvial plain covered about 50,000 km2 and 40,000 km2, respectively. In Ejina, about 100 species of vegetation became extinct. The rate of wind erosion in China was between 1,000 tons/km2/year and 2,000 tons/km2/year. There were 12 sand deserts and sandy lands, occupying a total of 710,000 km2. Salinized soils occurred across 99.1 million ha. The two main sand and dust storm-prone areas in China were the Tarim Basin and its surroundings, and the Alxa Plateau and its surroundings. From 1981 to 2007, the annual average frequency of sand and dust storms varied from 1 d to 37 d with a general increase from southeast to northwest. Since 1978, China has implemented a number of ecological construction projects that have reduced desertification from 1999 to 2004 and from 2005 to 2009, and the number of dust and sand storm days from 9.3 d between 1954 and 1959 to 4.4 d between 2000 and 2007. The results could improve understanding of desertification and blown sand disasters in China and provide valuable experiences for global desertification control.

Wind erosion from crusted playa surfaces by no saltation and with saltation:A comparison through laboratory wind tunnel experiments

Playas are common in many arid regions and recognized as a major source of hypersaline particles.A better understanding of wind erosion on crusted playas has significant implications for land management and pollution control practices.We hypothesized that wind erosion rates of crusted playas were complicated and controlled by the interactions between playa crust and wind-induced saltation conditions.However,comparisons regarding the effects of different playa crusts on wind erosion under no saltation(NS)and with saltation(WS)conditions were lacking.In this study,laboratory wind tunnel experiments were carried out to simulate both NS and WS conditions,to investigate the erosion rates of different crust types(Salt,Takyr,and Puffic crust)at different wind speeds.Results showed that:1)Salt crust had greater crust strengths than did Takyr crust and Puffic crust;2)wind erosion rates under the WS condition were up to 60 times greater than those under the NS condition,suggesting that sand bombardment was the dominant mechanism responsible for removal of fine material from crusted playa surfaces;3)both sand bombardment rate and wind erosion rate of the playa crusts increased with increasing wind speed under the WS conditions;4)Puffic crust exhibited a greater rate of wind erosion compared to both the Takyr and Salt crusts under the Ns condition,yet tended to have a lower rate of wind erosion compared to both the Takyr and Salt crusts under the WS condition.This difference can be attributed to the fact that soft Puffic crusts are pliable and can dissipate the force of impacting grains under the Ws conditions.Our results indicated that wind erosion processes on crusted playas are complicated and are affected by wind-induced saltation and crust type,specifically crust strength and elasticityofthesurface.

Assessment of Building Physical Vulnerability in Earthquake‑Debris Flow Disaster Chain

Large earthquakes not only directly damage buildings but also trigger debris fows,which cause secondary damage to buildings,forming a more destructive earthquake-debris fow disaster chain.A quantitative assessment of building vulnerability is essential for damage assessment after a disaster and for pre-disaster prevention.Using mechanical analysis based on pushover,a physical vulnerability assessment model of buildings in the earthquake-debris fow disaster chain is proposed to assess the vulnerability of buildings in Beichuan County,China.Based on the specifc sequence of events in the earthquake-debris fow disaster chain,the seismic vulnerability of buildings is 79%,the fow impact and burial vulnerabilities of damaged buildings to debris fow are 92%and 28%respectively,and the holistic vulnerability of buildings under the disaster chain is 57%.By comparing diferent vulnerability assessment methods,we observed that the physical vulnerability of buildings under the disaster chain process is not equal to the statistical summation of the vulnerabilities to independent hazards,which implies that the structural properties and vulnerability of buildings have changed during the disaster chain process.Our results provide an integrated explanation of building vulnerability,which is essential for understanding building vulnerability in earthquake-debris fow disaster chain and building vulnerability under other disaster chains.

