Accumulated Rainfall Amount Research Articles

Characteristics of Water Vapor Transport during the “7·20” Extraordinary Heavy Rain Process in Zhengzhou City Simulated by the HYSPLIT Model

Water vapor transport is an important foundation and prerequisite for the occurrence of rainstorms. Consequently, the understanding of water vapor transport as well as the sources of water vapor during rainstorm processes should be considered as essential to study the formation mechanism of rainstorms. In this study, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is adopted for backward tracking of water vapor transport trajectories and sources during the “7·20” extraordinary heavy rain process in Zhengzhou City of China that occurred on 20 July 2021. On this basis, the trajectory clustering method is applied to quantitatively analyze the contributions of water vapor sources, aiming to provide a basis for exploring the maintenance mechanism of this extreme rainstorm event. The spatio-temporal characteristics of this rainstorm event show that there are 4 consecutive days with the precipitation reaching or exceeding the rainstorm level across the whole Zhengzhou City, with the daily rainfall amounts at eight national meteorological stations all breaking their respective historical extreme values. The regional-averaged rainfall amount in Zhengzhou City is 527.4 mm, while the maximum accumulated rainfall amount reaches 985.2 mm at Xinmi station and the maximum hourly rainfall amount at Zhengzhou national meteorological station reaches 201.9 mm h−1. The water vapor sources for this rainfall process, ranked in descending order of contribution, are the Western Pacific, inland areas of Northwest China and South China, and South China Sea. The water vapor at lower levels is mainly transported from the Western Pacific and the South China Sea, while those from the inland areas of Northwest China and South China provide a supply of water vapor at upper levels to a certain extent. The water vapor at 950 hPa is mainly sourced from the Western Pacific and South China Sea, accounting for 56% and 44%, respectively. The water vapor at 850 hPa mainly derives from the Western Pacific and the inland areas of South China, contributing 58% and 34% of the total, respectively. The water vapor at 700 hPa mainly comes from the inland areas of Northwest China and South China Sea. Specifically, the water vapor from inland Northwest China contributes 44% of the total, acting as the primary source. The water vapor at 500 hPa is mainly transported from the inland areas of South China and Northwest China, with that from the inland South China (56%) being more prominent. The water vapor at all levels is mainly transported to the rainstorm region through the eastern and southern regions of China from the source areas. Additionally, there are some differences in the water vapor trajectories at a 6 h interval.

Predicting flood stages in watersheds with different scales using hourly rainfall dataset: A high-volume rainfall features empowered machine learning approach

Accurate prediction of instantaneous high lake water levels and flood flows (flood stages) from micro-catchments to big river basins are critical for flood forecasting. Lake Carl Blackwell, a small-watershed reservoir in the south-central USA, served as a primary case study due to its rich historical dataset. Bearing knowledge that both current and previous rainfall contributes to the reservoirs' water body, a series of hourly rainfall features were created to maximize predicting power, which include total rainfall amounts in the current hour, the past 2 h, 3 h, …, 600 h in addition to previous-day lake levels. Notedly, the rainfall features are the accumulated rainfall amounts from present to previous hours rather than the rainfall amount in any specific hour. Random Forest Regression (RFR) was used to score the features' importance and predict the flood stages along with Neural Network – Multi-layer Perceptron Regression (NN-MLP), Support Vector Regression (SVR), Extreme Gradient Boosting (XGBoost), and the ordinary multi-variant linear regression (MLR) together with dimension reduced linear models of Principal Component Regression (PCR) and Partial Least Square Regression (PLSR). The prediction accuracy for the lake flood stages can be as high as 0.95 in R2, 0.11 ft. in mean absolute error (MAE), and 0.21 ft. in root mean square error (RMSE) for the testing dataset by the RFR (NN-MLP performed equally well), with small accuracy decreases by the other two non-linear algorithms of XGBoost and SVR. The linear regressions with dimension reductions had the lowest accuracy. Furthermore, our approach demonstrated high accuracy and broad applicability for surface runoff and streamflow predictions across three different-sized watersheds from micro-catchment to big river basins in the region, with increases of predicting power from earlier rainfall for larger watersheds and vice versa.

