Low Intensity Rainfall Events Research Articles

Towards transient connectivity of river networks during rainfall events: Insight from hydrological observation and functional data analysis

River connectivity, which is critical for river networks to perform their functions, is deteriorating in highly urbanized areas. While it is well known about the structural and functional connectivity of river networks using traditional indicators, much less is known about the process connectivity and its influence factor. To this end, we propose a new approach based on hydrological observations and functional data analysis that has the advantage of capturing transient changes in process connectivity and responses to rainfall events. Applying the method to a typical river-dense plain in China, the results show that 1) the highest and the lowest values of process connectivity were concentrated in 0.6–0.95 and 0.04–0.61during 2015–2020, respectively. The average values of process connectivity were lower in 2015, 2016, and 2020 with 0.49, 0.44, and 0.46, respectively, and higher in 2017 to 2019 with 0.52, 0.57, and 0.58, respectively. 2) There is a significant negative correlation between rainfall intensity and process connectivity, especially when heavy rainfall occurs. Under the same rainfall intensity, the process connectivity was weaker in the river network with lower structural connectivity, lower overflow capacity of main streams, strong concentration of rivers, more sluices and larger unit areas. 3) The main influencing factors on process connectivity were structural connectivity and rainfall, with contributions of 34.67% and 22.67%, respectively. Following closely are unit features and human regulation, contributing 14.07% and 12.61% to process connectivity, respectively. 4) Structural connectivity and unit features are the primary factors influencing process connectivity during low-intensity rainfall events. During high-intensity rainfall events, rainfall and unit features become the predominant factors affecting process connectivity. Our results provide a new insight for quantifying process connectivity in the plain and are expected to support the study of the changing mechanism of hydrological connectivity.

Assessment of satellite precipitation products at different time scales over a cyclone prone coastal river basin in India

Abstract Precipitation is a fundamental input for many hydrological and water management studies. With the advancement in science, a variety of satellite precipitation products are available. In this study, the ability of three satellite precipitation products (TRMM-3B42v7, PERSIANN-CDR and GPM-IMERGv6) to capture rainfall were evaluated with ground-based Indian Meteorological Department (IMD) gridded data and also by driving the Soil Water Assessment Tool (SWAT) hydrological model for a cyclone prone coastal river basin in the southeast of India. Results indicate that among the three, GPM-IMERG v6 outperformed in all the statistical metrics, followed by TRMM-3B42 v7 at different temporal scales. GPM-IMERG v6 exhibited the highest correlation coefficient (0.48) and lowest root mean square error (9.52 mm/day), followed by TRMM-3B42 v7 (CC = 0.44, RMSE = 9.58 mm/day) at daily scale. In contrast to other studies in similar regions, IMERGV6 showed better performance than the PERSIANN CDR in detection skills of low, medium and high intensity rainfall events as well as False Alarm Ratio. Hydrological evaluation of the three products using the SWAT model over the study area showed satisfactory results at daily and monthly scale during the calibration and validation period. IMERGV6 is found to have better performance in hydrological evaluation as well.

Driving Factors of Heavy Rainfall Causing Flash Floods in the Middle Reaches of the Yellow River: A Case Study in the Wuding River Basin, China

In the context of climate change, extreme rainfall events have greatly increased the frequency and risk of flash floods in the Yellow River Basin. In this study, the heavy rainfall and flash flood processes were studied as a system. Taking the driving factors of the heavy rainfall causing the flash floods as the main focus, the key factors of the heavy rainfall causing typical flash flood processes were identified, and the driving mechanism by which the heavy rainfall caused flash floods was revealed. Through comparative analysis of the rainfall related to 13 floods with peak discharges of greater than 2000 m3/s since measurements began at Baijiachuan hydrological station, it was found that different rainfall factors played a major driving role in the different flood factors. The factor that had the largest impact on the peak discharge was the average rainfall intensity; the factor that had the largest impact on the flood volume was the rainfall duration; and the factor that had the largest impact on the sediment volume was the maximum 1 h rainfall. The ecological construction of soil and water conservation projects on the Loess Plateau has had obvious peak-cutting and sediment-reducing effects on the flood processes driven by medium- and low-intensity rainfall events, but for high-intensity flash floods, the flood-reducing and sediment-reducing effects of these projects have been smaller. Therefore, despite the background of continuous ecological improvement on the Loess Plateau, the possibility of floods with large sediment loads occurring in the middle reaches of the Yellow River still exists.

