Frequent Rain Research Articles

Effects of Explicit Convection on Future Projections of Mesoscale Circulations, Rainfall, and Rainfall Extremes over Eastern Africa

AbstractEastern Africa’s fast-growing population is vulnerable to changing rainfall and extremes. Using the first pan-African climate change simulations that explicitly model the rainfall-generating convection, we investigate both the climate change response of key mesoscale drivers of eastern African rainfall, such as sea and lake breezes, and the spatial heterogeneity of rainfall responses. The explicit model shows widespread increases at the end of the century in mean (~40%) and extreme (~50%) rain rates, whereas the sign of changes in rainfall frequency has large spatial heterogeneity (from −50% to over +90%). In comparison, an equivalent parameterized simulation has greater moisture convergence and total rainfall increase over the eastern Congo and less over eastern Africa. The parameterized model also does not capture 1) the large heterogeneity of changes in rain frequency; 2) the widespread and large increases in extreme rainfall, which result from increased rainfall per humidity change; and 3) the response of rainfall to the changing sea breeze, even though the sea-breeze change is captured. Consequently, previous rainfall projections are likely inadequate for informing many climate-sensitive decisions—for example, for infrastructure in coastal cities. We consider the physics revealed here and its implications to be relevant for many other vulnerable tropical regions, especially those with coastal convection.

Rainfall Characteristics in the Mantaro Basin over Tropical Andes from a Vertically Pointed Profile Rain Radar and In-Situ Field Campaign

Information on the vertical structure of rain, especially near the surface is important for accurate quantitative precipitation estimation from weather and space-borne radars. In the present study, the rainfall characteristics, from a vertically pointed profile Radar in the Mantaro basin (Huancayo, Peru) are observed. In summary, diurnal variation of near-surface rainfall and bright band height, average vertical profiles of the drop size distribution (DSD), rain rate, radar reflectivity (Ze) and liquid water content (LWC) are investigated to derive the rainfall characteristics. Diurnal variation of rain rate and bright band height show the bimodal distribution, where frequent and higher rain rate occurred during the afternoon and nighttime, and more than 70% bright band height found between 4.3–4.7 km. The average vertical profiles of Ze show the opposite characteristics above and below the melting level (ML) and depend on the near-surface rain rate. For example, the average Ze profiles have a negative gradient above the ML, whereas below, the ML, the gradient depends on the near-surface rain rate. The rain rate and LWC show the opposite behavior, and both consist of a positive (negative) gradient below (above) the ML. The vertical growth of DSD parameters depend on the near-surface rain rate, and a higher concentration of large-sized of droplets are observed for higher near surface rain rate, however, the dominant modes of droplets are <1 mm throughout the vertical column. However, the most significant variation in DSD growth is observed for near-surface rain rate ≥20 mm/h. These findings suggest using different retrieval techniques for near surface rain estimation than the rest of the vertical profile and high rain rate events. The improved understanding of the tropical Andes precipitation would be very important for assessing climate variability and to forecast the precipitation using the numerical models.

Hydrography and geomorphology of Antananarivo High City (Madagascar)

ABSTRACT The city of Antananarivo is located in the central highlands of Madagascar, and is the largest urban center of the island. Considering the frequent heavy cyclonic rains frequently affecting the area, its geomorphological context is particularly prone to geo-hydrological hazards, such as landslides and flash floods, as recently proved during the disastrous events of the winters of 2015 and 2018. Field data and high-resolution remote sensing data interpretation (DEMs and satellite orthophotos) were combined in order to produce detailed hydrographic and geomorphological maps. The aim was to understand the processes acting in the Analamanga hill area, with special regards to the effect of human activity in modeling the natural landforms and exacerbating the geo-hydrological hazards. The obtained maps will provide management-planning tools to be used as a first step towards a risk reduction strategy in the Antananarivo historical urban center.

