Significant Rain Events Research Articles

Effect of intra-seasonal variation in precipitation on seed germination and seedling growth in Iris atrofusca: implications for conservation

Abstract Understanding the modulating effect of environmental conditions on the germination of seeds constituting a persistent soil seed bank has both theoretical and practical merits. I studied the role of precipitation in the germination of seeds of the imperiled geophyte Iris atrofusca, which exhibits strong seed dormancy and intermittant germination over years. I wanted to know how a single significant rain event in one of the first several seasons after seed maturation and dispersal can affect seed germination and seedling growth in I. atrofusca. This is important because knowing the amount and time of such a rainfall event, one can imitate it by a single watering applied to an artificial soil seed bank, thus initiating or substantially increasing seed germination and improving seedling growth and therefore survival. Overall, the results imply that the most efficient in terms of both seed germination and seedling survival is supplementary irrigation equivalent to 40 mm rainfall applied as a single rain event to the artificial soil seed bank early in the first and second season, plus watering equivalent to 20–40 mm in the months when the amount of precipitation is low (below 20 mm) not only in the first and second, but also in subsequent seasons.

The NRCS Peak Rate Factor for Severe Storms

AbstractThe Natural Resources Conservation Service's Dimensionless Unit Hydrograph is used extensively in industry by design engineers for the purpose of determining the runoff hydrograph from a rainfall event. As part of the methodology, the user is required to input a Peak Rate Factor (PRF) which describes the runoff response (volume distribution) of the corresponding unit hydrograph. Unfortunately, little guidance is given in the literature for selecting an appropriate PRF for a given watershed. Additionally, consideration has not been given to determine if the PRF should remain constant for a given watershed or be allowed to vary as a function of return period. The goal of this study was to back‐calculate site‐specific PRFs for various watersheds which have experienced two or more significant rain events since the year 2000. A total of 14 watersheds were investigated with results showing PRFs remained consistent for five of the watersheds regardless of the storm event. Nine of the watersheds showed a significant variation in PRF with an average variation of approximately 440 across all storm events within a given watershed. Additional analysis showed there is a general trend of increasing PRF with decreasing storm‐specific curve number. Finally, the complacent‐violent runoff response was shown to occur for storms with resulting PRF's in excess of 1,000.

Harmful Algal Bloom Species in the St. Martin River: Surveying the Headwaters of Northern Maryland's Coastal Bays

Wolny, J.L.; McCollough, C.B.; Rosales, D.S., and Pitula, J.S., 2022. Harmful algal bloom species in the St. Martin River: Surveying the headwaters of northern Maryland's coastal bays. Journal of Coastal Research, 38(1), 86–98. Coconut Creek (Florida), ISSN 0749-0208. In the spring seasons of 2015 through 2017, the Maryland Department of Natural Resources and the University of Maryland Eastern Shore monitored the phytoplankton community of the headwaters of the St. Martin River, a tributary at the northern end of Maryland's coastal bays, to determine the presence and extent of harmful algal bloom (HAB) species. The phytoplankton community composition, including HAB species, was examined via weekly sampling from March through June. In 2015, HAB events began in late March with a bloom of Gymnodinium aureolum, representing the first report of this species in Maryland waters. Following the G. aureolum bloom, blooms of other HAB species occurred, including Dinophysis acuminata, Karlodinium veneficum, Prorocentrum minimum, and a species in the Alexandrium minutum complex. Initiating at the NW extent of the St. Martin River, these blooms became distributed both temporally and spatially throughout the study area. These same species were detected in 2016 and 2017 but at lower concentrations than those seen in 2015. High concentrations and diverse blooms of HAB species in 2015 may have been due to significant rain events and/or an increase in ammonium levels from a legacy nutrient pool following the removal of the Bishopville Dam, located upstream of the study site in November 2014. This study provides a baseline assessment for future work on harmful algae in the St. Martin River watershed and a look into phytoplankton community dynamics after a dam removal.

Trace Elements and Their Variation with pH in Rain Water in Arid Environment.

