Rainstorm Characteristics Research Articles

Diurnal cycles of rain storms over South China during the presummer rainy season

The variation characteristics of rain storms (RSs) are closely related to complex internal physical processes and external dynamic and thermodynamic conditions. Using a 17-year observational rainfall dataset from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR), the diurnal cycles of various RS characteristics and their responses to the South China Sea Summer Monsoon (SCSSM) are investigated in South China (SC) during the presummer rainy season (PSRS). Before SCSSM outbreaks, the RSs in the western inland region of SC (WSC) have stronger precipitation intensities and convective features due to orographic lifting, especially at night, while those in the eastern inland region of SC (ESC) have higher RS occurrence frequencies with higher moisture transport, especially in the afternoon. The onset of the SCSSM leads to abundant moisture and sufficient convective available potential energy over the entire SC area, resulting in significant increases in the occurrence frequency, convective fraction, and precipitation top height of RSs. In the WSC, the weakened upward motion and smaller convective inhibition limit RS development, resulting in weaker rainfall intensity. In the ESC, a particularly unstable atmosphere and enhanced low-level moisture transport in the afternoon lead to a larger three-dimensional size, more active convection, and greater precipitation intensity in the RSs. These results offer fresh insight into the diurnal variation in rainfall during the PSRS and can be effectively used to evaluate numerical model simulations.

Statistical Analysis of Moisture Sources and Quantitative Contribution of Cold Vortex Rainstorms in Northeast China during the Warm Season

Abstract The northeast cold vortex (NECV) is an essential system in the northeast region (NER) of China. Understanding the moisture source and associated transport characteristics of NECV rainstorms is the key to the knowledge of its mechanisms. In this study, we focus on two NECV rainstorm centers during the warm season (May–September) from 2008 to 2013. The Flexible Particle (FLEXPART) model and quantitative contribution analysis method are applied to reveal the moisture sources and their quantitative contribution. The results demonstrate that for the northern NECV rainstorm center (R1), Northeast Asia (35.66%) and east-central China and its coastal regions (29.14%) make prominent moisture contributions, followed by R1 (11.37%), whereas east-central China and its coastal regions (45.16%), the southern NECV rainstorm center itself (R2, 17.90%), and the northwest Pacific (10.24%) principally contribute to R2. Moisture uptake in Northeast Asia differs between R1 and R2, which could serve as one of the vital indicators to judge where the NECV rainstorm falls in NER. Moisture from the Arabian Sea, the Bay of Bengal, and the South China Sea suffers massive en route loss, although these sources’ contribution and uptake are positively correlated with the intensity and scale of NECV rainstorms in the two centers. There exists intermonth and geographical variability in NECV rainstorms when the main moisture source region contributes the most. Regulated by the atmospheric circulation and the East Asian summer monsoon, the particle trajectories and source contributions of NECV rainstorms vary from month to month. Sources’ contribution also turns out to be diverse in the overall warm season.

Dynamic and thermodynamic characteristics of warm-sector rainstorms caused by the southwest china vortex in sichuan basin