Effects of tillage-induced soil surface roughness on the generation of surface–subsurface flow and soil loss in the red soil sloping farmland of southern China

The role of tillage-induced soil surface roughness (SSR) in altering surface–subsurface flow and soil loss needs to be investigated in the red soil region of southern China. In this study, two different roughness conditions (smooth surface and rough surface), produced by plowing with and without flattening, were employed to assess the effects of surface roughness on rainfall redistribution, surface and subsurface flow generation, and soil loss. In-situ rainfall simulations with three different rainfall intensities (30, 60, and 90 mm h−1) during 180 min of rainfall were tested for a steep farmland sloped at 15°. The results showed that the rough surface had a higher capability for improving subsurface flow, whereby 34% of the rainfall changed into surface flow, and 24% changed into subsurface flow; whereas the proportions of surface and subsurface flow on the smooth surface were 40% and 16%, respectively. The rough surface exhibited a faster initial generation of surface flow and subsurface flow, and the progress of erosion from sheet erosion to rill erosion was more rapid than on the smooth surface, leading to a higher sediment yield from the rough surface under stronger rainfall events. However, the rough surface demonstrated enhanced infiltration behavior and prevention of soil loss under low-intensity rainfall events. The difference in soil crusts on smooth and rough surfaces was the dominant factor affecting surface–subsurface flow generation and soil loss from the red soil sloping farmland. The roughness decreased on the rough surface and increased on the smooth surface during rainfall events. The interactions between surface and subsurface flow should be considered to evaluate soil loss; hence, this research provides a comprehensive understanding of the impact of tillage activities on soil erosion.

The influence of seed-drill choice on crop performance in a semi-arid production region of South Africa

A seed-drill should facilitate seed placement in an environment conducive to uniform seedling emergence. In semi-arid rain-fed production regions, low rainfall intensity and erratic rainfall events can result in non-uniform emergence. Evaluation of seed-drills is necessary to supply small grain producers with potential solutions to combat non-uniform seedling emergence. The aim of this study was to investigate the influence of three seed-drills on seeding depth, crop emergence, biomass production and yield over the duration of two growing seasons. Barley, canola and wheat were established with three seed-drills, each equipped with a different opener. Seed-drills contained either double disc openers, tine openers, or a combination of both tines and single discs. Crops responded variably to seeding equipment under different climatic conditions. For example, accuracy of seeding depth varied between the three seed-drills utilised. Seed-drills, together with their associated seed placement characteristics, influenced crop emergence. Biomass production was variable over the course of the growing season. Biomass production of crops established with the double disc seed-drill tended to be higher than that of crops established with tine seed-drills. Additional research about adaptations of agronomic practices and seed-drill openers may increase resilience to adverse climatic conditions in semi-arid small grain production regions. Various factors, including soil physical conditions, environmental conditions, economic feasibility and practical applications must be taken into consideration when selecting a seed-drill.

ASSESSMENT OF RESIDUAL SOIL PROPERTIES FOR SLOPE STABILITY ANALYSIS

Slope instability is a common natural geological hazard in tropical countries like Malaysia, with abundant residual soil and frequent rainfall. Over the years, these rainfalls have induced instabilities that lead to significant human and economic loss. To reduce the expected disastrous impacts due to rainfall-induced slope failure characterization of residual soil is necessary for evaluation of slope stability assessment. Therefore, this study aims to characterize the residual soil for numerical modelling of rainfall-induced slope failure and preliminary slope stability assessment so that future slope failure can be reduced. A series of experiments involving index properties tests and engineering properties tests were carried out on the residual soil samples collected from a slope located in UniversitiTeknologi Malaysia (UTM). Based on the particle size distribution and consistency the soil can be classified as high plasticity silt (MH). The maximum dry unit weight and optimum moisture content are 13.17kN/m3 and 30 %, respectively. Saturated hydraulic conductivity from the falling head test is 2.32055E-07 m/s, while the saturated gravimetric water content was 54%. The effective cohesion and angle of the internal fraction were 8 kPa and 32°, respectively. The average undrained shear strength and unconfined compressive strength were 105 kPa and 43 kPa, respectively. The result obtained in this study was utilized for the preliminary rainfall slope stability assessment in tropical residual soils by simulating rainfall of different intensities and duration on a typical slope profile using PLAXIS 2d. The results show that due to the low hydraulic conductivity and fine-grained nature of the soil, the slopes in the study area are more critical to the low intensity and long duration rainfall events (I≤4Ks). The highly intense and short-duration rainfall (I≥8Ks) has no significant effect on the safety of the soil, as most of the precipitation will contribute to runoff, and only a minor amount of water will infiltrate into the slope.

