Evolution Of Rainfall Research Articles

Two Centuries of Monthly Rainfall in Barcelona (NE Spain): Disparity Trends, Correlation of Autumnal Rainfall with the WeMO Index and Its Contribution to Annual Amounts

Rainfall irregularity in Mediterranean regions is a characterizing feature of their climate. The aim of this manuscript is to analyze, in a climate change context, the evolution of this irregularity in Barcelona. A very long monthly database (1786–2023) enables detailed analysis of rainfall evolution, with its irregularity quantified using the concept of disparity, the trends of which are assessed using moving windows and a modified Mann–Kendall test. The relationship between disparity and the Western Mediterranean Oscillation index (WeMOi) is also explored. Additionally, the study compares rainfall amounts to the 1961–1990 reference period and evaluates autumn’s contribution to annual totals. A significant and increasing disparity trend over the years is detected for the autumn months. While correlations between disparity and WeMOi are limited, the WeMOi and monthly precipitation are significantly correlated for two autumn months, October and November, and for December, aligning with previous studies. This suggests the potential influence of the WeMOi fluctuations on future rainfall during these three months. Recent evidence of the increasing autumn irregularity is seen in the consecutive low-rainfall years of 2021, 2022 and 2023, which stand out as the driest since 1835, with the last two autumns ranking among the 5% driest.

Variability of seasonal temperature from 1990 to 2020 within Oum Er Rbia hydraulic basin (Morocco): Study of trends and anomalies

Abstract The fifth report of the Intergovernmental Panel on Climate Change (IPCC) indicates that global temperatures have increased during the 20th century. In Morocco, numerous studies have unveiled that the nation has been contending with the effects of global warming for several decades, attributed to its geographical location. The studies have mainly focused on the evolution of rainfall and the recurrence of droughts. Nevertheless, temperature variations remain less addressed, especially at large spatial scales. This paper aims to study the seasonal temperature variability in the large hydraulic basin of Oum Er Rbia, focusing on its anomalies and trends as well as identifying their impacts on the basin’s territory. Indeed, the large basin of Oum Er Rbia occupies more than 48,.000 km2 and is characterized by an arid to semi-arid climate. Its water resources are important and play an essential role in the country’s socio-economic development. This basin is well-known for its agricultural activity. Although its water and economic potential are significant, the great basin is considered vulnerable to climatic variations, which strongly condition its development. Considering the significance of temperature trends within the framework of global warming, this current study delves into the topic of seasonal temperature variability within the expansive hydraulic basin of Oum Er Rbia. Based on statistical analysis using the temperature anomaly index and the Mann-Kendall trend test, this study reveals that strong interannual variability marked the evolution of seasonal temperatures during the period of 1990-2020, with a remarkable upward trend during the autumn and spring. When the temperature increase, the temperature increases in turn: thus, the negative impacts affect both water resources and the agriculture sector, which suffers from the combined effect of increased evapotranspiration and reduction of irrigation water.

Impacts of Moisture Advection Scheme on Precipitation in the Steep Topography Region between the Tibetan Plateau and the Sichuan Basin

Abstract Water vapor transport is a crucial process in modeling and can contribute to errors in precipitation forecasts. To investigate the sensitivity of precipitation to the moisture advection scheme, this study introduced the two-step shape-preserving advection scheme (TSPAS), which has been proven to improve precipitation simulation over steep topography at lower resolutions, into the Southwest Center Weather Research and Forecast (WRF)-based Intelligent Numerical Grid Forecast System (SWC-WINGS) at a convection-permitting resolution. According to experiments conducted throughout the summer of 2021, the precipitation over the eastern slope of the Tibetan Plateau (TP) is highly sensitive to the moisture advection scheme. TSPAS successfully improved precipitation over the eastern slope of the TP, especially for torrential rainfall. The fractions skill score (FSS) is improved by 0.075 (27.78%) for daily precipitation with a threshold of 100 mm. Compared with the experiment with the original WRF advection scheme, the TSPAS reduced the overestimation of precipitation in the topographic region and excessive water vapor transport in a low-level atmosphere. To understand the precipitation improvement contributed by the advection scheme, additional experiments were conducted for a particular precipitation process from two approaches: switching advection schemes during the rainfall evolution and updating the variables related to moisture advection individually. Results demonstrate that the precipitation improvement is mainly contributed by the moisture advection scheme before the precipitation. Among the different variables, the combination of wind and water vapor was the most influential factor causing the precipitation improvement under the TSPAS.