Using automatic rainfall station and ERA5 reanalysis data, the Southwest China vortex (SWCV) processes that induce warm-sector rainstorms in the Sichuan Basin were analyzed, their environmental field and dynamic thermal characteristics were researched through physical diagnosis and dynamic synthesis, and the development mechanism was discussed. The results showed that for the warm-sector rainstorms caused by the SWCV (SWCV-WR), the general circulation backgrounds can could be divided into three types: upper trough-vortex (Type I), plateau shear line (Type II), and short-wave trough (Type III) types. Regarding the aspects of the maintenance of the SWCV, duration of the warm-sector rainstorms, and maximum hourly precipitation intensity, the influence of Type I is the most evident, followed by Types II and III for SWCV-WR. The vertical structure of the SWCV is shallow and inclined to the west with height, but the positive vorticity of Types I and II can reach up to 200 hPa for SWCV-WR. The pseudo-equivalent potential temperature in the vortex area is greater than 354 K, which is accompanied by an upward-energy tongue, and shallow secondary circulation occurs on the eastern side of the SWCV, promoting vortex development. Regarding the thermodynamic characteristics of SWCV, Type I is the strongest, followed by Type III, and Type II is the weakest. The water vapor supply in different types of SWCV-WR is not only closely related to the strength of water vapor transport in the Bay of Bengal, but also to the variations in water vapor transport caused by the influence of different water vapor sources, such as the South China Sea and western Pacific Ocean, during its transportation. For SWCV-WR, the vorticity advection presents an uneven east-west positive and negative distribution. Under the dynamic forcing, the positive vorticity on the east side of SWCV of Types I and II (III) is enhanced (weakened), while that on the west side is weakened (enhanced). Different atmospheric vorticity variations have different significant effects on the three types of SWCV-WR. Under the spatial non-uniform heating, the horizontal non-uniform heating effect on the different types of SWCV-WR has regional differences, while the vertical non-uniform heating effect has the largest effect on the spatial non-uniform heating and a positive heating effect on the three types of SWCV-WR. Therefore, the spatial non-adiabatic heating effect, particularly the vertical non-uniform heating effect, is an important mechanism for the development and evolution of SWCV and SWCV-WR.

Urban inundation response law analysis to characteristics of designed rainstorms based on coupled hydrodynamic and rainfall-tracking model

Extreme stormwater and high-impervious area, caused by climate change and high-urbanization, are widely considered as the essential factors for causing urban flood. Understanding the response law of urban inundation to characteristics of rainstorms is helpful to implement integrated flood mitigation measures. Therefore, this paper is focused on exploring the urban inundation response law based on designed rainstorms by coupled hydrodynamic and rainfall-tracking model. Pilot area of Guyuan sponge city, which is divided into 5 source areas, is adopted to conduct 36 types of rainfall scenario simulations with the combination of different rainfall amounts and durations as well as peak coefficients. Inundation analysis methods is used to obtain the relationship between maximum inundation maps and characteristics of rainstorms, and source tracking analysis method is novelty proposed to excavate the response law of the connectivity among source areas to characteristics of rainstorms. First, Results of inundation analysis reveal that rainfall amount, duration and peak value are the first, second and third critical rainstorm characteristics that determine the severity of disasters, the variation of inundation volume are 140 %, 30 % and 4.2 % when precipitation and duration as well as peak value double. Second, the inundation area that water depth more than 0.5 m increases quickly is the major reason that inundation volume varies with 2 times as the increasing of precipitation; the transferring runoff volume between source areas and land use reaches 0–6 % and 0–10 % of inundation volume. Third, SA 1 and 2 are the critical sub-areas to manage the runoff, when precipitation equals to 200 mm, SA 1 contributes 19.5–33.7 % of inundation volume in SA 2, and SA 2 contributes 28–30 % of inundation volume in SA 3. The study is helpful to further understand the response law of inundation and relationship among source areas to characteristics of rainstorms, provide novel insights for constructing integrated flooding intervention practices.

Evolutionary analysis of rainstorm momentum and non-stationary variating patterns in response to climatic changes across diverse terrains

This study aims to analyze time-series measurements encompassing rainstorm events with over a century of datasets to identify rainstorm evolution and dimensional transitions in non-stationarity. Rainstorm events are identified using partial duration series (PDS) to extract changes in rainstorm characteristics, namely maximum intensity (MAXI), duration (D), total rainfall (TR), and average rainfall intensity (ARI), in response to climate change. Ensemble empirical mode decomposition is used for trend filtering and non-stationary identification to explore spatiotemporal insight patterns. Trend models for the first–second-order moments of rainstorm characteristics are used to formulate the identified mean–variance trends using combined multi-dimensional linear-parabolic regression. Best-fitting combinations of various distributions (probability density functions) and trend models for multiple characteristic series are identified based on the Akaike information criterion. We analyze the dimensional transition in rainfall non-stationarity based on sensitivity analysis using PDS to determine its natural geophysical causes. The integrated methodology was applied to the data retrieved from nine weather stations in Taiwan. Our findings reveal rainstorm characteristics of “short D but high rainfall intensity” or “lower MAXI but high TR” across multiple stations. The parabolic trend of the first-order moment (i.e., mean) of ARI, D, and TR appears at the endpoint of the mountain ranges. Areas receiving monsoons and those on the windward plain show a rising parabolic trend in the first- and second-order moments (i.e., mean–variance) characterizing MAXI, implying that the occurrence frequency and magnitude of extreme MAXI increases. Non-stationary transitions in MAXI appear for mountain ranges exposed to the monsoon co-movement effect on both windward and leeward sides. Stations in the plains and rift valleys show upgraded and downgraded transitions in the non-stationary dimensions for D, respectively.