A comprehensive five-year evaluation of IMERG Late Run precipitation estimates over the Netherlands

AbstractApplications like drought monitoring and forecasting can profit from the global and near real-time availability of satellite-based precipitation estimates once their related uncertainties and challenges are identified and treated. To this end, this study evaluates the IMERG V06B Late Run precipitation product from the Global Precipitation Measurement mission (GPM), a multi-satellite product that combines space-based radar, passive microwave (PMW), and infrared (IR) data into gridded precipitation estimates. The evaluation is performed on the spatiotemporal resolution of IMERG (0.1° × 0.1°, 30 min) over the Netherlands over a five-year period. A gauge-adjusted radar precipitation product from the Royal Netherlands Meteorological Institute (KNMI) is used as reference, against which IMERG shows a large positive bias. To find the origin of this systematic overestimation, the data is divided into seasons, rainfall intensity ranges, echo top height (ETH) ranges, and categories based on the relative contributions of IR, morphing, and PMW data to the IMERG estimates. Furthermore, the specific radiometer is identified for each PMW-based estimate. IMERG’s detection performance improves with higher ETH and rainfall intensity, but the associated error and relative bias increase as well. Severe overestimation occurs during low-intensity rainfall events and is especially linked to PMW observations. All individual PMW instruments show the same pattern: overestimation of low-intensity events and underestimation of high-intensity events. IMERG misses a large fraction of shallow rainfall events, which is amplified when IR data is included. Space-based retrieval of shallow and low-intensity precipitation events should improve before IMERG can be implemented over the middle and high-latitudes.

Comparison of Soil Erosion Control by Mulch and Cultivated Grass

Soil erosion has deteriorated water quality and caused land degradation. As human industrialization quickens, the effects of soil erosion are getting worse. Therefore, it is essential to have an effective mitigation measure at hand to solve this problem. In this research, two types of erosion control methods were compared to determine their effectiveness in controlling soil erosion. The two methods used were mulch made from dried grass clippings and grass cultivation grown with Axonopus compressus or more commonly known as cow grass. The plots were placed under five rainfall events together with a control plot. The runoff volume, turbidity and total suspended solids (TSS) from the plot discharges were tested and compared. The effectiveness of each erosion control method under different rainfall conditions were also evaluated. Results indicated that the mulch plot produced a lower runoff volume but the grass plot did manage to improve performance over time. The turbidity of both plots were similar. The TSS produced by the grass plot was lower than the mulch plot in 4 out of the 5 testing periods. The grass plot also performed better in longer duration and high intensity rainfall events. The mulch was able to produce similar results with the grass in short duration, low or moderate intensity rainfall events. As a conclusion, the grass cultivation is a more effective erosion control method when compared to the mulch.

Recent Increase of Flood Frequency in the Ionian Belt of Basilicata Region, Southern Italy: Human or Climatic Changes?

The Ionian coast of the Basilicata region, southern Italy, is characterized by a remarkable archaeological heritage, valuable crops, and national and international tourism, contributing significantly to the regional economy. In the last two decades, the area has been affected by the heavy recurrence of flooding events, which caused significant damage to agriculture, tourist infrastructure, and archaeological heritage. Both qualitative and quantitative analyses of pluviometric, hydrometric, and erosion/deposition dynamics of main rivers have been carried out in order to investigate the role played by natural factors, climate changes, and human activity. The results show that flooding events in the Metaponto plain were certainly caused by extreme rainy events, but man has also played an important role. The Metaponto plain has been involved in a reclamation consisting of the building of an extensive channel network, which provided better land cultivation, easy access to the beaches, and archaeological heritage protection. The human impact related to the absence of channel cleaning has proved to be the most relevant factor that greatly amplified the effects of low-intensity rainfall events, thus triggering flooding events.