Climate change in Kuwait has resulted in temperature fluctuations, frequent dust storms, and noticeable changes in the amount of precipitation. Pollutants released into the atmosphere from various sources affect the chemical composition of rainwater and impact its usability. The present study on rainwater focused on the determination of trace elements, sources, and their variation with respect to change in temperature and pH. The samples were collected from 12 different locations in both industrial and urban regions during significant rain events (n = 31) from November 2018 to March 2019and samples were analyzed for trace elements in ICP-OES using standard USEPA 200.7 method. The mean concentration of the 16 elements analyzed followed the trend: Co < Cd < Cr < Mo < V<Ni < Pb < As < Se < Fe < Cu < Mn < Zn < Al < Ba < Sr and were inferred to be within the WHO permissible limits of drinking water. The analytical results revealed that Strontium (Sr) had the highest mean concentration (188μg/L) followed by barium (Ba), aluminum (Al), and zinc (Zn) with mean concentrations of 95.2μg/L, 30.4μg/L, and, 16.6μg/L respectively. The sources of contamination in rainwater were identified by calculating the enrichment factor (EF) using element concentration reported in Kuwait dust and from continental crustal values. EF for Fe, V, Ni, and Cr were below 10, indicating purely crustal sources. Ni, Zn, Cu, and Mn exhibited values between 10 and 100, reflecting industrial sources of contamination. EF for Sr was greater than 100, due to inputs from anthropogenic sources. A strong association between Al and pH along with correlation between Sr, Cr, Cu, Ni, Mo, V, and meteorological parameters was revealed from statistical analysis. Furthermore, pH Redox Equilibrium C programming (PHREEQC) was used to simulate changes in pH and temperature in rainwater to predict the resultant variations in trace element concentrations. There was no significant change observed in pH with rise in temperature, but the concentration of trace elements varied with change in pH. The concentration of V, Cr, and Al were most sensitive to pH variations. The results indicated that industrial emissions, fuel combustion, and dust in Kuwait are the primary sources of Al, Sr, Mn, Zn, and Ba in the rainwater samples. Since, the concentrations of these elements are relatively low, rainwater in Kuwait could be harvested for drinking and domestic purposes and used for recharging aquifers.

Consequences of drought severity for tropical live oak (Quercus oleoides) in Mesoamerica.

In two Costa Rican and three Honduran sites that vary in rainfall and soil properties, we used natural isotopes, a soil water balance model, and broad-scale climate-based drought indices to study shifts in water use with ontogeny from seedlings to mature tropical live oak (Quercus oleoides) trees. Water use patterns help to explain persistence of this broadly distributed species in Mesoamerica and to evaluate likely threats of ongoing climate changes. At the end of the dry season, soil δ18 O profiles can be described by one-phase exponential decay curves. Minimum values reflect geographic origins of the last significant rain event, and curvature is inversely related to canopy closure, demonstrating its role in controlling topsoil evaporation. Partitioning of soil water sources for transpiration was analyzed with a mixing model. In the Costa Rican sites, in a relatively dry year, saplings and mature trees took up water from the upper soil. In a relatively wet year in the Honduran sites, we observed deeper water extraction. In all sites, soil storage dampens extreme variation in water availability. The size dependence of water uptake with larger stems exploiting deeper layers is translated into variation in bulk leaf δ13 C-based water use efficiency (WUE) with the exception of mature trees. From 1932 to 2015, drought severity was evaluated with the Standardized Precipitation Evapotranspiration Index (SPEI) concurrently with simulations of the soil water balance model. Drought occurrence increased, regardless of the time period, averaged across 6, 12, or 24months. All ontogenetic stages in all populations experienced frequent water limitation. We found evidence for linear trends toward aridification with increases of return periods of drought for October SPEI-24 declining from 42 to 6yr in Costa Rica and from 21 to 7yr in Honduras and recent occurrence of multiyear droughts from 2013 to 2016. October SPEI-12 and SPEI-24 were significantly related to the Oceanic Niño Indices demonstrating that local inter-annual variations in drought severity in Mesoamerica are modulated by large-scale climate forces. Drought severity in the near-term future depends on the extent to which the Pacific will adopt a more La Niña-like vs. a more El Niño-like state under ongoing climatic changes.