A Copula-based framework for joint encounter and state evolution analysis of urban short-duration rainstorm characteristics

In this study, in order to reveal the joint encounter and state evolution characteristics of urban short-duration rainstorms, a case study is conducted in Zhengzhou city, China. The joint probability distribution model of total rainfall (P) and peak rainfall (R) is constructed by using the Copula function, and their joint encounter and joint return period are analyzed. Additionally, the state evolution characteristics of P and R are explored by incorporating with the Markov chain. The results show that: (1) there is a good correlation between P and R under different rainfall durations. The Clayton Copula function is found suitable for 0.5 h and 1 h rainfall durations, while the Frank Copula function is selected for the 1.5 h rainfall duration. The P and R are more densely distributed in the joint probability interval of 0.2–0.7 and the joint return period of rainfall events (JRPRE) of 15-30freq, which are particularly sensitive to the changes in the corresponding intervals. (2) The probability of synchronous rich (F)-low (L) between P and R is greater than that of asynchronous F-L. The probability of synchronous F-L increases with longer rainfall durations, reaching the highest value of 74.92 % for the 1.5 h rainfall duration. (3) The transition probability and limit probability of the F/high (H) state and F-H combination state are relatively large, indicating that P and R exhibit strong self-conservation. These states are associated with the highest risk and tend to occur more frequently with shorter average return periods of rainfall events (ARPRE). The findings are valuable in uncovering the occurrence patterns of short-duration rainstorms and facilitating measures to mitigate waterlogging, thereby supporting urban sustainable development.

Landscape structures regulate the contrasting response of recession along rainfall amounts

Abstract. Streamflow recession, shaped by hydrological processes, runoff dynamics, and catchment storage, is heavily influenced by landscape structure and rainstorm characteristics. However, our understanding of how recession relates to landscape structure and rainstorm characteristics remains inconsistent, with limited research examining their combined impact. This study examines this interplay in shaping recession responses upon 291 sets of recession parameters obtained through the decorrelation process. The data originate from 19 subtropical mountainous rivers and cover events with a wide spectrum of rainfall amounts. Key findings indicate that the recession coefficient (a) increases while the exponent (b) decreases with the L/G ratio (the median of ratios between flow-path length and gradient), suggesting that longer and gentler hillslopes facilitate flow accumulation and aquifer connectivity, ultimately reducing nonlinearity. Additionally, in large catchments, the exponent (b) increases with increasing rainfall due to greater landscape heterogeneity. Conversely, in small catchments, it declines with rainfall, indicating that these catchments have less landscape heterogeneity and thus reduced runoff heterogeneity. Our findings underscore the necessity for further validation of how L/G and drainage area regulate recession responses to varying rainfall levels across diverse regions.

Analysis of the water‐vapor sources in rainstorm processes in Tianjin city based on the trajectory method