Real-time attribution of the influence of climate change on extreme weather events: a storyline case study of Hurricane Ian rainfall

As the Earth continues to warm due to human greenhouse gas emissions, there is a growing need to efficiently communicate the effect that global warming has on individual extreme weather events. Using a storyline approach, we present a rapid attribution of the increase in rainfall over Florida during Hurricane Ian in 2022 due to climate change as a case study. We find that extreme accumulated rainfall amounts associated with Hurricane Ian increased by 18%, far in excess of what would be expected by Clausius–Clapeyron scaling. The study offers a blueprint for rapid operational climate change attribution statements about extreme storms and other very rare weather events.

Event‐based precipitation characteristics related to cloud‐top temperature during pre‐summer rainy season over south China

AbstractPrecipitation exists in the form of event, which means all pixels within the same event have similar atmospheric condition and development experiences. Therefore, using GPM DPR and Himawari‐8 AHI data from 2016 to 2020, we carried out event‐based investigations on precipitations during the pre‐summer rainy season over south China. The identified rain clusters (RCs) were classified into three classes based on the mode of cloud‐top temperature, including those <230, 230–265, and >265 K. The results show that RCs with mode of cloud‐top temperature <230 K were related to low‐level velocity and jet. The atmospheric layer was very unstable with sufficient moisture supply, so the ratio of convective precipitation reached as high as 20% with largest droplet size. RCs at 230–265 K were mainly frontal stratiform precipitations caused by quasi‐stationary front. The atmospheric layer was stable but the horizontal moisture flux was strong; precipitations often appeared as continuous light rain with high droplet density and small droplet size. RCs with mode of cloud‐top temperature >265 K contributed less than 10% of the accumulated rainfall amount. They were mainly warm‐cloud shallow precipitations triggered by local convection with low droplet density. Our results suggest that the event‐scale characteristics of precipitation are indicative of the triggers and microphysics of precipitation.

Land cover changes the soil moisture response to rainfall on the Loess Plateau

AbstractInsight into the rainfall‐soil moisture (SM) response to land cover is critical for soil hydrological process modelling and management. In this study, five typical land‐cover types (forest, shrub, grass, crop and bare land) and four rainfall patterns (heavy, intermediate, light and continuous rains) were selected to assess the effects of SM response characteristics on the Loess Plateau of China. We monitored SM at five depths on each land‐cover type at 1‐h intervals over the growing season of 2019. The results showed that rainfall patterns and land‐cover types together determined the SM response process and infiltration efficiency. A minimum accumulated rainfall amount of 5 mm was the threshold required to trigger a 10‐cm SM response. Rain events with a higher intensity and smaller total rainfall amount triggered a quick surface SM response, while larger amounts could percolate deeper and faster. Land‐cover change significantly altered the rainfall‐SM response dynamics and rainwater utilization efficiency after 20 years of ecological construction. Revegetation sites (mean values of forest, shrub and grass) increased the soil wetting depth by 14.7%, shortened the SM response time by 27.3%, and accelerated the SM wetting front velocity by 67.2%, which promoted a 35.2% rainfall transformation rate (RTR) across the 1‐m profile over all rainfall events (R1–13). Moreover, planted forest showed the highest RTR of R1–13 and the maximal increase in soil water storage, which did not aggravate the soil water deficit across the 1‐m profile over the growing season. Therefore, we present evidence that planted forests, instead of shrubs, may be beneficial for water conservation if precipitation is greater than 550 mm. The findings of this study prove the role of revegetation on rainwater infiltration capacity and efficiency and can help improve the management of afforestation in arid and semiarid regions.

