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Increased temperature rates have the potential to change the rainfall regime in a given region, as well as to intensify its extreme events, which may lead to significant and negative socioeconomic and environmental impacts on urban populations. However, knowledge about the extent of changes in rainfall rates in Rio de Janeiro City (RJC) remains incipient; thus, it is necessary applying indices climate change to help better understanding this phenomenon. The aim of the current study is to investigate changes in rainfall distribution and increase in the number of extreme rainfall events in RJC. Daily rainfall data deriving from fifteen weather stations distributed in RJC were analyzed in the RclimDex software and Mann–Kendall test. The analysis has shown increased rainfall rates from the beginning of the series to approximately the first ten years of study. Total rainfall rate has decreased after this period. Rainfall intensity in almost all seasons has decreased after 2005; this outcome has indicated reduced annual rainfall rate and number of wet days. However, there was prevalence of positive trends in daily rainfall rates (Rx1day) and in total rainfall of five consecutive days (Rx5day). The increased number of extreme rainfall events in RJC can cause sudden inundations, floods, runoffs and river overflows with potential to cause landslides and human death due to irregular occupation of hills and slopes.

This study investigates extreme rainfall episodes along the eastern foothills of the Taihang Mountains in North China from 30 July to 1 August 2023. It focuses on two types of extreme hourly rainfall rates (HRRs), i.e., the maximum regional-average HRR and site-observed HRR, which exhibited sequential development over southern, middle, and northern key regions. These rainfall extremes occurred in an environment where a high-pressure barrier over North China prevented the intrusion of cold air masses from the north while a northward-moving typhoon remnant vortex and its associated low-level jet (LLJ) transported warm and moist airflow from the south. Two distinct echo evolution modes and convection initiation mechanisms are identified for the two types of extreme HRRs. The maximum regional-average HRR occurred when the LLJ arrived to the east of the key regions, while the maximum site-observed HRR occurred when the warmer vortex center influenced the regions. Taking the northern key region as a representation, at the time of the maximum regional-average HRR, slantwise ascent of the airflow along a warm-frontal-like boundary released energy related to symmetrical instability, resulting in stratiform rainfall with weak convective cores. The transport of locally initiated convection over the eastern plain region, where the atmospheric stratification was more potentially unstable, also significantly contributed. When the maximum site-observed HRR occurred, the terrain lifting of warm and moist southeast airflow led to intense convection over the mountain foothills. Overall, the passage of the warm-core typhoon remnant vortex and interaction with Taihang Mountains determined the timing and location of extreme HRRs across the key regions.

Climate science has long explored whether higher resolution regional climate models (RCMs) provide improved simulation of regional climates over global climate models (GCMs). The advent of convective-permitting RCMs (CPRCMs), where sufficiently fine-scale grids allow explicitly resolving rather than parametrising convection, has created a clear distinction between RCM and GCM formulations. This study investigates the simulation of tropical-extratropical (TE) cloud bands in a suite of pan-South America convective-permitting Met Office Unified Model (UM) and Weather Research and Forecasting (WRF) climate simulations. All simulations produce annual cycles in TE cloud band frequency within 10–30% of observed climatology. However, too few cloud band days are simulated during the early summer (Nov–Dec) and too many during the core summer (Jan–Feb). Compared with their parent forcing, CPRCMs simulate more dry days but systematically higher daily rainfall rates, keeping the total rain biases low. During cloud band systems, the CPRCMs correctly reproduced the observed changes in tropical rain rates and their importance to climatology. Circulation analysis suggests that simulated lower subtropical rain rates during cloud bands systems, in contrast to the higher rates in the tropics, are associated with weaker northwesterly moisture flux from the Amazon towards southeast South America, more evident in the CPRCMs. Taken together, the results suggest that CPRCMs tend to be more effective at producing heavy daily rainfall rates than parametrised simulations for a given level of near-surface moist energy. The extent to which this improves or degrades biases present in the parent simulations is strongly region-dependent.

During the pre-summer rainy season, heavy rainfall occurs frequently in South China. Based on polarimetric radar observations, the microphysical characteristics and processes of convective features associated with extreme rainfall rates (ERCFs) are examined. In the regions with high ERCF occurrence frequency, sub-regional differences are found in the lightning flash rate (LFR) distributions. In the region with higher LFRs, the ERCFs have larger volumes of high reflectivity factor above the freezing level, corresponding to more active riming processes. In addition, these ERCFs are more organized and display larger spatial coverage, which may be related to the stronger low-level wind shear and higher terrain in the region. In the region with lower LFRs, the ERCFs have lower echo tops and lower-echo centroids. However, no clear differences of the most unstable convective available potential energy (MUCAPE) exist in the ERCFs in the regions with different LFR characteristics. Regardless of the LFRs, raindrop collisional coalescence is the main process for the growth of raindrops in the ERCFs. In the ERCFs within the region with lower LFRs, the main mechanism for the rapid increase of liquid water content with decreasing altitude below 4 km is through the warm-rain processes converting cloud drops to raindrops. However, in those with higher LFRs, the liquid water content generally decreases with decreasing altitude.