Aerosol Impacts on Mesoscale Convective Systems Forming Under Different Vertical Wind Shear Conditions

AbstractFollowing our previous study of wind shear effect on mesoscale convective system (MCS) organization under a clean atmospheric condition using the Weather Research and Forecasting model coupled with spectral‐bin microphysics, we conduct sensitivity simulations by increasing cloud condensation nuclei concentration to investigate aerosol impacts on MCSs forming under different wind shear conditions. We find that increased aerosols induce stronger updrafts and downdrafts in all MCSs. The stronger updrafts and enlarged convective core area contribute to larger vertical mass fluxes and enhance precipitation. The enhanced updrafts and vertical mass fluxes indicate convective invigoration. Increased updraft speed below 8‐km altitude is attributed to enhanced condensational heating, except for the weak wind shear and strong low‐level shear cases in which the enhanced low‐level convergence is another contributing factor. Interestingly, above 8‐km altitude, we see reduced updraft speed by the increased aerosols due to reduced vertical pressure perturbation gradient force. The accumulated rainfall and mean rain rate are increased with a greater occurrence frequency of heavy rain. Larger rain rate is seen in both convective and stratiform regions. In general, we see a higher frequency of deep clouds in the polluted condition because of invigorated convection, and more stratiform/anvil clouds, but a lower frequency of shallow warm clouds, with a larger significance for more organized MCSs. The consistently invigorated MCSs by aerosols under various wind shear conditions revealed by this study have important implications to weather and climate in warm and humid regions that are influenced by pollution.

Analysis of Genesis Rain in Spring Transition in Makassar

Extreme weather in this case heavy rains is common in the city of Makassar, both of which resulted in a flood or no flood. This type of research is descriptive research that aims to describe the incidence of rain in the transition season in Makassar. The source of data used in obtaining data on research in Makassar is secondary data. His research methods such as analysis method is based on monthly rainfall data to determine the monthly rainfall pattern using the Log Pearson III distribution methods and daily rainfall data duration of 3 hours early to analyze the frequency of rain by using Gumbel distribution methods. Based on the results in a graph of monthly rainfall patterns in the city of Makassar in the year (1985-2014) for 30 years and chart the frequency of daily rainfall duration 3 hours late in the year (2005 to 2014) for 10 years in the transition season in the city of Makassar, we can conclude that monthly rainfall patterns in Makassar is a monsoonal pattern with the second-largest peak intensity of rainfall occurs in January and December and the smallest intensity of rainfall occurs in August.

Land Gradation Effect Analysis on Permeability and Ponding Time on Repeat Rain Frequency: Laboratory Study with Rainfall Simulator

Analysis of Effect of Land Gradation on Permeability and Ponding Time in Frequency of Repeated Rain (Laboratory Studies with Rainfall Simulator) guided by Darwis Panguriseng and Mahmuddin. That soil permeability is the ability of soil to pass water or air. Soil permeability is usually measured in terms of the speed of water flowing in a certain time specified in units of cm/hour. Ponding time (tp) is the time difference between when it rains and the time when water begins to pool above ground level. The purpose of this study was to determine the effect of soil grading on permeability and inundation time with repeated frequency of rainfall with the same intensity on mixed soil types. This research method is a type of laboratory experimental research, using a rainfall simulator. The soil used in this study is mixed soil types. Furthermore, artificial rain is given with an intensity of I15, each intensity is used five times the frequency of rain and the inundation time readings and inundation height are carried out in the Rainfall Simulator experiment tank and for the permeability test, observation is done with the constant head test. The results showed the value of the permeability coefficient is inversely proportional to the increase in rainfall intensity and frequency of rain. Inundation height and final inundation time are directly proportional to increasing rainfall intensity and rainfall frequency.