The 2023 Earthquake in Türkiye and Implications for China's Response to Catastrophe

On 6 February 2023,two 7.8 magnitude earthquakes consecutively hit south-central Türkiye,causing great concern from all governments,the United Nations,academia,and all sectors of society.Analyses indicate that there is also a high possibility of strong earthquakes with a magnitude of 7.8 or above occurring in the western region of China in the coming years.China is a country that is highly susceptible to catastrophic disasters such as earthquakes,floods,and other natural calamities,which can cause significant damages to both human life and property,as well as widespread impacts on the society.Currently,China's capacity for disaster prevention and control is still limited.In order to effectively reduce the impact of catastrophic disasters,ensure the safety of people's lives and property to the greatest extent possible,maintain social stability in high-risk areas,and ensure high-quality and sustainable regional development,it is urgent to improve the seismic resistance level of houses and critical infrastructure in high earthquake risk zones and increase the earthquake-resistant design level of houses in high-risk fault areas with frequent seismic activities;significantly enhance the ability to defend against extreme weather and ocean disasters in economically developed areas along the southeastern coast,as well as the level of fortification in response to extreme meteorological and hydrological disasters of coastal towns/cities and key infrastructure;vigorously enhance the emergency response capacity and disaster risk prevention level in western and ethnic minority regions;comprehensively improve the defense level of residential areas and major infrastructure in high geological hazard risk zones with flash floods,landslides,and mudslides;systematically promote national disaster prevention and mitigation education;and greatly enhance the societal disaster risk reduction ability,including catastrophic insurance.

Disaster Risk Science:A Geographical Perspective and a Research Framework

In this article,we recall the United Nations’30-year journey in disaster risk reduction strategy and framework,review the latest progress and key scientific and technological questions related to the United Nations disaster risk reduction initiatives,and summarize the framework and contents of disaster risk science research.The object of disaster risk science research is the"disaster system"consisting of hazard,the geographical environment,and exposed units,with features of regionality,interconnectedness,coupling,and complexity.Environmental stability,hazard threat,and socioeconomic vulnerability together determine the way that disasters are formed,establish the spatial extent of disaster impact,and generate the scale of losses.In the formation of a disaster,a conducive environment is the prerequisite,a hazard is the necessary condition,and socioeconomic exposure is the sufficient condition.The geographical environment affects local hazard intensity and therefore can change the pattern of loss distribution.Regional multi-hazard,disaster chain,and disaster compound could induce complex impacts,amplifying or attenuating hazard intensity and changing the scope of affected areas.In the light of research progress,particularly in the context of China,we propose a threelayer disaster risk science disciplinary structure,which contains three pillars(disaster science,disaster technology,and disaster governance),nine core areas,and 27 research fields.Based on these elements,we discuss the frontiers in disaster risk science research.

China’s Drought Disaster Risk Management: Perspective of Severe Droughts in 2009–2010

China has been frequently and heavily affected by drought disasters. During 2009–2010, three large-scale severe droughts struck China, caused considerable social, economic, and ecological losses. These droughts showed significant regional differences. This study employs a two-stage transition framework comprising “entry” and “exit” transitions to discuss disaster risk management of drought in China, by taking the three droughts as comparative case studies. Chinese society’s response in the exit transition is examined and the underlying factors that enable the entry trigger are diagnosed. The policy responses that lead to the exit transition from these drought disasters were appropriate, but there is substantial room for improvement in management strategy regarding both entry and exit transitions. This article suggests that government policies should emphasize entry-prevention measures that reduce adverse impacts early in a drought episode rather than focus solely on improving performance in achieving a rapid exit transition from drought.

Interaction among controlling factors for landslides triggered by the 2008 Wenchuan, China Mw 7.9 earthquake

The 12 May 2008 Mw 7.9 Wenchuan, China earthquake triggered about 200,000 landslides, which were controlled by a number of factors. This study examines five factors： slope angle, slope aspect, lithology, peak ground acceleration （PGA）, and fault side （relative position on the seismogenic fault, i.e., hanging wall or footwall）, to determine how these factors control the co-seismic land- slide occurrence and whether one or more factors, acting alone or in concert, are involved in promoting or suppressing landslides. We performed a multi-factor statistical analysis using data from the 2008 Wenchuan earthquake. The results show that in the areas characterized by steep topography or where strong ground shaking occurred during the earthquake, there is a closer relation- ship between slope aspect and landslide number density （LND） than other areas. The relationship between lithology and LND values depends on PGA. In turn, the relationship between LND values and PGA is also influenced by lithology. In addition, the controlling effect of lithology on co-seismic landslides on the hanging wall of the seismogenic fault is greater than that on the footwall. Examining interactions among these factors can improve understanding of the mechanisms of co-seismic landslide occurrence.