North China experienced devastating rainfall from 29 July to 1 August 2023, which caused substantial flooding and damage. This study analyzed observations from surface rain gauges and S-band dual-polarization radars to reveal the following unique features of the precipitation evolution from the plain to the mountains during this event. (1) The total rainfall was found concentrated along the Taihang Mountains at elevations generally > 200 m, and its spatiotemporal evolution was closely associated with northward-moving low-level jets. (2) Storms propagated northwestward with southeasterly steering winds, producing continuous rainfall along the eastern slopes of the Taihang Mountains owing to mountain blocking, which resulted in the formation of local centers of precipitation maxima. However, most rainfall episodes with an extreme hourly rainfall rate (HRR), corresponding to large horizontal wind shear at low levels, actively occurred in the plain area to the east of the Taihang Mountains. (3) The western portion of the extreme heavy rain belt in the north was mainly caused by long-lasting cumulus–stratus mixed precipitation with HRR < 20 mm h −1 ; the eastern portion was dominated by short-duration convective precipitation with HRR > 20 mm h −1 . The contributions of convective precipitation and cumulus–stratus mixed precipitation to the total rainfall of the southern and middle rain belts were broadly equivalent. (4) The local HRR maxima located at the transition zone from the plain to the mountains were induced by moderate storm-scale convective cells with active warm-rain processes and large number of small-sized rain droplets. (5) During the devastating rainfall event, it was observed that the rainfall peaked at around 1800 local time (LT) every day over the upstream plain area (no diurnal cycle of rainfall was observed in relation to the accumulated rainfall centers over mountain areas). This was attributable to convective activities along the storm propagation path, which was a result of the more unstable stratification with a suitable steering mechanism that was related to afternoon solar heating and enhanced water vapor. The findings of this study improve our understanding and knowledge of the extreme precipitation that can develop from the plain to the mountains in North China.

Event-based rainfall-runoff models are practical tools commonly used to predict catchments’ response to a rainfall event. However, one of the main concerns is that the characteristics of rain events are neglected in the model development. This paper develops a novel event-based rainfall-runoff equation to incorporate rainfall characteristics into account. The performance of the new equation is evaluated based on the root mean square error, Nash–Sutcliffe efficiency coefficient, and per cent bias for 13,339 rainfall-runoff events between 2005 and 2020 over 23 catchments across New Zealand and Australia with oceanic, mediterranean, tropical, subtropical, and semiarid climates. Compared to the previous event-based models, the new equation shows an improvement in runoff estimation in almost all case studies. Furthermore, considering the new equation is simple, efficient, and takes the rain event duration into account, the new equation has the potential to become a robust alternative method to the conventional curve number method in hydrological engineering projects.

The present study mainly focuses on the effect of temperature enhancement on local weather due to the heat emitted from anthropogenic sources with a numerical weather prediction model. In this study, anthropogenic heat (AH) flux is mainly considered as heat generated due to industrial action in the urban area. Angul district located between 20.41–21.80°N latitude and 84.55–85.30°E longitude in the Odisha state of India is chosen as the study region. In this location, a heavy rain event on 16 August 2008, and a light rain event on 22 March 2008 were identified. In the first part of this study, numerical simulations are performed using the mesoscale weather research and forecasting (WRF) model for both the rain events, based on which the near-surface rain rate is simulated. The simulated rainfall is compared against tropical rainfall measuring mission (TRMM) precipitation radar observations qualitatively for validation purposes. The comparative study throws a lot of insight based on different physics options available in the WRF model. The study found that the WRF double moment, 6-class microphysics scheme is better in capturing both the rain events in 2008. The TRMM validated WRF simulation now constitutes the control run against which comparisons for other cases are made. In the second part, a numerical experiment is performed to understand the effect of AH on local weather for the same region. The temperature at the surface level is perturbed by increasing it by 10 K near the industrial site and exponentially decreasing with a height up to the atmospheric boundary layer. The design of the numerical experiment is such that the sensible heat, latent heat and moisture parameters are affected by changing the temperature parameter alone. The result shows that the rainfall rate increases locally for both the events due to the increase in temperature at the industrial site. The rate of increase in heavy rain event is nearly twice whereas, in light rain, it was found to increase by 1.7 times. In the third and final part of the study, the flow pattern at the near-surface level is studied in and around the industrial zone, and the same is then compared with the perturbed case for both the rain events. In the perturbed cases, the difference in temperature in and around the region causes pressure differential leading to the formation of stronger wind.