AbstractTianjin, one of the four municipalities in China, is the eastern gate of the capital city of Beijing and is of great socioeconomic importance. When rainstorms attack Tianjin, urban flooding often occurs due to the dense river network, well‐developed water system and flat terrain. In this study, the source analysis of water vapor in rainstorm processes in Tianjin during 2012–2020 is conducted based on the moisture source attribution method, and the PyTrajector and HYSPLIT softwares. Then, the evolution characteristics of rainstorms in Tianjin are investigated. The results show that the rainstorm water‐vapor sources in Tianjin city can be roughly divided into four directions. The west and southwest directions are the main source, which contribute about 89% of the water vapor to the rainstorms. For heavy rainstorm, the water vapor from the southwest direction contributes about 60%, which is larger than that of rainstorm. The southwest direction is the main water vapor source of heavy rainstorm in Tianjin and has the main effect on the water vapor fluctuations during heavy rainstorm. For the more hazardous extraordinary rainstorm, the water vapor from the southwest direction occupies an even larger proportion (74.3%). The annual total rainstorm precipitation in Tianjin city in 2012 was more than that in common years, and this is mainly due to the anomalous increase of water vapor from the southwest direction. This result further indicates that the annual total rainstorm precipitation in Tianjin is mainly influenced by the water vapor from the southwest direction. This study reveals that the majority of rainstorm in Tianjin originates from the western and southwestern directions, but significant heavy rainstorm events in Tianjin are particularly influenced by moisture from the southwestern direction. This research holds crucial implications not only for meteorological and water resource management in Tianjin but also provides valuable insights for global urban flood risk studies.

Impacts of rainstorm characteristics on flood inundation mitigation performance of LID measures throughout an urban catchment

The hydrological benefits of sponge city construction have sparked a variety of academic studies and discussions. However, the effectiveness of sponge city construction in mitigating flood inundation at the urban catchment scale remains rarely investigated. Therefore, the Jiaodong catchment in Zhenjiang City, which is a national sponge pilot city and has extensively implemented various LID measures, was selected as a study site. The SWMM-2DCA model was established and validated using measured rainfall and drainage pipe flow processes, as well as historical inundation-prone location records, and then applied to evaluate the accumulative effectiveness of LID measures in flood mitigation under different 2-hour design rainstorms with changing return periods (2, 5, 10, 20, and 30 years) and peak position coefficients (0.2, 0.5, and 0.8). The results revealed that nearly 90% of the inundated area had an inundation depth of less than 0.15 m, and the impact of rainstorm characteristics on the maximum inundation depth was very limited. Both the maximum inundation volume and area were positively related to the return period and the peak position coefficient of rainstorms. The increase in the rainstorm return period could advance the start of inundation and retard the occurrence of peak inundation. The maximum inundation volume and area could be significantly reduced by 63 ∼ 98% and 41 ∼ 96% respectively after the implementation of LID measures, but the average reduction rate for maximum inundation depth was only 3.7% for rainstorms with a return period longer than 10 years. This indicates that LID controls inundation better for volume and area than for depth. The changing patterns of absolute and relative reductions in maximum inundation volume and area with rainstorm characteristics exhibited reverse trends, while the absolute and relative reductions of maximum inundation depth demonstrated similar variations. The absolute reductions in both maximum inundation area and depth almost reached their extreme values at the 10-year rainstorm return period. The effects of LID on the timing of peak inundation depended largely on the peak position of rainstorms. These findings could contribute to a better understanding of the flood inundation mitigation performance of sponge city construction.

Spatial and Temporal Pattern of Rainstorms Based on Manifold Learning Algorithm

Identifying the patterns of rainstorms is essential for improving the precision and accuracy of flood forecasts and constructing flood disaster prevention systems. In this study, we used a manifold learning algorithm method of machine learning to analyze rainstorm patterns. We analyzed the spatial–temporal characteristics of heavy rain in Beijing and Shenzhen. The results showed a strong correlation between the spatial–temporal pattern of rainstorms and underlying topography in Beijing. However, in Shenzhen, the spatial–temporal distribution characteristics of rainstorms were more closely related to the source of water vapor causing the rainfall, and the variation in characteristics was more complex and diverse. This method may be used to quantitatively describe the development and dynamic spatial–temporal patterns of rainfall. In this study, we found that spatial–temporal rainfall distribution characteristics, extracted by machine learning technology could be explained by physical mechanisms consistent with the climatic characteristics and topographic conditions of the region.