A typology of subseasonal rainfall evolution during the southern Niger monsoon.

Niger is highly vulnerable to rainfall variability, often with adverse socioeconomic consequences. This study examined observed subseasonal rainfall variability during Niger's monsoon season (May to September). Using k-means clustering of dekadal (ten-day) rainfall, a typology was developed for the annual evolution of the monsoon season. Year-to-year rainfall variability for each of the first few dekads of the season is modest, but the middle, or peak of the rainy season demonstrates large interannual variability. Clustering analysis of annual timeseries for each dekad of the season revealed two types of monsoon progression. The distinction between the two types is strongly dependent on differences during the latter half of the season. For the first and third ten-day periods in August, and the first ten days in September, the two groups of years are more distinct. These results imply that while reliable prediction of the timing of anomalous onsets will be challenging, due to the relatively narrow range of uncertainty historically, there are opportunities for further exploration of dynamic and or statistical predictors or precursors using this typology that could potentially provide better information for decision-makers, especially with respect to agriculture.

Moist processes in NCUM global forecasts during the boreal summer monsoon

The objective of this study is to evaluate the performance of the National Center for Medium-Range Weather Forecasting Unified model (NCUM) global version in representing the moist processes during active and break monsoon periods over the Indian region. We employed the moist static energy (MSE) equation, a process-oriented diagnostic (POD), to examine the relationship between small-scale convection and large-scale circulation patterns in the forecast for eight monsoon seasons spanning from June to September 2015 to 2022. Results are validated by utilizing the European Center for Medium-Range Weather Forecasting Reanalysis (ERA5) data products. By employing PODs, we aimed to identify the influence of various MSE terms on rainfall evolution, particularly over the Central Indian (CI) region. We also investigated the systematic errors in certain processes that contribute to rainfall biases. Additionally, the study explored the moisture-convection relationship and compared the sensitivity of free tropospheric moisture to deep convection in the NCUM forecasts against the reanalysis data. The findings indicate weaknesses in the model's sensitivity to moisture and its ability to represent the rainfall-column water vapor (CWV) relationship highlighting areas where further improvements may be necessary to enhance the model's performance in monsoon forecasting. Despite the presence of systematic biases in the model's mean state of rainfall, such as dry biases over the Bay of Bengal and wet biases over the eastern Indian Ocean (EIO), the results obtained from the MSE diagnostics aligned with the existing understanding of monsoon dynamics. Specifically, the study emphasized the significance of horizontal advection of MSE as a leading term preceding the peak active/break conditions over the CI region. Hence, these findings not only showcase the usefulness of PODs in examining the strengths and weaknesses of numerical weather prediction (NWP) models but also serve as a verification tool for assessing model skills, leading to improved understanding and development of NWP models.

Northeastern Caribbean Rainfall Variability Linked to Solar and Volcanic Forcing

AbstractWe present a 500‐year precipitation‐sensitive record based on co‐varying speleothem δ18O values and Mg/Ca ratios from Larga cave in Puerto Rico. This multi‐proxy record shows that the evolution of rainfall in the northeastern Caribbean was characterized by alternating centennial dry and wet phases corresponding to reduced versus enhanced convective activity. These phases occurred synchronous with relatively cool and warm tropical Atlantic sea‐surface temperatures (SSTs), respectively. While the observed pattern suggests a close link of northeastern Caribbean rainfall to the Atlantic Multidecadal Variability, a regional comparison reveals intermittent regional heterogeneity especially on decadal timescales, which may be related to a superimposing influence of the Pacific and Atlantic basins. Furthermore, the speleothem‐based hydroclimate reconstruction indicates a significant volcanic impact during the past two centuries, and further reveals a potential solar signal in the preceding three centuries. We posit that the forcing likely shifted from solar to volcanic during the eighteenth century in being an important source of multidecadal to centennial Caribbean rainfall variability. The link between convective rainfall and natural forcing may be explained through a modulation of SST variations in the tropical Atlantic and Pacific oceans.