Comparison of summer raindrop size distribution characteristics in the western and central Tianshan Mountains of China

AbstractThe microphysical processes of cloud and precipitation in the Tianshan Mountains still remain unclear due to the complex terrain and the lack of ground‐based observational data. In this study, the characteristics of summer raindrop size distribution (RSD) in the western and central Tianshan Mountains of China were investigated in 2020 and 2021. According to the average raindrop spectra, the RSD characteristics exhibit significant differences that the concentration of medium and large particles is relatively higher at Zhaosu than that at Tianchi. Weak precipitation prevails in the Tianshan Mountains most of the time, yet moderate rainfall and heavy rainfall have a great impact on the accumulated rainfall amount. For each rainfall rate class, raindrops of diameter less than 0.75mm have a lower concentration and raindrops of diameter greater than 3 mm have a higher concentration at Zhaosu as compared to those at Tianchi. Compared with Tianchi, Zhaosu has a larger mass‐weighted mean diameter (Dm) and a lower normalized intercept parameter (log10Nw). Compared with the classical convective spectrum, the RSDs at both Zhaosu and Tianchi are similar to the continental convective cluster. The relationships between the shape and slope (μ–Λ), and radar reflectivity and rainfall rate (Z–R) exhibit a significant difference in the western and central Tianshan Mountains of China.

Attribution of 2020 hurricane season extreme rainfall to human-induced climate change

The 2020 North Atlantic hurricane season was one of the most active on record, causing heavy rains, strong storm surges, and high winds. Human activities continue to increase the amount of greenhouse gases in the atmosphere, resulting in an increase of more than 1 °C in the global average surface temperature in 2020 compared to 1850. This increase in temperature led to increases in sea surface temperature in the North Atlantic basin of 0.4–0.9 °C during the 2020 hurricane season. Here we show that human-induced climate change increased the extreme 3-hourly storm rainfall rates and extreme 3-day accumulated rainfall amounts during the full 2020 hurricane season for observed storms that are at least tropical storm strength (>18 m/s) by 10 and 5%, respectively. When focusing on hurricane strength storms (>33 m/s), extreme 3-hourly rainfall rates and extreme 3-day accumulated rainfall amounts increase by 11 and 8%, respectively.

Increased Occurrence and Intensity of Consecutive Rainfall Events in the China's Three Gorges Reservoir Area Under Global Warming

AbstractConsecutive rainfall events (CREs) are important triggers of geological hazards like landslide downhill and mudslide in the Three Gorges Reservoir area (TGR), China. These hazards are not only potential risks for the effective storage capacity of the reservoir but also threats of the safety of the reservoir's Great Dam. The future changes of CREs' occurrence and intensity are analyzed by using the projection experiments from 20 models attending the Coupled Model Intercomparison Project Phase 5 (CMIP5) under three different representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5). Spring and fall are focused on, during which CREs are most frequent. Considering a common overestimate of rainy days number in the state‐of‐the‐art models, a new approach is developed to define CREs based on the percentile of rainfall distribution in observations. The approach yields a similar CREs climatology in models to that in observations and thus is used to identify CREs in models. The results based on multiple model ensemble (MME) and model spread comparison suggest a significant increase in spring and an overall decrease in fall in CREs' occurrence under all three scenarios. As for the intensity, it is projected to intensify in both spring and fall. Particularly, the higher the emission scenario, the greater the spring accumulated rainfall amount during a single CRE. These results imply an increasing risk of geological hazards in the TGR in the future.