Variation Characteristics of Rainstorms and Floods in Southwest China and Their Relationships with Atmospheric Circulation in the Summer Half-Year

Local climates are responding to global warming differently, and the changes in rainstorms in mountainous areas of Southwest China are of particular interest. This study, using monthly NCEP/NCAR reanalysis and daily precipitation observation of 90 meteorological stations from 1961 to 2021, analyzed the temporal and spatial variation characteristics of rainstorms and floods in Southwest China and their relationship with atmospheric circulations. The results led us to the following five conclusions: (1) Rainstorms and floods in southwest China mainly occur from June to August, during which time July has the most weather events, followed by August. (2) The southwest of Guizhou province, the southern edge of Yunnan province, and regions from the east of the Sichuan Basin to the north of Guizhou have experienced more rainstorms and floods, while the northwest regions of Southwest China have had fewer. (3) Over the last 61 years, rainstorms and floods have exhibited an overall rising trend, especially in the last 10 years. The year 2012 was an abrupt inflection point in rainstorms and floods in Southwest China, from low to high frequency, while the correlation coefficient between rainstorms and floods and the global surface temperature is above the 95% significance level. (4) Rainstorms and floods exhibit changes at periods of 8 years, 16 years, and 31 years. (5) Rainstorms and floods show a good correlation with multiple variables, such as South Asian high-pressure systems west of 90°E, the upper trough front, the northwest side of the western Pacific subtropical high, and the convergence of warm and wet air in the middle and lower layers with cold air on the ground.

The Space Conceptual Models and Water Vapor Characteristics of Typical Rainstorms during Plum Rain Season

Based on conventional observation data from the China Meteorological Administration (CMA) and reanalysis data from the American National Centers for Environmental Prediction and National Center for Atmospheric Research (NCEP/NCAR) between 2012 and 2021, combined with the meteorological analysis, composite synthesis, and water vapor trajectory analysis, the weather circulations of typical rainstorms during the 10 years can be divided into 4 categories: Static Front Pattern (SFP), Subtropical High Edge Pattern (SHEP), Northeast Cold Vortex Pattern (NCVP), and Low-Level Vortex and Shear Pattern (LLVSP). The SHEP and SFP rainstorms have the characteristics of long duration and wide range, while the NCVP rainstorms are characterized by mobility and disaster weather accompaniment. The daily precipitation of LLVSP cases has extremity feature. The occurrence and development of rainstorms are well coordinated with the systems on lower levels. The main water vapor channel in lower layers of the SFP cases is from the South China Sea, while it is from Bohai for the NCVP cases and the Bay of Bengal for the SHEP and LLVSP cases. The main water vapor channel in middle layers is from the Bay of Bengal because of the affection of the southwest air flow. The south boundary of the MLYRB is the most important water vapor input boundary, followed by the west boundary, while the East and North boundaries are the outflow boundaries. During the rainstorms, the low-level water vapor is exuberant with low-level water vapor convergence much stronger than the high-level divergence. Among the four types of rainstorms, the NCVP cases provide the most abundant low-level water vapor convergence, resulting in the strongest short-term precipitation among the four types. Combined with water vapor transportation and convergence, the refined spatial conceptual models of the four types of rainstorms can better judge the process intensity and falling area and provide reference for disastrous weather forecast and early warning.

Impacts of Rainstorm Characteristics on Runoff Quantity and Quality Control Performance Considering Integrated Green Infrastructures

Green infrastructure (GI) has been implemented globally to mitigate the negative effects of urbanization. GI also regulates the urban runoff process and reduces non-point source pollution by intercepting initial runoff pollution and stormwater storage. In this paper, the impacts on GI were quantified and analyzed, considering eight designed storms with a 24 h duration and eight others with a 2 h duration with the combination of two characteristics (return period and peak time). The runoff process and reduction effect of pollutants were simulated for GI combinations (green roofs, vegetative swale, bio-retention units, and permeable pavement) using the Storm Water Management Model, taking the Dongshan campus of Shanxi University as an example case study. The results show that the GI combination can reduce runoff, suspended solids (SS), and chemical oxygen demand (COD). For short- and long-duration rainstorms, the average reduction rates of runoff, SS, and COD were 39.7%, 38.8%, and 39.6%, and 36.5%, 31.7%, and 32%, respectively, indicating its better effectiveness for short-duration storms. The GI’s effect was more sensitive during the short-duration storms owing to the greater absolute value of the 2 h elastic coefficients versus that of the 24 h, and the best reduction effect was observed with a rainfall peak coefficient of 0.1. These results provide a scientific reference for GI planning and implementation under a changing climate in the future.