GAN-argcPredNet v2.0: a radar echo extrapolation model based on spatiotemporal process enhancement

Abstract. Precipitation nowcasting has important implications for urban operation and flood prevention. Radar echo extrapolation is a common method in precipitation nowcasting. Using deep learning models to extrapolate radar echo data has great potential. The increase of lead time leads to a weaker correlation between the real rainfall evolution and the generated images. The evolution information is easily lost during extrapolation, which is reflected as echo attenuation. Existing models, including generative adversarial network (GAN)-based models, have difficulty curbing attenuation, resulting in insufficient accuracy in rainfall prediction. To solve this issue, a spatiotemporal process enhancement network (GAN-argcPredNet v2.0) based on GAN-argcPredNet v1.0 has been designed. GAN-argcPredNet v2.0 curbs attenuation by avoiding blurring or maintaining the intensity. A spatiotemporal image correlation (STIC) prediction network is designed as the generator. By suppressing the blurring effect of rain distribution and reducing the negative bias by STIC attention, the generator generates more accurate images. Furthermore, the discriminator is a channel–spatial (CS) convolution network. The discriminator enhances the discrimination of echo information and provides better guidance to the generator in image generation by CS attention. The experiments are based on the radar dataset of southern China. The results show that GAN-argcPredNet v2.0 performs better than other models. In heavy rainfall prediction, compared with the baseline, the probability of detection (POD), the critical success index (CSI), the Heidke skill score (HSS) and bias score increase by 18.8 %, 17.0 %, 17.2 % and 26.3 %, respectively. The false alarm ratio (FAR) decreases by 3.0 %.

Chemical evolution of rainfall in China's first eco-civilization demonstration city: Implication for the provenance identification of pollutants and rainwater acid neutralization

Rainfall chemistry is a vital indicator for reflecting anthropogenic/natural input on atmospheric quality, and the rainfall process is also the main sink of air contaminants, which has received widely concerns by all walks of life. However, the chemical compositions, sources of major solutes, historical evolution, and their determinants of rainwater in Chinese urban area, which is hotspot of atmospheric pollutant emission, are unclear under the dual background of fast economic development and eco-civilization construction. To decipher these issues, the latest year data of observation-based rainwater chemistry and the historical rainwater data, and air pollution data of China's first eco-civilization demonstration city were integrated and studied. The results presented that SO42− (53.4 %) and NO3− (28.8 %), Ca2+ (46.5 %) and NH4+ (37.9 %) dominated the present rainwater anions and cations. The historical changes in the relative proportion of rainwater ions (e.g., the holistic decreasing trend of SO42−) revealed the reduction and management achievement of atmospheric pollutant emission driven by different stages of eco-civilization city construction. The atmospheric components were well removed by rainfall scouring and all the rainwater ions showed obvious temporal variations. The concentrations of most of ions were higher in winter but lower in summer due to the key factors of meteorological factor (mainly rainfall amount) and the seasonal variations of source contribution. The stoichiometry-based source identification and relative contribution calculation reflected that anthropogenic input was the most primary contributor of NO3− (99.4 %) and SO42− (95.4 %), and the contribution of fixed emission source was relatively higher than that of traffic sources. The NH4+ was defined as the anthropogenic input ion (urban wastes and fuel combustion), while all Cl− and Na+ were from oceanic input. In contrast, terrigenous input represented the most important origin of Ca2+, K+, and Mg2+, with relative contribution of 99.5 %, 97.0 %, and 90.7 %, respectively. The high neutralization factor (NF, about 2.0) values and neutralizing to acidifying potential (NP/AP, about 1.7) ratios and their increasing trend in past few decades revealed the fact of rainwater acid being highly neutralized under the background of eco-civilization city construction.