Hydrological behavior of a semi-dry forest in Northern Mexico: Factors controlling surface runoff

The understanding of the hydrological processes in transitional zones between semi-arid and temperate ecosystems is essential since these areas are particularly sensitive to changes in precipitation and land cover. The objectives were to (1) determine the most critical factors in the generation of surface runoff during one rainy season; and (2) analyze the effect of different rainfall variables and soil moisture on the amount of surface runoff. The study area is in a semi-dry forest in the state of Chihuahua, Mexico. Vegetation, soil, and precipitation variables were monitored on three micro-catchments (0.19–0.27 ha) in 2018. Maximum 30-min rainfall intensity, rainfall depth, and soil moisture were the main variables controlling surface runoff. Rainfall intensity was better related to the amount of surface runoff, with an increase in runoff when rainfall intensities were greater than 25 mm h−1. The highest runoff coefficients (10%) occurred only when rainfall intensity exceeded 30 mm h−1. Similarly, surface runoff was only activated when rainfall depth exceeded 20 mm, or when the maximum volumetric water content by rainfall event exceeded 30%. Only 10% of storms exceeded these thresholds, indicating the difficulty of runoff generation in transitional zones. The interception (36%; s.d. = 30.7%), and the drastic decrease in soil moisture after each storm, suggest that more than 90% of the rainfall was lost by evapotranspiration. Our findings suggest that the groundwater recharge in a given year in these transitional zones is highly related to the number of low intensity and long duration rainfall events.

Characteristics of southwest summer monsoon rainfall events over East India

The variability in Indian summer monsoon rainfall (ISMR) has an immense socioeconomic impact on India, especially over the monsoon core region. In this study, a thorough analysis of the ISMR (June to September—JJAS) has been performed for East India (EI), a part of the monsoon core zone, and for its four subdivisions (Odisha, Chhattisgarh, Jharkhand, and Bihar). The long-term climatology, variability, and trends of various categorical rainfall events as defined by India Meteorological Department (IMD) have been analyzed by using IMD high-resolution (0.25° × 0.25°) gridded dataset for 116 years (1901–2016). Also, the percentage contribution of various rainfall events to the total seasonal rainfall and wet days is estimated. To get the changes in the frequency of various dry spells, rainfall events, and associated seasonal rainfall, study period is divided into two halves, earlier period (P1: 1901–1958) and recent period (P2: 1959–2016). The results suggest that the percentage contribution of medium-intensity rainfall events (7.6–64.4 mm/day) to the total ISMR is higher (~ 72%) followed by high-intensity rainfall events (~ 15%) and low-intensity rainfall events (12%), while most percentage contribution to the total number of wet days is from low-intensity rainfall events (~ 54%) followed by medium-intensity rainfall events (~ 43%) and high-intensity rainfall events (~ 3%). In the recent period (P2), the ISMR significantly decreased over the central part of EI because of the significant decrease in the frequency of low and medium-intensity rainfall events and wet days. The remarkable decrease of wet days leads to an increase in the short (1 week) and long-duration (> 2 week) dry spells in P2. And at the same time, high-intensity rainfall events significantly increased over EI in the recent period (P2) and led to an increase in the flood situation over this region. The profound relation of deficit rainfall of EI with ENSO is getting weak in the P2. This study is certainly useful in determining the effects on various sectors because of the variability and changes in various categorical extreme rainfall events, short and long-duration dry spells during summer monsoon time over EI. Also, this study may assist the risk management sectors in acclimating advanced technologies for a sustainable future in the changing climate of the present global warming era.