Spatiotemporal Evolution and Socioeconomic Impacts of Rainstorms and Droughts in Contiguous Poverty-Stricken Areas of China

To consolidate the achievements in the elimination of absolute poverty in China and prevent rural populations from returning to poverty as a result of meteorological disasters, this study analyzed the spatiotemporal characteristics of rainstorms and droughts and their socioeconomic impacts on China’s contiguous poverty-stricken areas (CPSAs) from 1984 to 2019. The annual number of rainstorms and drought days in CPSAs of China reached approximately 1.9 days/year and 44.6 days/year, respectively. It gradually decreased from southeast to northwest. Rainstorms showed a significant increasing trend of 0.075 days/decade, while there is no significant trend in drought days. Due to rainstorms and droughts, the average annual number of people affected and direct economic losses in CPSAs reached 34 million people/year and 29 billion Chinese yuan/year, accounting for 22.9% and 12.6% of China’s total amounts, respectively. The average annual loss rate due to disasters in this region reached 1.6%, which is 0.6% higher than the national level. Furthermore, the distinct features and socioeconomic impacts of rainstorms and droughts were identified on the southeastern and northwestern sides of the population density line (PDL) along Tengchong-Aihui in China. Droughts have often impacted the regions located along the PDL, while rainstorms and droughts have occurred more frequently in the regions to the southeast of the PDL than in the regions to the northwest of the PDL. As a result, the affected population and direct economic losses due to rainstorms and droughts in the regions to the southeast of the PDL were 8.8 and 9.2 times and 3.3 and 7.4 times higher, respectively, than those in the regions on the other side of the PDL. Although the losses were greater, the disaster resistance capabilities were significantly improved in these regions. In contrast, the regions to the northwest side of the PDL exhibited a significant increasing trend in losses with a relatively low disaster resistance capabilities. This study revealed that it is necessary to improve the capability of meteorological disaster prevention and reduction in China’s CPSAs, especially in the regions to the west of the PDL, which could further contribute to the realization of United Nations Sustainable Development Goals.

Climatic Change of Summer Rainstorms and the Water Vapor Budget in the Sichuan Basin

AbstractThis study aims to examine the variation of the characteristics of summer rainstorms and water vapor budget in the Sichuan Basin by using daily precipitation observation data and monthly mean ERA-Interim reanalysis data during 1979–2016. The results show that the spatial and temporal distribution of rainstorms in the Sichuan Basin is the result of the interaction between the special topography of the Sichuan Basin and different water vapor transports at low latitudes. The precipitation amount and frequency of rainstorms are mainly affected by the water vapor transports and budgets in different regions, and the intensity of rainstorms is mainly affected by the dynamic effects of regional and local topography, especially in the western and northern basin. The main reasons for the change of summer rainstorms in the Sichuan Basin include the atmospheric circulation over the key area of air–sea interaction in the tropical region, the anomalies of regional circulation, and water vapor transports in eastern China and the Sichuan Basin. A conceptual model for the summer rainstorm anomaly in the Sichuan Basin is proposed. With the establishment of consistent easterly airflow in the low-latitude tropical area (130°E–180°, 0°–10°N) and the anticyclone on its north, an anomalous southeasterly airflow and water vapor divergence maintain over eastern and southern China while an anomalous southeasterly airflow and water vapor convergence appear over the Sichuan Basin. So, more summer rainstorms occur in this region. Conversely, with the establishment of consistent westerly airflow in that same tropical area and the cyclone on its north, an anomalous easterly airflow and water vapor convergence maintain over eastern and southern China while an anomalous northeasterly airflow and water vapor divergence appear over the Sichuan Basin. So, fewer summer rainstorms occur in this region.Significance StatementRainstorm change in the Sichuan Basin has significant regional characteristics. This study aims to reveal the influence of regional variation of water vapor budget on summer rainstorms in the Sichuan Basin, which provides the important basis for the forecast of rainstorm in the Sichuan Basin, as well as new comprehension for the research and application of regional response to climate change. The amount and frequency of rainstorms are mainly affected by water vapor transports and budgets in different regions, and the intensity of rainstorms is mainly affected by the dynamic action of different regional and local topography. It reveals the new mechanism of multiscale interaction between the special topography of the Sichuan Basin and different water vapor transport in low latitudes.