Rain Effect Frequency of Infiltration Rate and Infiltration Capacity in Common Soil: Laboratory Test with Rainfall Simulator

Analyzing the Influence of Rain Frequency Infiltration Rate and Infiltration Capacity in Common Soil Type (Laboratory Testing Study With Rainfall Simulator). Infiltration is the flow of water into the ground through the soil surface. This process is a very important part of the hydrological cycle and in the process of transferring rain into the flow of water in the soil before reaching the river. Infiltration (infiltration rate and capacity) is influenced by various variables, including soil type, slope inclination, density and type of vegetation, soil moisture content, and rainfall intensity. This study aims to determine the effect of rainfall frequency on the infiltration rate and infiltration capacity on common soil types. This research is a type of laboratory experimental research, using rainfall simulator tool. The soil used in this study is common soil type. Furthermore, artificial rain was provided with intensity I5, I15, and I25 and performed infiltration rate reading on the Drain Rainfall Simulator. The rate and capacity of infiltration in common soils increase proportionally to the increased intensity of rainfall, the higher the intensity of rainfall the higher the infiltration occurring at the same level of rain frequency. The rate and capacity of infiltration in common soils decrease proportionally to the increasing frequency of rain, the more the frequency of rain the smaller the infiltration occurring at the same level of rainfall intensity

Dilution Processes of Rainfall-Enhanced Acid Mine Drainage Discharges from Historic Underground Coal Mines, New Zealand

In much of the world, seasonal weather patterns cause a flush of dissolved contaminants from mined areas at the beginning of wet seasons. However, on parts of New Zealand’s west coast, the annual rainfall exceeds 6000 mm/year, with frequent rain days regardless of season; in these conditions, chemically rich flushes are short-lived and subsequently diluted. We studied two historic underground mine sites on the Denniston Plateau. Historic drainages from the Coalbrookdale workings into the Cascade Mine area discharge between ≈ 100 and ≈ 1000 L/s, depending on rainfall volume and frequency. The frequent rain on the plateau dilutes the Coalbrookdale discharge waters, increasing its pH and decreasing dissolved AMD constituents. During short-term high rainfall events, the increased flow causes a flush of stored AMD for less than 10 h, with decreased pH and increased dissolved concentrations of AMD constituents. In contrast, historic drainage at the Sullivan Mine showed little response to rainfall and there was virtually no changes in chemistry during or after high rainfall events. While negative downstream impacts occur at both sites, this study showed that quantification of the variability within a site’s flow regime is critical in understanding the impact of a mine site’s AMD in high rainfall areas.

Current Dynamics of Hydric Erosion in the Kingouari, Mfilou and Djoué Watersheds in the Southwestern Part of Brazzaville City (Congo)

The objective of this study is to quantify soil losses in the Kinsoundi 16A district, located in the Kingouari, Mfilou and Djoue watersheds. The aim is to highlight the current dynamic of water erosion in this southwestern part of Brazzaville's urban area and to evaluate the effectiveness of the control measures used. The methodological approach adopted was based on: (i) the measurement of the evolution of the soil surface, using profilometers placed on the 12 main roads in the district where 68 measurement points have been installed, (ii) the three-dimensional measurement (volume) of 22 ravines and gullies that incise the district, (iii) the measurement of slopes along arteries using a clinometer, (iv) the inventory of facilities used to control soil erosion, (v) interviews with populations to understand the history of the phenomenon and the control methods used. The soil losses by surface stripping, measured on 12 roads from 2007 to 2010, are 78.1 t/ha. A destruction of 4.7 ha of land, or 2% of the Kinsoundi 16A territory and 94,247 t/ha of land, was removed from these watersheds in 20 years by the 22 ravines. The aggressive nature of this dynamic is explained by the combination of the following natural and anthropogenic factors: frequent rains (≥ 15 days/month) very erosive with a Rusa index of 287 to 866 points, sandy soils with more than 90%, without cohesion and fragile, densification of the habitat on the ground (2 houses on average per plot of 400 m2), resulting in increased waterproofing of surfaces and responsible for the current erosive runoff, the absence of channels to canalize and control runoff, hence roads transformed into storm water collectors. The control measures used by the populations are inadequate and therefore not very effective (bags of soil that can be degraded in three months, used tires, solid waste dumped at the head of the ravines). Those financed by the State are expensive gabions but of limited effectiveness around the treated ravine. It is therefore imperative to treat the entire district as a risk watershed, by strengthening its vulnerable sectors and by building and developing a coherent system to control rainwater runoff. These curative measures must be underpinned by preventive actions that are more effective and less expensive.