Application of stabilized sludge to extensive green roofs in Shanghai: Feasibility and nitrogen leaching control

Extensive green roofs, in which commercial compost is usually used as organic component, have great potential to mitigate some environmental problems caused by urbanization, but carry risks of nutrients leaching into downstream aquatic. Stabilized sludge (SS) from wastewater treatment plants could be potentially used as nutrient component for green roof, but the effects on effluent quality are uncertain. To investigate the problem, a pilot experiment was conducted under field conditions, the effluent quality of green roof using SS was compared with green roofs using peat soil and controlled release fertilizer. In the field experiment, the nutrient concentrations in effluent of the green roof using SS (TN, NO3−-N, NH4+-N and TP were 3.27 mg/L, 1.75 mg/L, 1.14 mg/L and 0.34 mg/L, respectively) were not significantly different from the green roofs using peat soil and controlled release fertilizer, and the chemical oxygen demand level (92 mg/L) was lower than the roofs using compost or commercial substrate. To reduce the environmental risks caused by the application of SS to green roofs, a laboratory test was carried out to analyze the effects of biochar and dual-substrate structure on nitrogen leaching. The results showed that both biochar and dual-substrate reduced nitrogen leaching, and nitrogen leaching from green roofs using SS was a combined effect of organic nitrogen mineralization during dry period and biological processes during wet period. A high temperature and low humidity environment which is common in green roofs reduced nitrate accumulation during dry period, and nitrate was transformed to other substances in gaseous form by denitrification, which tended to occur in long duration, low intensity rainfall events. The results suggest that the application of stabilized sludge to green roofs is feasible in area where average rain intensity is not high, preferably combined with amendment of biochar and a dual-substrate structure.

On the uniformity of rainfall distribution over India

Understanding response of temporal distribution, timing, frequency and amount of high and low intensity rainfall to warming is important in water resources management. In this paper, Relative Entropy is used to investigate the spatial variability and change in uniformity of rainfall distribution over India. Temporal trends in atmospheric temperature can alter the frequency and amount of high and low intensity rainfall events, which influence the uniformity of rainfall distribution. The study is divided into two time periods, 1951–1980 and 1981–2010 based on time trend in annual mean temperature. The sensitivity of rainfall uniformity and high and low intensity rainfall events to annual mean temperature and the degree of coherence between them are investigated. The uniformity of rainfall distribution shows a significant spatial variability. Significant changes are observed in both the amount and timing of rainfall across India. A significant association between rainfall uniformity and low intensity of rainfall is observed in the recent past over a larger aerial extent compared to the distant past. It is concluded that rise in temperature modifies both high and low intensity rainfall events, thus altering the uniformity in rainfall distribution. A regionally varied strength of coherence between rainfall uniformity and high and low intensity rainfall is observed which may be due to regionally dependent soil moisture-precipitation feedbacks.

Effect of rainfall infiltration on the hydraulic response and failure mechanisms of sandy slope models

This paper presents experimental results obtained from silty sand slope models subjected to an artificial rainfall. Four models were constructed to evaluate the effect of initial water content and rainfall intensity on the hydraulic behavior and failure mechanisms of the slopes. The models were instrumented with volumetric water content sensors to monitor the advance of the water front, and inclinometers to measure lateral movements of the slope. The models were subjected to rainfall intensities ranging from 25 to 50 mm/h, and durations from 19 to 152 minutes. The influence of low intensity rainfall events before a high intensity rainfall is discussed herein. The results showed that the time the slope models required to reach failure was influenced by the soil initial water content, being shorter at high initial water contents. These results are useful to understand the behavior of unsaturated natural slopes and embankments exposed to rainfall infiltration, and to complement the existing laboratory database existing in this subject.