Pre‑rainy Season Rainstorms in South China—Risk Perception of the 11 April 2019 Rainstorm in Shenzhen City

With the acceleration of urbanization in South China, rainstorms and floods are threatening the safety of people in urban areas. The 11 April 2019(4·11 hereafter)rainstorm in Shenzhen City was a typical pre-rainy season rainstorm that caused great damage, yet such pre-rainy season events have not attracted sufficient attention in research.Risk perception of the public may indirectly affect their disaster preparedness, which is important for disaster management. In this study, we conducted a questionnaire survey that considered demographic factors and the level of risk perception, knowledge of risk, impact of the 4·11 rainstorm event on public risk perception, and degree of trust in the government. We used a two-factor model of risk perception to evaluate the factors that influenced public risk perception of the 4·11 rainstorm in Shenzhen. The main conclusions are: The 4·11 rainstorm improved public awareness of both risk and impact through the medium term, but the public’s perceived low probability of disaster occurrence and lack of knowledge of the pre-rainy season rainstorm phenomenon led to serious losses during this event. Although the public has high trust in the Shenzhen government, the management of rainstorm disasters in the pre-rainy season needs to be further improved.

Natural Factors Influencing Blown Sand Hazards in Beijing

In this article, natural factors in the farmingpastoral ecotone that might have influenced the blown sand hazards in Beijing in 2000 are analyzed. In the farmingpastoral ecotone, blown sand activities took place primarily in springtime, during which 39.8 percent of the annual frequency of erosive winds above threshold occurred. The prevailing directions of the erosive winds were NNW, NW, NWW, and N, with frequencies of 47, 20, 13, and 9 percent respectively. Sand entrainment and dust emission are influenced by erosive wind frequency, soil moisture, and land use and cover change. Favorable wind characteristics and a lasting drought in 1999 and 2000 may have produced ideal conditions for land surface desiccation, vegetation degradation, and land surface mobility and the occurrence of intense sand-and dust storms in Beijing.

Climate change and sandy land development in Qinghai Lake Watershed,China

The Qinghai Lake Watershed,containing the largest saline lake in northwest of China,has suffered from severe sandy land development in recent years.This paper analyzcs its daily precipitation,temperature,and wind from 1958 to 2001,and the spatial and temporal distributions of sandy land through the interpretation of remote sensing images covering four years(1977,1987,2000,and 2004).Results showed that since the middle of the 1960s,the daily precipitation(P)of 0<P≤5 mm decreased,while the P>20 mm increased significantly(S<0.05)in their annual total amounts and days.The maximum daily precipitation also increased significantly.Both the maximum dry spell and the total dry spell of more than ten days had a significant upward trend.Since the beginning of the 1960s,all the extremely high,extremely low and mean temperatures increased signifi-cantly(S<0.01),at a rate of 0.1℃/10a,0.2℃/10a,and 0.2℃/10a,respectively.The days with extremely high temperature had a significant upward trend,while the days with extremely low temperature had a significant downward trend.The Qinghai Lake was significantly shrinking(S<0.01)and provided abundant sediments for Aeolian erosion.The NNW wind prevailed in the watershed,and the largest scale wind was from the west and concentrated on the dry months.As a result,the sandy land was mainly born on the east bank of Qinghai Lake.The total sandy land area in the watershed had grown from 587.4 km^(2),660.7 km,697.6 km^(2) to.805.8 km^(2),accordingly,its area percentage growing from 2.0%,2.2%,2.4% to 2.7%,respectively.

Determination of erodible particles on cultivated soils by wind tunnel simulation

The erodible particle size distribution, diameter range and separate content of three soils from semi-arid regions of China were determined at different wind velocities through wind tunnel simulation and dry sieving. It was demonstrated that soil erodibility by wind depends not only on the intrinsic soil properties, but also on the extrinsic erosion effect of the erosive winds. It was supposed that there existed general consistency in the mechanics of wind erosion on different soils.