Assessment of the rain and wind climate with focus on wind turbine blade leading edge erosion rate and expected lifetime in Danish Seas

Our motivation for investigating the rain and wind climate in the Danish Seas is recent news on leading edge erosion on wind turbine blades at several offshore wind farms. The costs related to turbine blade repair are high. In this study we investigate the rain and wind climate at five coastal and three inland weather stations in Denmark. The coastal stations have much higher frequency of heavy rain than inland stations, in high wind conditions. The hypothesis is that leading edge erosion mainly develops during these few extreme events. The leading edge erosion rates and expected lifetime are calculated assuming similar turbines to be in operation at the eight site. The results of two damage increment models show similar results for the coastal stations but differ for two out of three inland sites. The kinetic energy model shows four times high erosion rates at the coastal sites versus the two inland sites. The accumulated rain model shows site independent erosion. The expected life is on average 3 years of the two damage models. The erosion safe mode control, i.e. reduced wind turbine tip speed during extreme rain events, is presented with relative profit from 2.8 to 4.8%.

Determination of design layer of rainfall for design of treatment facilities of surface runoff

The article assesses the influence of the initial data and the duration of observations on the calculated value of the sediment layer, which determines the performance of treatment facilities of surface runoff. At design of these constructions drain volume from a settlement rain is found. The error introduced by the grouping of initial data depending on the accepted gradation of intervals is determined. The daily layer of precipitation from low-intensity frequent rains with a period of a single excess of the calculated intensity of 0.05-0.1 years was determined (for the conditions of Samara). Recommendations on the choice of initial data in the design are given.

Assessing coincidence probability for extreme precipitation events in the Jinsha River basin

Global analyses show that climate change has already increased the frequency and strength of extreme weather events. The observed and remote-sensed precipitation productions have been deeply studied considering the stationary and non-stationary characteristics of extreme series. However, as these studies largely addressed the evolution of precipitation extremes at a single station, the consistency risk of extremes at multiple stations within close days has been little researched. In this paper, a multivariate frequency analysis method is proposed to reveal the exceeding and coincidence probabilities of the most dependent extreme precipitation series. First, a generalized extreme distribution, which has proved better at describing the tail behavior of extreme series, is developed to simulate the marginal distribution of rainfall extremes. Then, a mixed von Mises distribution is introduced to fit the occurrence time interval of the extreme events. Taking advantage of its flexibility in choosing arbitrary marginals, a copula is constructed to implement a joint probability analysis of extreme precipitation events at multiple stations. The upper reaches of the Yangtze River, where frequent heavy rains are the main source of the regional floods, were selected as a typical research area. Five hundred twenty-eight copula models were finally constructed by arbitrarily choosing two precipitation extreme series among the total 33 meteorological stations. The results revealed the risk of extreme rainfall occurrence once in 2, 5, 10, 20, 50, or 100 years, within a time interval of 1–90 days. The research has great significance for understanding complicated extreme events and is helpful for the disaster emergency response and management.

Development of Nomogram for Debris Flow Forecasting Based on Critical Accumulated Rainfall in South Korea

Climate change causes extreme weather events worldwide such as increasing temperatures and changing rainfall patterns. With South Korea facing growing damage from the increased frequency of localized heavy rains. In particular, its steep slope lands, including mountainous areas, are vulnerable to damage from landslides and debris flows. In addition, localized short-term heavy rains that occur in urban areas with extremely high intensity tend to lead a sharp increase in damage from soil-related disasters and cause huge losses of life and property. Currently, South Korea forecasts landslides and debris flows using the standards for forecasting landslides and heavy rains. However, as the forecasting is conducted separately for rainfall intensity and accumulated rainfall, this lacks a technique that reflects both amount and intensity of rainfall in an episode of localized heavy rainfall. In this study, aims to develop such a technique by collecting past cases of debris flow occurrences and rainfall events that accompanied debris flows to calculate the rainfall triggering index (RTI) reflecting accumulated rainfall and rainfall intensity. In addition, the RTI is converted into the critical accumulated rainfall (Rc) to use rainfall information and provide real-time forecasting. The study classifies the standards for flow debris forecasting into three levels: ALERT (10–50%), WARNING (50–70%), and EMERGENCY (70% or higher), to provide a nomogram for 6 h, 12 h, and 24 h. As a result of applying this classification into the actual cases of Seoul, Chuncheon, and Cheongju, it is found that about 2–4 h of response time is secured from the point of the Emergency level to the occurrence of debris flows.