Vegetation Response to Burn Severity, Native Grass Seeding, and Salvage Logging

AbstractAs the size and extent of wildfires has increased in recent decades, so has the cost and extent of post-fire management, including seeding and salvage logging. However, we know little about how burn severity, salvage logging, and post-fire seeding interact to influence vegetation recovery long-term. We sampled understory plant species richness, diversity, and canopy cover one to six years post fire (2006 to 2009, and 2011) on 72 permanent plots selected in a stratified random sample to define post-fire vegetation response to burn severity, post-fire seeding with native grasses, and salvage logging on the 2005 School Fire in eastern Washington. Understory vegetation responded rapidly post fire due, in part, to ample low intensity rainfall events in the first post-fire growing season. Vegetation was more diverse with greater plant species richness and diversity (Shannon-Wiener index) in low and moderate burn severity plots in 2006 (species richness 18; diversity 2.3) compared to high burn severity plots (species richness 10; diversity 1.8), with species richness on the high severity plots reaching 19 in the sixth post-fire year, similar to the initial values on the low and moderate burn severity plots. Plants that commonly resprout from rhizomes, bulbs, and other surviving belowground sources were abundant post fire, while those establishing from off-site seed sources, including non-native species, were present but not abundant. Plots seeded with native grass post fire and not salvage logged had the highest canopy cover of graminoid species: more than 30 % six years after the fire (in 2011), with low forb (15 %) and shrub (1 %) canopy cover and species richness. For comparison, high severity plots that were not seeded and not salvage logged had 3 % graminoid cover, 14 % forb cover, and 26 % shrub cover. Plots that had been salvage logged from one to three years after the fire produced less canopy cover of shrubs and forbs, but three times more canopy cover of graminoids on the high burn severity plots by 2011. High severity plots that were salvage logged and not seeded with native grasses had the lowest species richness, diversity, and cover. Very few non-native species were found, regardless of salvage logging and seeding. Rapid post-fire growth dominated by native plants of high diversity suggests that this forest’s vegetation and soils are highly resilient to disturbance. Overall, burn severity and post-fire seeding with native grasses were more influential than salvage logging on understory plant abundance one to six years after fire.

Controls on sediment production from an unpaved resource road in a Pacific maritime watershed

AbstractUnpaved resource roads have the potential to produce large amounts of sediment and can negatively impact water quality and aquatic ecology. In order to better understand the dominant controls on sediment generation from unpaved resource roads, we did 23 large‐scale rainfall simulation experiments on a road section in the Honna Watershed, Haida Gwaii, British Columbia, Canada. The experiments were performed with different rainfall intensities (4–52 mm/h), with and without traffic. Precipitation intensity was the dominant control on the amount of sediment generated from the road surface; the total mass of sediment increased linearly with precipitation intensity. The number of passages of loaded logging trucks during an experiment was the second most dominant control on the total amount of sediment generated from the road surface. Elevated sediment concentrations in road surface runoff persisted for 30 min following the passage of loaded logging trucks during low intensity (<8 mm/h) rainfall events and for much shorter periods at higher rainfall intensities. The mass of sediment generated by the passage of a loaded truck increased with precipitation intensity. Passages of empty logging truck did not result in sediment pulses, except during very high rainfall intensities. Seven small‐scale rainfall simulation experiments on other parts of the road, however, highlight the large spatial variability in sediment production from the road surface, suggesting additional experiments are required to better describe and predict sediment production from different road sections.

Characterising nutrients wash-off for effective urban stormwater treatment design

This paper characterises nitrogen and phosphorus wash-off processes on urban road surfaces to create fundamental knowledge to strengthen stormwater treatment design. The study outcomes confirmed that the composition of initially available nutrients in terms of their physical association with solids and chemical speciation determines the wash-off characteristics. Nitrogen and phosphorus wash-off processes are independent of land use, but there are notable differences. Nitrogen wash-off is a “source limiting” process while phosphorus wash-off is “transport limiting”. Additionally, a clear separation between nitrogen and phosphorus wash-off processes based on dissolved and particulate forms confirmed that the common approach of replicating nutrients wash-off based on solids wash-off could lead to misleading outcomes particularly in the case of nitrogen. Nitrogen is present primarily in dissolved and organic form and readily removed even by low intensity rainfall events, which is an important consideration for nitrogen removal targeted treatment design. In the case of phosphorus, phosphate constitutes the primary species in wash-off for the particle size fraction <75 μm, while other species are predominant in particle size range >75 μm. This means that phosphorus removal targeted treatment design should consider both phosphorus speciation as well as particle size.