Acquiring unbiased rainfall duration and intensity data from tipping-bucket rain gauges: A new approach using synchronised acoustic recordings

Tipping-bucket rain gauges (TBRGs) are an established and proven means of recording rainfall amount, but are not well-suited to the estimation of rainfall duration, owing to lag times arising from bucket filling. TBRG data are unable to reveal aspects of rainfall arrival such as short-term rainfall intermittency; nor can they adequately capture the start and end times of low intensity rain. These limitations pose challenges for the estimation of rainfall rates, for which accurate rain duration must be known. Here, a new approach to this problem is explored: the use of acoustic recording apparatus co-located with a TBRG for the principal purpose of identifying true raining time. From an Australian wet tropical ground observing station, TBRG data were processed to yield 5 min, 15 min, and 1 h accumulated rainfall amounts, and corresponding estimates of raining time. These were compared with raining time estimated from high-precision WAV recordings of raindrop arrival sensed by a responsive drum skin. The acoustic recording allowed true raining time to be measured, and compared with the TBRG data. Only rarely did the TBRG rain durations provide acceptable accuracy; generally, they were severely biased. Moreover, the 5 min data consistently provided estimates with larger bias than did 15 min or 1 h data. In general, none of the TBRG rainfall data provided acceptable estimates of rain duration, and hence derived intensity data were also badly biased. These findings have clear implications for the widespread use of time-aggregated TBRG data, such as hourly rainfall amounts. These may yield little or no accurate information on rainfall intensities; the marked bias of rain duration estimated from TBRG data may hamper attempts to detect and quantify secular change in rainfall frequency, duration, and intensity. Acoustic methods provide an economical means to provide less biased data.

Influence of canopy and topographic position on soil moisture response to rainfall in a hilly catchment of Three Gorges Reservoir Area, China

Rainfall provides essential water resource for vegetation growth and acts as driving force for hydrologic process, bedrock weathering and nutrient cycle in the steep hilly catchment. But the effects of rainfall features, vegetation types, topography, and also their interactions on soil water movement and soil moisture dynamics are inadequately quantified. During the coupled wet and dry periods of the year 2018 to 2019, time-series soil moisture was monitored with 5-min interval resolution in a hilly catchment of the Three Gorges Reservoir Area in China. Three hillslopes covered with evergreen forest (EG), secondary deciduous forest mixed with shrubs (SDFS) and deforested pasture (DP) were selected, and two monitoring sites with five detected depths were established at upslope and downslope position, respectively. Several parameters expressing soil moisture response to rainfall event were evaluated, including wetting depth, cumulative rainfall amount and lag time before initial response, maximum increase of soil water storage, and transform ratio of rainwater to soil water. The results indicated that rainfall amount is the dominant rainfall variable controlling soil moisture response to rainfall event. No soil moisture response occurred when rainfall amounts was 30 mm. In the wet period, the cumulative rainfall amount to trigger surface soil moisture response in EG-up site was significantly higher than in other five sites. However, no significant difference in cumulative rainfall amount to trigger soil moisture response was observed among all study sites in dry period. Vegetation canopy interception reduced the transform ratio of rainwater to soil water, with a higher reduction in vegetation growth period than in other period. Also, interception of vegetation canopy resulted in a larger accumulated rainfall amount and a longer lag time for initiating soil moisture response to rainfall. Generally, average cumulative rainfall amount for initiating soil moisture response during dry period of all sites (3.5–5.6 mm) were less than during wet period (5.7–19.7 mm). Forests captured more infiltration water compared with deforested pasture, showing the larger increments of both soil water storage for the whole soil profile and volumetric soil water content at 10 cm depth on two forest slopes. Topography dominated soil subsurface flow, proven by the evidences that less rainfall amount and less time was needed to trigger soil moisture response and also larger accumulated soil water storage increment in downslope site than in corresponding upslope site during heavy rainfall events.