Characterization of Climate Change and Aquifer Recharge in Three Localities in the South-West of Côte d’Ivoire

Located in the southwestern part of Côte d'Ivoire, the study area's economic activity is rainfall-dependent agriculture and facing climate change impact on water resources. This study aims to improve the resilience of water users based on a better understanding of the recent manifestation of climate change. Specifically, it is to determine the episodes of rainfall variability and estimate the effective rainfall and groundwater recharge. The hydro-climatic database for this study covers more or less the period from 1977 to 2021. The characterization of rainfall variability was highlighted by the calculation of rainfall indices, while effective rainfall and recharge values were determined using the ESPERE (Estimation of Effective Rainfall and Recharge) software according to different mathematical methods. Using the non-parametric Pettitt test was possible to detect years with significant rainfall breaks. Thus, there was an alternation of deficit and surplus periods at different scales in the three localities. However, a break in the rainfall pattern occurred in 1989 in San Pedro, whereas this event took place a year later, in 1990, in the other two localities. The effective rainfall and annual recharge closely followed the rainfall evolution in the three localities at different scales. This acquired knowledge of hydrological and hydrogeological rainfall, dynamics can be used to better educate the resilience and climate change adaptation habits of the populations in the southwest region of Côte d'Ivoire.

Contamination characteristics in runoff fractions from a nuclear facility in São Paulo, Brazil.

The stormwater runoff may act as a nonpoint pollutant source and contributes to aquatic ecosystem quality decay in urban environments. The aim of this work was to evaluate the runoff characteristics on the transport of total solids and total metals, as well as pH and conductivity responses during the rainfall evolution. During 2017 and 2018, 12 rain events were monitored in 4 sampling stations at a car parking lot located at Nuclear and Energy Research Institute (IPEN/CNEN) in São Paulo/Brazil. A 4-chamber integrated collector allowed the sequential/temporal runoff evolution assessment. The runoff composition, in decreasing order of quantities, was Ca > K > Mg > Si > Al > Fe > Na > Zn > Mn > Sr > Ti > Mo > V > Cu > B > Pb > Ni > Ce > Sb > Cr > La > U > Th > Cd. The amount of total solids, Al, and Fe exceeded the Brazilian water quality standards. Principal component analysis (PCA) identified the elemental clusters linked to the facility activity, soil, and traffic/atmospheric-related deposition. The results show that the runoff characteristics could be differentiated by pollutant source. Factors such as seasonal variation, rain event intensity, air mass from oceanic or continental origin, spatial distribution inside the monitoring area, and the intensity of the first flush must be considered in order to disentangle the elemental clusters and pollution source contributions. In winter, continental air masses were associated with higher concentrations of heavy metals in the surface runoff. Spatial changes with no seasonal variation were observed for U, Th, La, and Ce.

Analysis Of The Spatial And Temporal Variability Of Rainfall In The Kayanga-Anambé Hydrological Complex (Republic Of Guinea And Senegal)

The high rainfall variability observed especially from the 1970s has intensified the vulnerability of water resources in tropical watersheds. It resulted in the recurrence of extreme hydrological events – combined with the increase in temperature which increases evapotranspiration causing considerable water losses – but also in the "Sahelization" of Sudanian areas resulting in the migration of isohyets towards the south.This article studies recent spatial and temporal changes in rainfall in the Kayanga-Anambé complex, as well as their potential hydrological implications. The methodological approach is based on (i) checking the quality of data and filling gaps using the method of rainfall indices with the Regional Vector Method (RVM); and on (ii) the analysis of spatial and temporal variability of rainfall using PETITT stationarity test and Standardized Precipitation Index (SPI).The evolution of rainfall in the basin is reflected in a fact specific to the intertropical zone, namely the variability of rainfall. This is marked by several sequences: a wet period between 1940 and 1967, followed by a long dry sequence which extends between the beginning of the 70s until the end of the 90s, and finally a slight resumption of the rainfall over the period 1993-2020. However, according to the outputs of global climate models ("Multi-model Ensemble"), the resumption of rainfall in the Kayanga basin will only be effective from 2060. This variability noted in the rains will induce a similar variability in the flows and agricultural production since they are largely dependent on it.