Temporal variation of heavy metal pollution in urban stormwater runoff

Stormwater runoff from three types of urban surfaces, a parking lot, a street, and a building roof, was monitored during four rainfall events that occurred in the one-year period from June 2009 to June 2010. The event mean concentrations (EMC) of dissolved copper (Cu), lead (Pb), zinc (Zn), manganese (Mn), and iron (Fe) exceeded China’s National Water Quality Standards for Surface Water. The degree of heavy metal contamination was related to the type of underlying surfaces. Additionally, the concentration of dissolved heavy metals peaked shortly after the runoff began and then declined sharply as a result of adequate flushing. First flush effects of varying degrees were also observed during all of the monitored rainfall events based on the first flush ratio (FF25). Redundancy analysis revealed that four environmental variables (rainfall depth, intensity, antecedent dry weather period and type of underlying surface) had significant effects on the strengths of the first flush effects, accounting for 72.9% of the variation in the FF25. Dissolved metals presented varying first flush effects on different underlying surfaces that occurred in the following relative order: parking lot>roof>road for low intensity and high runoff volume rainfall events; parking lot>road>roof for high intensity and low runoff volume events. The relative strength of the first flush for dissolved heavy metals was Fe, Mn>Cu, Zn>Pb.

Nature of light rain during presence and absence of bright band

This paper reports the evolution of rain drop size distribution (DSD) during bright band (BB) and no-BB (NBB) conditions of low intensity rainfall events as observed by a vertically pointing Micro Rain Radar (MRR) over Pune (18.58°N, 73.92°E), India. The BB is identified by enhanced radar reflectivity factor Z (dBZ) at the 0°C isotherm. The gradient of hydrometeor fall velocity is found to be a good indicator in identifying the melting layer when enhanced radar reflectivity at melting layer is not prominent. The storm structures as observed by the MRR are compared with CloudSat observations that provide evidence of ice hydrometeor at ~ −60°C with clear indication of BB at 0°C. Storm heights at warmer than 0°C are evident during NBB conditions from CloudSat. This suggests that warm rain processes are responsible for producing rain during NBB conditions. During BB conditions, bimodal DSDs below the melting layer are observed at lower altitudes. The DSDs of shallow warm precipitating systems of NBB conditions are monomodal at all the altitudes. Significantly, normalized DSDs are found to be bimodal for BB conditions, and monomodal for NBB conditions which confirm different dominant microphysical processes. It is found that the observed bimodal DSDs during BB conditions are mainly due to the collision, coalescence and break-up processes. During NBB conditions, number and size of large raindrops grow while reaching the ground without much breakup. The radar reflectivity and rainfall intensity R (mmh − 1) relationship of the form Z = aR b are found out for BB and NBB conditions. Existing different microphysical processes lead to large coefficient in the Z–R relationship with small exponent during BB conditions while during NBB conditions the coefficients are small with large exponents.

Runoff at contrasting scales in a semiarid ecosystem: A complex balance between biological soil crust features and rainfall characteristics

Runoff in arid and semiarid areas is characterized by high spatial and temporal variability. The spatial component is largely associated with the high spatial heterogeneity of soil surface attributes, such as vegetation and rock fragment covers, topography, and soil crust typology. Biological soil crusts (BSCs) are a common soil cover in arid and semiarid areas, and they play an essential role in local hydrological processes, since they affect many soil surface attributes associated with hydrologic properties. Although several publications have reported on the influence of BSCs on runoff at microplot spatial scales, only a few have examined their influence on larger spatial scales. Moreover, very few studies have analyzed the effect of BSCs on runoff under natural rain conditions. This is difficult, since a complex pattern of interactions among rainfall properties, BSC characteristics and some local characteristics, such as topography or type of soil is expected. In addition, in order to achieve a realistic model of how BSCs and rainfall affect runoff, it would be necessary to consider the level of human-driven degradation of BSCs. In this study, runoff was analyzed in plots with varying cover of cyanobacterial and lichen BSCs at microplot and small hillslope scales for two hydrological years in badlands in SE Spain. Structural equation modelling (SEM) was applied to test both direct and indirect relationships of BSC cover, slope gradient, rainfall characteristics and runoff. Our model showed that rainfall characteristics were the main factors controlling runoff yield. The slope positively affected runoff at small hillslope scales, but did not influence runoff at microplot scales. Runoff decreased at both scales with increased lichen-BSC cover. However, this effect was only significant during low-intensity events. Under high rainfall intensities, neither the BSC cover nor the slope had a causal effect on runoff. Our results suggest that incorporation of BSC-crusted surfaces in models should improve their capabilities for low-intensity rainfall events in semiarid areas similar to ours, but would be less important for high-intensity events. In addition, our approach, which takes direct and indirect relationships of factors affecting runoff into consideration, provides a very accurate picture of the process.