Rain attenuation of radio waves with frequencies above 10 GHz causes a serious problem in wireless communications. For wireless systems design, highly accurate methods for estimating the magnitude of attenuation have long been studied. ITU-R recommends a calculation method for rain attenuation using R0.01, the 1 min rainfall rate that is exceeded for 0.01% of an average year. Accordingly, an R0.01 database suitable for this calculation has been constructed. In recent years, global warming has emerged as an important climatological issue. If the predicted rise in temperatures associated with global warming induces a significant effect on rainfall characteristics, the existing R0.01 database will need to be revised. However, there is currently no information for quantitatively evaluating the likely long-term change in R0.01. In our previous study, the long-term trend in annual maximum values for 1-day, 1 h, and 10 min rainfall in Japan was estimated from a large amount of meteorological data and a 95% confidence interval approach was used to identify an increasing trend of more than 10% over approximately 100 years. In this paper, we investigate the long-term trend in greater detail using non-linear approximations for three types of rainfall and adopt the Akaike Information Criterion to determine the optimal order of the non-linear approximation. The future trend of R0.01 is then estimated based on the long-term change in annual maximum 1 h rainfall, exploiting the strong correlation between long-term average annual maximum 1 h rainfall and R0.01.

This study investigates the effects of resolved deep convection on tropical rainfall and its multi‐scale variability. A series of aquaplanet simulations are analyzed using the Model for Prediction Across Scales‐Atmosphere with horizontal cell spacings from 120 to 3 km. The 3‐km experiment uses a novel configuration with 3‐km cell spacing between 20°S and 20°N and 15‐km cell spacing poleward of 30°N/S. A comparison of those experiments shows that resolved deep convection yields a narrower, stronger, and more equatorward intertropical convergence zone, which is supported by stronger nonlinear horizontal momentum advection in the boundary layer. There is also twice as much tropical rainfall variance in the experiment with resolved deep convection than in the experiments with parameterized convection. All experiments show comparable precipitation variance associated with Kelvin waves; however, the experiment with resolved deep convection shows higher precipitation variance associated with westward propagating systems. Resolved deep convection also yields at least two orders of magnitude more frequent heavy rainfall rates (>2 mm hr−1) than the experiments with parameterized convection. A comparison of organized precipitation systems demonstrates that tropical convection organizes into linear systems that are associated with stronger and deeper cold pools and upgradient convective momentum fluxes when convection is resolved. In contrast, parameterized convection results in more circular systems, weaker cold pools, and downgradient convective momentum fluxes. These results suggest that simulations with parameterized convection are missing an important feedback loop between the mean state, convective organization, and meridional gradients of moisture and momentum. Plain Language Summary Tall cumulonimbus clouds are abundant in the tropics. However, those clouds are so narrow and evolve so quickly that they cannot be captured by most weather prediction and climate models. Most of those models rely on a separate component, called a deep convection parameterization, to approximate the presence and evolution of cumulonimbus clouds and their associated processes. In this study, we use a specialized model that can use such a parameterization to approximate cumulonimbus clouds, or can explicitly produce those clouds without a parameterization given sufficient resolution. We then compare the characteristics of tropical weather systems from these two approaches. Our comparison shows that when the parameterization is used, the model produces lighter rainfall from circular clusters of clouds. Rainfall in these experiments happens only when there is enough water vapor and warming in the atmosphere to create clouds and rainfall. In contrast, when deep clouds are produced with fine resolution and no parameterization, the results are more realistic, with heavier rainfall organized into linear clusters of clouds. These results suggest that improvements to the representation of cumulonimbus clouds, either directly in the model or through improved parameterizations, would result in more accurate weather and climate predictions. Key Points Resolved deep convection yields more intense rainfall rates in the tropics—from the intertropical convergence zone to individual precipitation systems Equatorial waves appear at all horizontal resolutions, but their variability and intensity are stronger when deep convection is resolved Linear convective systems, resolved cold pools, and upgradient momentum fluxes explain the stronger rainfall with resolved convection

This study presents a comprehensive analysis of the microphysical structures of Meiyu heavy rainfall (near-surface rainfall intensity > 8 mm/h) across different life stages in the Yangtze-Huaihe River Valley (YHRV). We classified the heavy rainfall events into three life stages of developing, mature, and dissipating using ERA5 reanalysis and IMERG precipitation estimates, and examined vertical microphysical structures using Dual-frequency Precipitation Radar (DPR) data from the Global Precipitation Measurement (GPM) satellite during the Meiyu period from 2014 to 2023. The results showed that convective heavy rainfall during the mature stage exhibits peak radar reflectivity and surface rainfall rates, with the largest near-surface mass weighted diameter (Dm ≈ 1.8 mm) and the smallest droplet concentration (dBNw ≈ 38). Downdrafts in the dissipating stage preferentially remove large ice particles, whereas sustained moisture influx stabilizes droplet concentrations. Stratiform heavy rainfall, characterized by weak updrafts, displays narrower particle size distributions. During dissipation, particle breakups dominate, reducing Dm while increasing dBNw. The analysis of the relationship between microphysical parameters and rainfall rate revealed that convective heavy rainfall shows synchronized growth of Dm and dBNw during the developing stage, with Dm peaking at about 2.1 mm near 70 mm/h before stabilizing in the mature stage, followed by small-particle dominance in the dissipating stage. In contrast, stratiform rainfall exhibits a “small size, high concentration” regime, where the rainfall rate correlates primarily with increasing dBNw. Additionally, convective heavy rainfall demonstrates about 22% higher precipitation efficiency than stratiform systems, while stratiform rainfall shows a 25% efficiency surge during the dissipation stage compared to other stages.