Revisiting the Relationship Between Tropical Cyclone Rapid Intensification and the Distribution of Inner‐Core Precipitation

AbstractThe relationship between tropical cyclone (TC) rapid intensification (RI) and the distribution of inner‐core precipitation preceding RI is reexamined using satellite‐based precipitation measurements and best‐track data. TCs experiencing RI (RITCs) are classified into weakly, moderately and highly asymmetric categories according to the 25th and 75th percentiles of an objective asymmetry index. Composite results indicate that weakly‐to‐moderately asymmetric RITCs experience precipitation axisymmetrization before RI, resulting from increased coverage of both light‐to‐moderate (0.5–10 mm hr−1) and intense rainfall (>10 mm hr−1) upshear. Contrarily, the rainfall asymmetry strengthens significantly before RI in highly asymmetric RITCs due to an outbreak of intense convection downshear left, demonstrating climatologically that RI is not necessarily preceded by rainfall axisymmetrization. It is hypothesized that the different rainfall evolution characteristics may be explained by the balanced intensification theory, and the azimuthal‐mean precipitation rate normalized by TC intensity could be a predictor for RI regardless of the rainfall asymmetry.

The Observed Effects of Cold Pools on Convection Triggering and Organization During DYNAMO/AMIE

AbstractCold pools that form from existing convection can generate new clouds nearby, a process that has been suggested to contribute to cloud organization. However, some disagreement exists on the role of cold pools in cloud organization over tropical oceans, and much remains to be understood on how this role depends on the state of large‐scale disturbances such as the Madden‐Julian Oscillation (MJO). This study addresses this question by examining the intraseasonal variability in the properties of cold pools and their effects on convection triggering using observations. The unique set of surface meteorology data and ground‐based radars deployed during the DYNAMO/AMIE field campaign are used to identify cold pools and the associated spatiotemporal evolution of rainfall. The results suggest that cold pools enhance rainfall at their expected speed of 3–8 m s−1, which includes the Doppler‐shifting effect by the background wind. The cold pools also enhance rainfall mainly within a 20 km radius, especially in the direction of boundary‐layer vertical wind shear. However, gravity waves appear to contribute predominantly to the propagation of convection over a wider range of distances due to their faster propagation speeds. The interface of convection triggering and propagation at different speeds of cold pools and gravity waves seems to contribute to cloud organization. The effectiveness of cold pools and gravity waves on cloud organization also depends highly on the MJO due to the combined effects of changes in environmental humidity and boundary to lower‐tropospheric wind.

Spatio-Temporal Evolution of Rainfall over the Period 1981–2020 and Management of Surface Water Resources in the Nakanbe–Wayen Watershed in Burkina Faso

Spatio-temporal analysis of rainfall trends in a watershed is an effective tool for sustainable water resources management, as it allows for an understanding of the impacts of these changes at the watershed scale. The objective of the present study is to analyze the impacts of climate change on the availability of surface water resources in the Nakanbe–Wayen watershed over the period from 1981 to 2020. The analysis was conducted on in situ rainfall data collected from 14 meteorological stations distributed throughout the watershed and completed with CHIRPS data. Ten precipitation indices, recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices), were calculated using the RClimDex package. The results show changes in the distribution of annual precipitation and an increasing trend in annual precipitation. At the same time, a trend towards an increase in the occurrence and intensity of extreme events was also observed over the last 4 decades. In light of these analyses, it should be emphasized that the increase in precipitation observed in the Nakanbe–Wayen watershed is induced by the increase in the occurrence and intensity of events, as a trend towards an increase in persistent drought periods (CDD) is observed. This indicates that the watershed is suffering from water scarcity. Water stress and water-related hazards have a major impact on communities and ecosystems. In these conditions of vulnerability, the development of risk-management strategies related to water resources is necessary, especially at the local scale. This should be formulated in light of observed and projected climate extremes in order to propose an appropriate and anticipated management strategy for climate risks related to water resources at the watershed scale.