A Study on the Improvement of Flood Forecasting Techniques in Urban Areas by Considering Rainfall Intensity and Duration

Frequent localized torrential rains, excessive population density in urban areas, and increased impervious areas have led to massive flood damage that has been causing overloading of drainage systems (watersheds, reservoirs, drainage pump sites, etc.). Flood concerns are raised around the world in the events of rain. Flood forecasting, a typical nonstructural measure, was developed to help prevent repetitive flood damage. However, it is difficult to apply flood prediction techniques using training processes because training needs to be applied at every usage. Other techniques that use predicted rainfall data are also not appropriate for small watershed, such as single drainage area. Thus, in this paper, a flood prediction method is proposed by improving four criteria (50% water level, 70% water level, 100% water level, and first flooding of water pipes) in an attempt to reduce flooding in urban areas. The four criteria nodes are generated using a rainfall runoff simulation with synthetic rainfall at various durations. When applying real-time rainfall data, these nodes have the advantage of simple application. The improved flood nomograph made in this way is expected to help predict and prepare for rainstorms that can potentially cause flood damage.

Evaluation of Rainfall Forecasts with Heavy Rain Types in the High-Resolution Unified Model over South Korea

Abstract Heavy rainfall events account for most socioeconomic damages caused by natural disasters in South Korea. However, the microphysical understanding of heavy rain is still lacking, leading to uncertainties in quantitative rainfall prediction. This study is aimed at evaluating rainfall forecasts in the Local Data Assimilation and Prediction System (LDAPS), a high-resolution configuration of the Unified Model over the Korean Peninsula. The rainfall of LDAPS forecasts was evaluated with observations based on two types of heavy rain events classified from K-means clustering for the relationship between surface rainfall intensity and cloud-top height. LDAPS forecasts were characterized by more heavy rain cases with high cloud-top heights (cold-type heavy rain) in contrast to observations showing frequent moderate-intensity rain systems with relatively lower cloud-top heights (warm-type heavy rain) over South Korea. The observed cold-type and warm-type events accounted for 32.7% and 67.3% of total rainfall, whereas LDAPS forecasts accounted for 65.3% and 34.7%, respectively. This indicates severe overestimation and underestimation of total rainfall for the cold-type and warm-type forecast events, respectively. The overestimation of cold-type heavy rainfall was mainly due to its frequent occurrence, whereas the underestimation of warm-type heavy rainfall was affected by both its low occurrence and weak intensity. The rainfall forecast skill for the warm-type events was much lower than for the cold-type events, due to the lower rainfall intensity and smaller rain area of the warm-type. Therefore, cloud parameterizations for warm-type heavy rain should be improved to enhance rainfall forecasts over the Korean Peninsula.

Regression Analysis of Strong El-Nino and La-Nina Periode to Groundwater Availability in Palembang City

El-Nino results in reduced air mass in most parts of Indonesia and can cause drought. In the La-Nina phase some parts of Indonesia will get more water vapor resulting in increased frequency of rain. Increased rainfall has an impact on groundwater availability. Groundwater availability illustrates the condition of water in the soil which is useful in many sectors of life, especially in the agricultural sector. This study aims to see the relationship between the El Nino and La Nina phenomena strongly by using SOI indicators on groundwater availability in Palembang. In the Strong El-Nino phase in 1994 and 1997 the SOI index had a moderate correlation with groundwater availability of 32% and 39%. In 2015 the correlation of SOI to groundwater avability was 79% indicating a strong relationship. In 2008 and 2011 which was a strong La-Nina phase the SOI index correlation value for groundwater availability was 46% and 45%, respectively, which indicated a moderate correlation.