An in-depth statistical analysis of the rainstorms erosivity in Europe

Heavy rainstorms play a central role in the water-driving soil erosion processes. An in-depth knowledge about temporal and spatial erosivity of rainfall events is required to gain a better understanding of soil erosion processes and optimize soil protection measures efficiency. In this study, the spatiotemporal distribution of more than 300,000 erosive events measured at 1181 locations, part of the Rainfall Erosivity Database at European Scale (REDES) database, is studied to shed some new light on the rainfall erosivity in Europe. Rainfall erosive events are statistically investigated through the Lorenz curve and derived coefficients such as the Gini coefficient (G). Additionally, seasonal characteristics of the most and the less erosive events are compared to investigate seasonal characteristics of rainstorms across Europe. The G shows largest values of inequality of the inter-annual temporal distribution of the rainfall erosive events in the Alpine region, mostly due to the large number of rainfall events with smaller rainfall erosivity. While for other parts of Europe, the inequality described by the G is mostly due to a small number of high erosive events. The G slightly decreases from south to north while no clear regional patterns can be detected. Additionally, in Europe, on average 11% (ranging from 1 to 24%) of all erosive events contribute to form 50% of the total rainfall erosivity. Furthermore, higher erosive rainfall events tend to occur later in the year compared to less erosive events that take place earlier. To our knowledge, this study is the first one addressing event scale rainfall erosivity distribution using more than 300,000 rainfall erosivity events and covering almost a whole continent. Scientifically our findings represent a major step towards large-scale process-based erosion modelling while, practically, they provide new elements that can support national and local soil erosion monitoring programs.

Spatiotemporal modelling of rainfall-induced landslides using machine learning

Natural terrain landslides are mainly triggered by rainstorms in Hong Kong, which pose great threats to life and property. To mitigate landslide risk, building a prediction model which could provide information on both spatial and temporal probabilities of landslide occurrence is essential but challenging. In this paper, real-time rainfall conditions are incorporated into landslide prediction through a unique rainstorm-based database of reported landslides. Other landslide controlling factors related to topography, geology, and land cover are also considered. Five machine learning methods, including logistic regression, random forest, adaboost tree, support vector machine, and multilayer perceptron, are utilized and compared. Validated against historical rainstorms, the machine learning powered landslide prediction model could reasonably forecast the occurrence of landslides in a spatiotemporal context. Moreover, the effects of different rainstorm characteristics in terms of distinct rainfall spatial distribution and intensity on landslide susceptibility could also be captured by this model. For the landslide controlling factors investigated, rolling rainfall factors are proven to play a more important role than antecedent rainfall factors for landslide prediction. Among the five machine learning methods, the random forest model yields the most promising results in terms of all performance indicators (i.e., classification accuracy, recall, precision, area under curve, and overall accuracy).

How do different sensors impact IMERG precipitation estimates during hurricane days?

