The impact of raindrops on Salvinia molesta leaves: effects of trichomes and elasticity

The floating leaves of the aquatic fern Salvinia molesta are covered by superhydrophobic hairs (=trichomes) which are shaped like egg-beaters. These trichomes cause high water repellency and stable unwettability if the leaf is immersed. Whereas S. molesta hairs are technically interesting, there remains also the question concerning their biological relevance. S. molesta has its origin in Brazil within a region exposed to intense rainfall which easily penetrates the trichome cover. In this study, drop impact on leaves of S. molesta were analysed using a high-speed camera. The largest portion of the kinetic energy of a rain drop is absorbed by elastic responses of the trichomes and the leaf. Although rain water is mostly repelled, it turned out that the trichomes hamper swift shedding of rain water and some residual water can remain below the ‘egg-beaters’. Drops rolling over the trichomes can, however, ‘suck up’ water trapped beneath the egg-beaters because the energetic state of a drop on top of the trichomes is—on account of the superhydrophobicity of the hairs—much more favourable. The trichomes may therefore be beneficial during intense rainfall, because they absorb some kinetic energy and keep the leaf base mostly free from water.

Evolution of Warm Season Intense Rainfall in Yaan Against a Cold-Anomaly Background

This study investigates the rainfall characteristics during intense rainfall over Yaan against a cold-anomaly background, aiming to refine the understanding of different kinds of rainfall events across complex terrain. Hourly rain gauge records, ERA5 reanalysis data and the black body temperature of cloud tops derived from FY-2E were used. The results show that against a cold-anomaly background, the regional rainfall events (RREs) in Yaan exhibit west-to-east propagation, which is different from the north-to-south evolution of warm RREs. The middle and upper troposphere is dominated by a negative geopotential height anomaly corresponding to the cold anomaly. The cyclonic circulation at the higher level associated with the negative geopotential height anomaly bends the high-level jet to the south, forming a divergent zone over the Tibetan Plateau (TP) and guiding mid-level systems to move eastward. The cyclonic circulation at the mid-level produces a wind shear zone over the TP, generating anomalous vorticity that continuously moves eastward and develops to influence the rainfall over Yaan. The cold Yaan RREs are closely related to the TP low-pressure systems (both vortex and shearline). The anomalous vorticity over the TP can influence the local vortex over the eastern periphery of the TP at a distance mainly by the horizontal advection of anomalous vorticity by the mean flow and then enhance the local vortex mainly by anomalous convergence when it moves near Yaan.

Value addition in district level dynamical forecast during intense rainfall spells over the west coast of India

lkj & ekulwu _rq ds nkSjku Hkkjr ds if’peh rV ij Hkkjh o"kkZ dh ?kVukvksa dk vjc lkxj ds Åij iouksa dh vf/kdre xfr ds ØksM ¼dksj½ ds lkFk ?kfu"B laca/k gSA bl 'kks/k&i= esa bZ- lh- ,e- MCY;w- ,Q- ¼;wjksih; e/;e vof/k iwokZuqeku dsUnz½ }kjk 850 gSDVkikLdy ij iwokZuqekfur 72 ?kaVs ds izokg izfr:i dk mi;ksx fd;k x;k gS ftlls if’peh rV ij Hkkjh o"kkZ dk iwokZuqeku djus ds fy, ftyk Lrjh; xfrdh; iwokZuqeku iz.kkyh dh {kerk c<+kus gsrq ek=kRed i)fr dk fodkl fd;k tk ldsA ;g ns[kk x;k gS fd if’peh rV ij o"kkZ dh ek=k dk if’peh rV ij vjc lkxj esa iou dh vf/kdre xfr ds 72 ?kaVs ds bZ- lh- ,e- MCY;w- ,Q- }kjk fd, x, iwokZuqeku ds lkFk egRoiq.kZ lglaca/k gSA if’peh rV ij Hkkjh o"kkZ ds {ks= ds v{kka’kh; foLrkj dk if’peh rV ij iou dh vf/kdre xfr ds ØksM ¼dksj½ ds lkFk egRoiw.kZ lglaca/k gSA bl 'kks/k&i= esa ;g crk;k x;k gS fd xzh"edkyhu ekulwu _rq ds nkSjku Hkkjr ds if’peh rV ij Hkkjh o"kkZ ds 72 ?kaVs dk iwokZuqeku djus ds fy, iouksa dh vf/kdre xfr ds 72 ?kaVs ds iwokZuqekfur ØksM ¼dksj½ vkSj foLrkj dh rhozrk vkSj fLFkfr dh {kerk c<+kus ds fy, laHkkfor iwoZlwpdksa ds :i esa mi;ksx fd;k tk ldrk gSA Occurrences of intense rainfall events over west coast of India during monsoon are intimately linked to the core of maximum winds over the Arabian Sea. ECMWF (Europian Centre for Medium Range Weather Forecasting ) predicted 72 hr flow pattern at 850 hPa has been used to develop a quantitative method for value addition in the district level dynamical forecast system for intense rainfall over the west coast. It has been found that the amount of rainfall over the west coast is significantly correlated to 72 hr ECMWF forecast of maximum wind speed over the Arabian Sea along the west coast. The latitudinal width of the heavy rainfall belt over the west coast has got significant correlation with the location of maximum wind core along the west coast. It has been shown that the strength and location of the 72 hr predicted core and fetch of maximum winds could be used as potential predictors in the value addition for 72 hr heavy rainfall forecast along the west coast of India during summer monsoon.