Surface-Atmosphere Coupling Scale, the Fate of Water, and Ecophysiological Function in a Brazilian Forest.

Tropical South America plays a central role in global climate. Bowen ratio teleconnects to circulation and precipitation processes far afield, and the global CO2 growth rate is strongly influenced by carbon cycle processes in South America. However, quantification of basin‐wide seasonality of flux partitioning between latent and sensible heat, the response to anomalies around climatic norms, and understanding of the processes and mechanisms that control the carbon cycle remains elusive. Here, we investigate simulated surface‐atmosphere interaction at a single site in Brazil, using models with different representations of precipitation and cloud processes, as well as differences in scale of coupling between the surface and atmosphere. We find that the model with parameterized clouds/precipitation has a tendency toward unrealistic perpetual light precipitation, while models with explicit treatment of clouds produce more intense and less frequent rain. Models that couple the surface to the atmosphere on the scale of kilometers, as opposed to tens or hundreds of kilometers, produce even more realistic distributions of rainfall. Rainfall intensity has direct consequences for the “fate of water,” or the pathway that a hydrometeor follows once it interacts with the surface. We find that the model with explicit treatment of cloud processes, coupled to the surface at small scales, is the most realistic when compared to observations. These results have implications for simulations of global climate, as the use of models with explicit (as opposed to parameterized) cloud representations becomes more widespread.

Twelve Years of Daily Weather Descriptions in North America in the Eighteenth Century (Mexico City, 1775–86)

AbstractThe weather diary of Felipe de Zúñiga y Ontiveros was recorded in Mexico City from 1775 to 1786. It is the earliest meteorological observational record of Mexico. The diary provides daily meteorological information for rain frequency, temperature, frost, hail, thunderstorms, and wind, with higher resolution than any other contemporary documentation or natural proxy from this region. The seasonal distributions of rainy days, temperature, hail, and thunderstorms correspond well with those from the Tacubaya Observatory in Mexico City (1886–2016). Two drought periods (1780/81 and 1785/86) and one wet period (1782/83) were identified. The drought spanning from 1785 to 1786 is known in the literature as “the hunger year” because it represented the most severe famine during the colonial period (1521–1821). This paper analyzes—for the first time—this event at a daily scale. Similar to the reported droughts of 1909/10 and 2010/11, 1785/86 was a very dry period. But the dry conditions of 1785 were followed by intense frosts that started in late August and continued through September and October. This combination led to the destruction of crops and subsequent famine. The duration of the frost does not have analogs during the instrumental period, probably because of the intense warming and land changes registered over the last years in the region.

Assessing the extent of citrus trees root apparatus under deficit irrigation via multi-method geo-electrical imaging

Tree rooting strategies are driven by external and internal factors such as climate conditions (rain frequency, wind direction), soil structure and crop type. In order to ensure water efficiency for irrigated crops, it is essential to know how each crop adapts its rooting strategy. We couple Mise-a-la-masse (MALM) with Electrical Resistivity Tomography (ERT) for investigating orange tree roots undergoing different irrigation strategies (Partial Root-zone Drying – or PRD - versus Full Irrigation). This is a totally novel approach giving an overall picture of roots structure and functioning in the subsoil. Our results show clear differences of rooting extent between different irrigation strategies, and identify privileged direction of root development due to distinct RWU patterns. These results are corroborated also by seasonal monitoring of evapotranspiration (ET) and soil water content (SWC), which exhibit very large differences in the soil water distribution in space and time for the trees undergoing different irrigation schedules.

The potential of sustainable urban drainage systems (SuDS) as an adaptive strategy to climate change in the Spanish Mediterranean

ABSTRACT Changes in weather pattern caused by climate change generate more frequent extreme rain events as well as droughts. Sustainable urban drainage systems (SuDS) are useful adaptations to this new reality. The paper surveys the use of these systems in other countries in relation to their use in Spain, particularly the Spanish Mediterranean region. There is a future for more detention of floodwaters as well as more use against drought of water which can be treated and reused.