Ground observation absence in many parts of the world highlights the importance of merged satellite precipitation products. In this study, we aim to evaluate the effect of different sources of data in the uncertainties of a merged satellite product, by comparing the Integrated Multi-satellitE Retrievals for GPM (IMERG) Final product (V06B) with a ground-based radar product, Multi-Radar Multi-Sensor (MRMS), using both pixel-based and object-based approaches. This study is focused on the eastern United States (land-only) during the hurricane days that occurred in 2016–2018. The results showed that IMERG had better agreement in terms of the average precipitation intensity and area with a bias reduction of 75% and 65%, respectively, when the passive microwave (PMW) sensor overpass is matched instantaneously with MRMS compared to temporally averaged MRMS data (MRMS-Averaged). PMW observations tend to show storms with smaller areas in the IMERG Final product in comparison with MRMS, possibly due to the effect of light precipitation not detected properly by PMW sensors. However, by removing the light precipitation (less than 1 mm/h) in the object-based approach, hurricane objects in the IMERG Final product tend to be larger during the PMW observations, which might be related to different viewing angles of sensors contributing to MRMS and IMERG products. Precipitation estimates have smaller areas with higher average intensity during the PMW observations in the IMERG Final product compared to data estimated by Morphed or IR (morph/IR) observations, which is probably related to the effect of morphing technique, leading to homogenization of the varying rainstorm characteristics. In addition, with the longer absence of PMW observations, the quality of morph/IR estimates in IMERG Final product deteriorates with a decreasing correlation coefficient, a growth in precipitation area and a downward trend in average precipitation intensity. Finally, the inter-comparison of PMW sensors showed the priority of imagers over sounders with GMI as the best among imagers and MHS as the best among sounders in terms of correlation and average intensity compared to MRMS; however, SSMIS was the best in capturing the precipitation area.

Spatio-temporal distribution of the rainstorm in the east side of the Helan Mountain and the possible causes of its variability

Compared with other arid areas, the convective rainstorm occurs more easily in the east side of the Helan Mountain, which is characterized by the short duration, large intensity, high precipitation efficiency and significant local distribution. In this paper, the 5-min and hourly precipitation at 512 regional automatic weather stations and other high-resolution observation data are used to analyze the spatio-temporal distribution and evolution characteristics of the rainstorm in the east side of the Helan Mountain during 2006 and 2019. Then, based on the daily precipitation data at 12 national observation stations, the rainstorm characteristics in this region during 1951 and 2005 are analyzed. On this basis, the rainstorm characteristics in the two periods are compared and studied. Finally, the possible causes of the distribution characteristics of rainstorm are initially discussed. The results show that the rainstorm with large magnitude and high intensity is mainly located in the mountainous region, and it mainly occurs in July with a high frequency period from afternoon to the first half of the night. Compared with 1951–2005, in 2006–2019 the rainstorm frequency, intensity and extremity are all increased, and the nocturnal and topographic features are more significant. The spatio-temporal distribution of rainstorm in the east side of the Helan Mountain is closely related to the nighttime enhancement of the low-level southeasterly jet and the interaction between the low-level jet and the mountainous topography. In the windward slope of the Helan Mountain, the interaction between the low-level jet and the mountainous topography could trigger or enhance the meso- and small-scale rainstorm systems, which would favor the occurrence of rainstorm. Overall, the conclusions in this study can deep the understanding of the rainstorms in the Helan Mountain, which could provide a reference for the monitoring and warning of rainstorms in this region.

Global rainstorm multi-attribute variation and its multiscale correlation with ENSO

This research uses a variety of statistical methods to diagnose the multi-attribute time series characteristics of global rainstorms and its response to ENSO from the perspective of land-ocean differentiation. The results showed that: (1) The global, global land and global ocean rainstorm and their contribution rates showed an increasing trend from 1979 to 2016. While, the global, global land and global ocean total rainfall showed an decreasing trend. The global land total rainfall showed a distinct sectional change pattern, which first increased from 1979 to 2006 and then decreased from 2007 to 2016. The comparison between the rainstorm and the total rainfall in global land and ocean showed that the rainstorm tended to increase in both ocean and land regions from 1979 to 2016, while the weak intensity rainfall tends to decrease in the globe. (2) The global land and ocean rainstorm and total rainfall did not change consistently on multiple time scales from 1979 to 2016, but showed inverse phase or forward and lag phase correlation. Fourthly, compared with ENSO, global land (ocean) rainstorm changed earlier (lag) in high energy spectral region. Compared with ENSO changes in low energy spectral region, global land rainstorm changes were consistent or ahead of time, while global ocean rainstorm changes were mainly ahead of time compared with ENSO changes.