Soil moisture–precipitation feedbacks in pre‐ and post‐monsoon landfalling tropical cyclones in Bay of Bengal

AbstractThe Bay of Bengal (BoB) experiences an average of three to four tropical cyclones (TCs) annually. The high population density of surrounding countries often leads to disastrous consequences when a TC makes landfall. As a result, it is critical to understand the evolution and intensity of rainfall associated with a TC that originates in the BoB. In this study, we examine the impact of initial soil moisture (SM) conditions on the TC track, TC recycled precipitation, and other TC variables using the Weather Research and Forecasting (WRF) model upgraded with Eulerian water‐tagging capabilities. We simulated pre‐monsoon TCs Amphan, Titli, Viyaru and post‐monsoon cyclones Phailin, Titli and Helen originating in the BoB. We conducted sensitivity experiments with dry and wet initial SM conditions to determine the impact of initial SM changes on TCs. We also generated four control simulations for each TC by changing the initial time to assess the effect of internal model variability. Our results indicate that initial SM conditions impact TC more than the internal model variability. We find that changes in the initial SM affect the latent heat flux, which influences the temperature and the synoptic wind pattern over the entire domain, resulting in changes in the TC properties. We find the feedback of SM to TC precipitation (quantified as recycled precipitation) is stronger as the TC approaches the landfall. The post‐landfall recycling ratio for pre‐monsoon TCs is approximately 5%–10%, but is around 20%–30% for post‐monsoon TCs. We observe that the Viyaru, Titli and Helen TC tracks are more sensitive to the initial SM conditions compared to the other three TCs. In addition to SM, we find that factors such as proximity to land, and TC intensity also have a role in determining the quantity of recycled precipitation for a TC.

Characteristics of the temporal and spatial evolution of rainfall under the influence of urbanization: a case study of the Beijing–Tianjin–Hebei region

Abstract With rapid urbanization in recent years, the frequency of extreme rainfall events has increased in major cities around the world during the flood season, and the social and economic losses caused by heavy rainfall are becoming increasingly serious. The results show that (1) the overall duration of rainfall exhibits a downward trend, and the overall spatial performance gradually decreases from east to west. (2) The mountainous areas are prone to light and moderate rainfall events; the plains are more prone to rainfall events at levels above moderate rain, especially rainstorms and heavy rain events; the probability of light and moderate rainfall events in the suburbs is close to that of the urban areas, but the probability of rainfall events at levels above heavy rain is less than that of the urban areas; the probability of rainfall events of all levels in the outer suburbs is higher. (3) Increase in rainfall in urban areas compared to the southern suburbs is greater. (4) With increasing urbanization, the built environment in the mountainous areas and plains has continued to grow, and the original underlying surface conditions have changed.

Statistical study and analysis of annual rainfall in the Naama region (Algeria)

Knowing the recent evolution and variability of the climate in arid and semi-arid regions is a necessity to anticipate what the consequences on the environments and societies of these regions could be, and thus define sustainable adaptation policies. In this modest work we studied the evolution of rainfall in an arid region. Thus, a good knowledge of the rainfall distribution both in time and in space, is essential to identify on the one hand the critical periods of drought to which the crops are exposed and on the other hand the favorable zones and the zones unfavorable. In this perspective, we have contributed to study the essential element of the balance which is the precipitations by using the statistical treatment and the analysis of the indices of dryness, also we adopted a methodology which is characterized by the Collection of the pluviometric data and creation from a computer database.
 The calculation of the indices for the different stations reveals the existence of two distinct wet and dry periods. Drought years are more notable as they can set in for 4 years. There is a decrease in rainfall during this study period but it is also interrupted by other years of high rainfall in certain regions such as El Kheiter and Mecheria. It is as if the further south you go, the more the drought impact is present.