Analysis of urban rainfall from hourly to seasonal scales using high‐resolution radar observations in the Netherlands

AbstractIn this article an analysis of urban rainfall from hourly to seasonal scales is conducted for the Netherlands, with a focus on its capital, Amsterdam. In addition, the potential of synoptic weather types and local wind directions to categorize extreme rainfall in Amsterdam is assessed. An analysis of gauge‐adjusted daily radar rainfall retrievals with 1 km spatial resolution for 10 years shows that rainfall is enhanced over Dutch cities compared to their rural surroundings, with a maximum of a 14.2% increase over the largest cities in winter. The annual cumulative rainfall in Amsterdam appears to be significantly higher compared to its surroundings. This is due both to the higher frequency of occurrence of urban rainfall and to the higher hourly mean intensities. Extreme hourly rainfall rates appear to be affected by urban areas only in summer. Diurnal and weekly rainfall cycles do not reveal any significant urban influence. A wind direction analysis reveals that extreme rainfall events can primarily be attributed to westerly and next to southerly air masses. An analysis of the Jenkinson and Collinson (JC) and the German Weather Service (Deutscher Wetterdienst, DWD) weather types with rainfall and extreme rainfall events reveals that the JC weather types are more indicative of situations associated with rainfall extremes, whereas the DWD weather types are more indicative of situations resulting in higher accumulated rainfall amounts.

Effects of Anthropogenic Aerosols on a Heavy Rainstorm in Beijing

A heavy rainstorm occurred in Beijing on 19–20 July 2016. The Weather Research and Forecasting Model coupled with Chemistry (WRF-Chem) was used to investigate the effects of anthropogenic aerosols on precipitation and microphysical processes. Three conditions were simulated by altering the anthropogenic emissions. When the anthropogenic emissions were increased by 10 times, the area-average accumulated rainfall amount and maximum accumulated rainfall amount both decreased. The cloud water mixing ratio increased and the rain mixing ratio decreased. The radii of cloud droplets decreased, and the collision efficiency of cloud water by rain and the autoconversion rate of cloud water into rain were both low. When the anthropogenic emission was 10% of the original emission, the area of accumulated rainfall amounts greater than 25 mm in the Beijing area was 10% larger than those of the other two tests. The collision efficiency and autoconversion rate of cloud water into rain were high for large contact areas and large cloud droplets. The graupel mixing ratio was the largest. Thus, the process of melting of graupel into rain was the largest. In the WRF-Chem model, the aerosols did not participate as ice nuclei (IN) in the ice-phase microphysical processes, and therefore the aerosols could influence only the warm rain processes and mix-phased processes near the freezing level line. For no influence on ice-phase microphysical processes, the snow and ice mixing ratios did not show many differences among the different tests.

Effects of Cloud Microphysical Latent Heat on a Heavy Rainstorm in Beijing

The latent heat produced by cloud microphysical processes can greatly affect the thermal and dynamic structure of the atmosphere, as well as the development and evolution of clouds and precipitation. In this study, to examine the consequences of different kinds of latent heat produced by microphysical processes, four sensitivity tests were conducted based on the control simulation results of a heavy rainstorm occurred in Beijing on 21 July 2012 using the Weather Research and Forecasting Model (WRF). Without the latent heat absorption of evaporation, the convective cloud system developed stronger, and the accumulated precipitation amount increased. Without the latent heat release of deposition, the transit time of the surface front was delayed; in addition, the convective cloud system developed weakly. The accumulated conversion amounts of microphysical processes and the accumulated rainfall amount in the deposition adiabatic test were far less than those in the other tests. Without the latent heat of melting and freezing, the convective cloud system did not change substantially, and there was only a minor effect on precipitation. Hydrometeor production exhibited some changes related to precipitation in the five tests. The latent heat produced by the convective system varied substantially in the five tests with a change in the latent heat budget.