Raindrop Size Distribution and Rain Characteristics of the 2017 Great Hunan Flood Observed with a Parsivel2 Disdrometer

Disdrometer observations obtained by an OTT Parsivel2 during the 2017 Great Hunan Flood from 1:00 a.m. LST 23 June 2017 to 4:00 a.m. LST 2 July 2017 in Changsha, Hunan Province, southern China, are analyzed to diagnose characteristics of raindrop size distribution (DSD). This event was characterized by a large number of small- to medium-sized raindrops (diameters smaller than 1.5 mm) and the mean median volume diameter (D0) is about 1.04 mm. The median values of rain rate R (1.57 mm h−1), liquid water content W (0.10 g m−3), and radar reflectivity Z (25.7 dBZ) are smaller than that of the 2013 Great Colorado Flood. This event was composed of two intense rainfall periods and a stratiform period, and notable distinctions of rainfall microphysics among the three rainfall episodes are observed. Two intense rainfall periods were characterized by widespread and intense convection rains with a surface reflectivity of 48.8~56.7 dBZ. A maximum diameter of raindrops up to 7.5 mm was observed, as well as high concentrations of small and midsize drops, resulting in large rainfall amounts during the two intense rainfall episodes. The mean radar reflectivity of 22.6 dBZ, total rainfall of 17.85 mm and the maximum raindrop of approximately 4.25 mm were observed during the stratiform rainfall episode. The composite DSD for each rainfall episode peaked at 0.56 mm but higher concentrations of raindrops appeared in the two intense rainfall episodes. The Z-R relationships derived from the disdrometer measurements reflect the unusual characteristics of DSD during the flood. As a result, the standard NEXRAD Z-R relationship (Z = 300R1.4) strongly underestimated hourly rainfall by up to 27.5%. In addition, the empirical relations between rainfall kinetic energy (KE) versus rainfall intensity (R) and mean mass diameter (Dm) are also derived using DSDs to further investigate the impacts of raindrop properties on the rainfall erosivity.

Space-Temporary Analysis of External Geodynamic Disasters Occurred in Huaraz Province, Ancash - Peru

The natural disasters generated by external geodynamics are geological risks that constantly modify landscapes, with a more significant occurrence in mountainous areas, affecting populations and registering many victims in densely populated places. This research analyzes the events in Huaraz province, of Ancash department, in the central Andes of Peru, to find relationships between their occurrence and geographical factors such as altitude, slopes, climate, and extreme meteorological events. An inventory of events was made and classified as floods, mass gravitational movements, waterlogging or snow avalanches. Using QGIS software, spreadsheets and digital elevation models, information on natural disasters, altitude levels, physiography, river basins, meteorological data, and earthquakes were analyzed. As a result, it was obtained that the Quechua region registered 60% of all events; the Santa River basin 76%; the wet season of the Peruvian Andes 78%; and places with slopes between 8% and 50% (wavy relief) 72% of disasters. It is concluded that the best conditions for these events are the intense rainfall and the undulating reliefs, predominant in the Quechua region. Likewise, floods are the disasters that register the most significant number and generate the most damage in Huaraz province. Finally, it was determined that high-intensity El Niño-Southern Oscillation processes do not necessarily increase the number of events for the study area.

Comparative Evaluation of the Rainfall Erosivity in the Rieti Province, Central Italy, Using Empirical Formulas and a Stochastic Rainfall Generator

Soil erosion caused by intense rainfall events is one of the major problems affecting agricultural and forest ecosystems. The Universal Soil Loss Equation (USLE) is probably the most adopted approach for rainfall erosivity estimation, but in order to be properly employed it needs high resolution rainfall data which are often unavailable. In this case, empirical formulas, employing aggregated rainfall data, are commonly used. In this work, we select 12 empirical formulas for the estimation of the USLE rainfall erosivity in order to assess their reliability. Moreover, we used a Stochastic Rainfall Generator (SRG) to simulate a long and high-resolution rainfall time series with the aim of assessing its application to rainfall erosivity estimations. From the analysis, performed in the Rieti province of Central Italy, we identified three equations which seem to provide better results. Moreover, the use of the selected SRG seems promising and it could help in solving the problem of hydrological data scarcity and consequently guarantee major accuracy in soil erosion estimation.

Estimating return period of intense rainfall using Alexander's technique

After briefly describing the Alexander'e technique an attempt has been made to determine the return period of the highest one-day point rainfall in east Uttar Pradesh (U.P.) by using this technique. This study has shown that a point rainfall of 20 inches or more in one-day has a return period of about 2,000 years.

Characterization of the variability in climate extremes in the Ferkessédougou sugar complexes (Northern Côte d'Ivoire)

This study aims to analyse the frequency, intensity and duration of extreme climate events in order to optimise sugarcane production in the Ferkessédougou sugar complexes. The methodological approach is based on the calculation of extreme climate indices defined by the Expert Team on Climate Change Detection and Indices (ETCCDI) from daily rainfall and temperature data observed at the Ferké 2 station over the period 1999–2018. The results show that the rainfall indices are negative, except for the number of consecutive dry days (CDD); this shows a decreasing trend in rainfall with, however, insignificant trends. Over the period 1999–2006, the number of intense rainfall days (R10 mm) decreased from 40 to 28 d with an average decrease of 0.3 d yr−1 and the number of very intense rainfall days (R20 mm) fluctuated between 26 and 2 d, with a slope of 0.083. The extreme temperature indices show statistically significant positive trends for the warm sequences; this confirms the rising of temperatures on both a local and national scale. This study could enable the Ferkessédougou sugar complexes managers to develop strategies for adaptation to climate change.