Drought from the 1970s to the 1990s and its Influence in the Tropical City of Beni, Eastern DR Congo

Regional and local climate variability has serious consequences on water resources, ecosystems, and socio-economic activities. With the inexistence of rainfall stations, it is important to reconstruct the past climate with existing data and explore new possibilities for monitoring future climate evolution in the tropical city of Beni. The objective of this paper is to date the 1970-1990 drought and determine the rainfall trend in the tropical city of Beni. To this purpose, a 45-year rainfall time series (period 1974-2019) was analyzed using the Standardized Precipitation Index (SPI). The results of the paper indicate that the average annual rainfall ranges from 693 to 3080 mm with an average of 1827 ± 480.65 mm. The Hubert segmentation procedure applied to the rainfall series reveals three breaks (sub-periods): 1974-1979 (mean 1205.7 mm), 1980-2007 (mean 1736.68 mm), and 2008-2019 (mean 2348.01 mm). After the 2000s, the analysis shows an increasing trend in rainfall. A rainfall deficit of 35.20% is recorded during the period 1974-1979 compared to the period 1980-2007 and 22.61% for the period 1980-2007 compared to the period 2008-2019. The results of this study demonstrate that the city of Beni would have suffered from the drought of the years 1970-1990. Future research should focus on the future evolution of rainfall. However, understanding this future evolution requires long-term data, which is not the case for the tropical city of Beni. Therefore, there is a need for policymakers in collaboration with scientific actors to install meteorological stations to collect climate data.

Dynamic comparative analysis of different types of precipitation caused by landfalling strong typhoons over South China

Based on multiple datasets, a comparative analysis has investigated the different rainfall distributions and the factors related to strong (weak) rainfall induced by landfalling strong typhoons moving northwest (SR-NWLFSTYs, WR-NWLFSTYs) which are defined from the tracks, the locations, and intensities of the rainfall center of LFSTYs based on a dynamic composite analysis method.The obviously stronger rainfall induced by SR-NWLFSTYs, with the intensive rainfall center presenting a cyclonic rotation in the lifecycle of typhoons, tends to be accompanied by the pronouncedly enhanced low-level jet and a warmer SST before and during landfall. Owing to the enhanced low-level jet, moisture convergence experiences an intensification, resulting in a warmer and more humid circulation. Sufficient water vapor and latent heat is favorable for the enhancement of the mid-troposphere warm core structure with longer maintenance which can prolong the impact period of typhoons, leading to continuous precipitation. Simultaneously, the coupling of low-level convergence and upper-level divergence provides favorable dynamic conditions, thus further promoting the upward transportation of moisture through Ekman pumping, which tends to increase the mid-troposphere moisture through moisture advection. The changes in the mid-troposphere moisture coincide well with the evolution of rainfall over the same region during the lifecycle of typhoons.Comparatively, the asymmetric rainfall features of WR-NWLFSTYs with intense rainfall center mainly placed in the northeast quarter of the TC center during the lifecycle of TCs is likely related to the relatively weaker low-level jet which remains almost constant during and after landfall. The weaker low-level flow transports less moisture into the cyclone, and prohibits the weakening of vertical wind shear after landfall, leading to reduced precipitation with an obvious asymmetric distribution. Concurrently, the configuration of the weakening upper-level divergence and low-level convergence after landfall has been unable to maintain the upward motion for precipitation, resulting in relatively weaker rainfall for WR-NWLFSTYs.

Mutual Information Boosted Precipitation Nowcasting from Radar Images

Precipitation nowcasting has long been a challenging problem in meteorology. While recent studies have introduced deep neural networks into this area and achieved promising results, these models still struggle with the rapid evolution of rainfall and extremely imbalanced data distribution, resulting in poor forecasting performance for convective scenarios. In this article, we evaluate the amount of information in different precipitation nowcasting tasks of varying lengths using mutual information. We propose two strategies: the mutual information-based reweighting strategy (MIR) and a mutual information-based training strategy (time superimposing strategy (TSS)). MIR reinforces neural network models to improve the forecasting accuracy for convective scenarios while maintaining prediction performance for rainless scenarios and overall nowcasting image quality. The TSS strategy enhances the model’s forecasting performance by adopting a curriculum learning-like method. Although the proposed strategies are simple, the experimental results show that they are effective and can be applied to various state-of-the-art models.