Weak Plane Failure of Phyllitic Sandstone: Back Analysis for Slope Stabilization and the Use of Probabilistic Approach for Design Optimization

The main access road of Mae Mao dam hydropower project, Chiang Mai province, Thailand, has failed during a sunny day. The question has been raised of what might have triggered the failure. At the day of failure, the precipitation amount was very small and the accumulated rainfall amount in the past days was also not significant to trigger the failure. Detail geotechnical investigations were carried out including the geological survey, seismic refraction survey, bore holes drilling and various laboratory testing. The rock found at site was Phyllitic and Quartzitic sandstone. It appears that the engineering properties of Phyllitic sandstone are more susceptible for slope failure. Rock and soil slope stability analysis have been done, however none of them was found to be the cause of failure. After carefully reexamining the geologic structure, it was found that there is a weak plane layer that resulted in the failure. A suitable stabilization method has been selected as the economical remedy of the slope failure. In this case, flattening the back slope is the economic method along with the drainage system specially designed to reduce the pore water pressure of the weak plane layer. Rock bolts and rock anchors were found to be uneconomical and unsuitable. Probabilistic approach was used to optimize the engineering safety and construction cost.

Comparison of Raindrop Size Distribution Characteristics Across the Southeast Asia Region

Satellite communication requires reliable estimates of the channel characteristics, especially with the future use of higher frequencies. Regardless of the rain rate, the shape of rain drop size distribution (DSD) start to considerably effect the specific attenuation. In this study DSDs are studied using ground-based two-dimensional video disdrometer measurements taken from Johor, Malaysia as well as two similar datasets from Gan and Manus, two equatorial islands. Integral rain parameters are studied to explain DSD variations across the Southeast Asia region. Slightly higher raindrop concentrations and larger diameters were observed in Johor than in Gan or Manus, which is due to Johor being affected by not only oceanic rain- fall but land rainfall as well. The measured rainfall was classified into convective and stratiform precipitation types; the results showed that the Southeast Asia region is dominated by convective rain in terms of accumulated rainfall amount, but stratiform rain occurred more frequently. Further, seasonal variations observed in Johor were insignificant and the DSD variation was mostly due to changes in percentage occurrence of the precipitation types for each monsoon season.

Soil moisture response to rainfall on the Chinese Loess Plateau after a long‐term vegetation rehabilitation

AbstractThe Chinese Loess Plateau (CLP) is a unique Critical Zone with deep loess deposits, where soil moisture is primarily replenished by seasonal monsoon rainfall. However, the role of vegetation, coupled with complex topography, on rainwater infiltration on the CLP, especially after long‐term revegetation for controlling erosion, is inadequately quantified. Over the growing season of 2016, we monitored soil moisture at the 30‐min interval at 5 depths (10, 20, 40, 60, and 100 cm) in an afforested catchment and a nearby catchment with natural regrowth of grasses. Two monitoring sites were established in each catchment, one in the downhill gully and the other in the uphill slope. We found that vegetation, topography, and rainfall attributes together determined rainwater infiltration and soil moisture replenishment. An accumulated rainfall amount of 9 mm was required to trigger soil moisture response at 10‐cm depth at the 2 grassland sites and the forestland uphill‐slope site whereas 14 mm of rainfall was required for the forestland gully site covered by dense undergrowth and trees. Rainfall events with larger sums and higher peak intensities permitted rainwater infiltration to deeper soil depths. However, no rain recharged soil moisture to 100‐cm depth during the monitoring period. The forestland uphill‐slope site showed the deepest wetting depth (up to 60‐cm depth), fastest wetting‐front velocity (up to 4 cm/hr below 10‐cm depth), and the most significant soil moisture increase (up to 15% cm 3 cm−3 increase at 10‐cm depth) after rainfall in the growing season. The grassland gully site had the highest soil water storage, whereas soil moisture was depleted the most at the forestland gully site. Findings of this study reveal the transient dynamics of soil moisture after rainfall on the CLP, which signifies the role of revegetation on rainwater infiltration in the loess Critical Zone.

Meteorological analysis of flash floods in Artvin (NE Turkey) on 24 August 2015

Abstract. On 24 August 2015 intense rainfall episodes generated flash floods and landslides on the eastern Black Sea coast of Turkey. As a consequence of the heavy rainstorm activity over Artvin and its surroundings (NE Turkey), 11 people died and economic losses totaled a million dollars. Over the 6 h of the event (from 05:00 to 11:00 UTC), total accumulated rainfall amounts of 136, 64, and 109 mm were measured in the Hopa, Arhavi, and Borçka settlements of Artvin city, respectively. This study comprehensively investigates the meteorological characteristics of those flash floods. In terms of synoptic mechanisms, the cutoff surface low from the summer Asian monsoon settled over the eastern Black Sea. After two days of quasistationary conditions of this cyclone, sea surface temperatures (SSTs) reached 27.5 °C (1.5 °C higher than normal) and low-level moisture convergence developed. In addition, transfer of moisture by warm northerly flows from the Black Sea and relatively cool southerly flows from the land coasts of the Artvin district exacerbated the unstable conditions and thus played a significant role in the development of deep convective cells. Severe rainstorms as well as the slope instability of the region triggered landslides and worsened flood damages in the Artvin area. This study supports conventional weather analysis, satellite images, and forecast model output to alert forecasters to the potential for heavy rainfall.

A statistical analysis of hourly heavy rainfall events over the Beijing metropolitan region during the warm seasons of 2007–2014

ABSTRACTA statistical analysis of the spatiotemporal characteristics of hourly heavy rainfall (HHR) events and rainstorm days, defined as greater than 20 mm h−1 and 50 mm day−1, respectively, is performed using observations at 5‐min intervals from 155 automated weather stations (AWSs) over the Beijing metropolitan region (BMR) during the warm seasons of 2007–2014. Results show pronounced variability in the frequencies and rainfall amounts of both HHR events and rainstorm days across the BMR of less than 150 km width from the west to east. That is, higher‐ (lower) frequency HHR events with more (less) accumulated rainfall amounts take place in eastern Haidian and over the BMR's northeast mountains (west and northwest mountains). Many extreme rainfall and even record‐breaking events, in terms of the frequency, duration, rainfall amount and intensity, are found to occur in the regions of high‐frequency HHR events and rainstorm days. The frequency of rainstorm days with HHR events accounts for more than 50% of that of total rainstorm days over the BMR's plains and near the northeast mountains. Results also show that HHR events occur most frequently in late July, and typically peak during 1600–2000 LST. A comparison of the averaged surface meteorological variables and upper‐air sounding at 0800 LST between HHR and non‐HHR days reveals that the occurrences of the HHR events coincide with the distribution of surface warmer and more humid air as well as organized convergence in the presence of an unstable environment with surface south‐ to southeasterly winds, low‐level south to southwesterly flows and a deep layer of higher moisture content. These results suggest likely the positive influences of urban environment and mountain‐plain circulations on the generation of the HHR events, given favourable larger‐scale conditions.

Daily precipitation estimation through different microwave sensors: Verification study over Italy

The accurate estimation of rainfall from remote sensing is of paramount importance for many applications as, for instance, the mitigation of natural hazards like floods, droughts, and landslides. Traditionally, microwave observations in the frequency between 10 and 183GHz are used for estimating rainfall based on the direct interaction of radiation with the hydrometeors within precipitating clouds in a so-called top-down approach. Recently, a bottom-up approach was proposed that uses satellite soil moisture products derived from microwave observations (<10GHz) for the estimation of accumulated rainfall amounts. The integration of the bottom-up and top-down approaches has large potential for providing high accurate rainfall estimates exploiting their different and complementary nature.In this study, we perform a long-term (3years) assessment of different satellite rainfall products exploiting the full range of microwave frequencies over Italy. Specifically, the integration of two top-down algorithms (CDRD, Cloud Dynamics and Radiation Database, and PNPR, Passive microwave Neural network Precipitation Retrieval) for estimating rainfall from conically and cross-track scanning radiometers, and one bottom-up algorithm (SM2RAIN) applied to the Advanced SCATterometer soil moisture product is carried out. The performances of the products, individually and merged together, are assessed at daily time scale. The integration of top-down and bottom-up approaches provides the highest performance both in terms of continuous and categorical scores (i.e., median correlation coefficient and root mean square error values equal to 0.71 and 6.62mm, respectively). In such a combination, the limitations of the two approaches are compensated allowing a better estimation of ground accumulated rainfall through SM2RAIN while, overcoming the limitations of rainfall estimation for intense events during wet conditions through CDRD-PNPR product. The accuracy and the reliability of the merged product open new possibilities for their testing in hydrological applications, such as the monitoring and prediction of floods and droughts over large areas, including regions where ground-based measurements are sparse or not available.

On the seasonal variation of various types of precipitation over global tropical ocean region: A perspective from TRMM measurements

The radar reflectivity and precipitation rate from Precipitation Radar (PR) onboard Tropical Rainfall Measuring Mission (TRMM) are obtained over the global tropical regions (35°S–35°N) during the period from 2007 to 2012, combined with coincident vertical velocity at 400 hPa ( ω 400 hPa), relative humidity at 850 hPa (RH850 hPa) and lower tropospheric stability (LTS) from European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis. First of all, the seasonal and spatial distribution of meteorological factors, including ω 400hPa, RH850 hPa, and LTS, together with rain rate are investigated. Next, four typical Regions of Interest (ROIs) and their individual seasons (i.e., favorable and non-favorable seasons for rainfall) are identified for further analysis by determining whether there exist most pronounced seasonal differences observed in ω 400 hPa. Meanwhile, rainy area, and rainfall of three precipitation types (i.e., shallow, stratus, and convection precipitation regimes) over the ROIs has been calculated. The three dimensional structures of individual precipitating system are analyzed, based on normalized contoured frequency by altitude diagram (NCFAD) and other statistical methods. Finally, with a focus on convection precipitation system, we give a quantitative description of the response of precipitation vertical structure to meteorological factors. Namely, how the rain echo top height (RTH), echo top height with reflectivity of 30 dBZ (ZTH30 dBZ), and reflectivity center of gravity (ZCOG) vary with ω 400 hPa, RH850 hPa, and LTS. In particular, (1) high rain rate dominates over intertropical convergence zone, which is characterized by strong updraft, sufficient moisture, and low LTS, showing the average rain rate is negatively associated with ω 400 hPa at both temporal and spatial scales. That is to say, lower ω 400hPa comes with more intensive rain rate. (2) The meteorological factors, along with average rain rate, exhibit appreciable seasonal variation. To be specific, negative (positive) ω 400 hPa anomalies is mostly found over the northern (southern) hemisphere in summer and autumn, as opposed to the patterns found in winter and spring. (3) In terms of the area with rainfall, the stratiform precipitating system accounts for more than 50% of the total area under investigation, followed by the convective precipitating system (about 30%), and the shallow precipitating system (less than 20%). In contrast, convective precipitating system, among others, takes the lead (about 65%) in contributing to the accumulated rainfall amount in the ROIs studied, followed by stratiform precipitating system (about 25%), and the shallow precipitating system (about 10%). (4) In the season with relatively higher ω 400 hPa, both rainy area and accumulated rainfall amount for all three types of precipitation show a increasing trend, irrespective of ROI. By comparison, rain rate and its vertical structures show large discrepancy, i.e., the intensity of convective precipitation system in favorable season tends to systematically increase as compared with that in non-favorable season. (5) The bulk precipitation system parameters used to describe convective precipitating system, including RTH, ZTH30 dBZ, and ZCOG, are observed to be elevated sharply with increasing ω 400 hPa and RH850 hPa. The same holds for the increasing LTS but with a smaller magnitude in the elevated height. This implies that ω 400 hPa and RH850 hPa most likely play a dominant role in dictating the vertical development of convection.