Drought tolerance of a Pinus palustris plantation

Longleaf pine (Pinus palustris Mill.) forests are thought to be drought tolerant and if so, planting longleaf pine presents a forest management strategy for climate change adaptation in the southeastern United States (U.S.). To better understand how longleaf pine copes with drought, leaf water relations, sap flow, canopy stomatal conductance (GS), and growth were studied over three growing seasons in response to ambient throughfall (ambient treatment) versus an approximate 40% reduction in throughfall (drought treatment) in a 13-year-old plantation. An exceptional drought occurred the first year of the study and decreased mean predawn (ΨPD) and midday (ΨMD) leaf water potential to −2.9 MPa and −3.6 MPa, respectively, and decreased average monthly midday Gs to near zero for at least one month in both treatments. Stomatal closure occurred at a ΨMD of −3.0 MPa in both treatments. Leaf water potentials and transpiration recovered quickly following significant rain events that terminated the drought and mortality was similar among years and treatments (2.8%). Longleaf pine responded to drought treatment with greater stomatal control of plant water loss rather than adjustments in leaf area, the sapwood to leaf area ratio, or leaf water potential at the turgor loss point (ΨTLP). Annual transpiration per unit leaf area was reduced 16% by drought treatment, but greater stomatal control of water loss in response to drought treatment was associated with decreases in growth efficiency and volume, and no improvement in water use efficiency.

Displacement mechanisms of slow-moving landslides in response to changes in porewater pressure and dynamic stress

Abstract. Although slow-moving landslides represent a substantial hazard, their detailed mechanisms are still comparatively poorly understood. We have conducted a suite of innovative laboratory experiments using novel equipment to simulate a range of porewater pressure and dynamic stress scenarios on samples collected from a slow-moving landslide complex in New Zealand. We have sought to understand how changes in porewater pressure and ground acceleration during earthquakes influence the movement patterns of slow-moving landslides. Our experiments show that during periods of elevated porewater pressure, displacement rates are influenced by two components: first an absolute stress state component (normal effective stress state) and second a transient stress state component (the rate of change of normal effective stress). During dynamic shear cycles, displacement rates are controlled by the extent to which the forces operating at the shear surface exceed the stress state at the yield acceleration point. The results indicate that during strong earthquake accelerations, strain will increase rapidly with relatively minor increases in the out-of-balance forces. Similar behaviour is seen for the generation of movement through increased porewater pressures. Our results show how the mechanisms of shear zone deformation control the movement patterns of large slow-moving translational landslides, and how they may be mobilised by strong earthquakes and significant rain events.

Inundation Patterns of Farmed Pothole Depressions with Varying Subsurface Drainage

HighlightsFarmed pothole depressions in the Des Moines Lobe were observed to fill due to runoff and shallow subsurface flow.Six of the eight observed potholes flooded for five or more days some time during the two years of observation.Subsurface drainage and surface inlets reduced but did not prevent yield-limiting flooding in the observed potholes. Abstract. The prairie pothole region (PPR) ranges from central Iowa to the northwest into Montana and south central Canada, totaling around 700,000 km2. This area contains millions of potholes, or enclosed topographical depressions, which often inundate with rainfall. Many are located in areas that have been converted to arable agricultural land through installation of artificial drainage. However, even with drainage, potholes will pond or have saturated soil conditions during and after significant rain events. The portion of the PPR that extends into Iowa is known as the Des Moines Lobe. In this two-year study, surface water depth data were collected hourly from eight prairie potholes in the Des Moines Lobe in central Iowa to determine the surface water hydrology. These potholes included surface and subsurface drained row crops and undrained retired land, allowing for drainage comparisons. Inundation lasted five or more days at least once at six of the eight potholes, including four potholes with surface inlets and subsurface drainage, which resulted in four of fourteen growing seasons not producing a yield in part of the pothole. Water balances of four different drainage intensities showed increased infiltration due to subsurface drainage and up to 78% of outflow due to surface inlet drainage. Overall, drainage decreased the number of average inundation days, but heavy precipitation events still caused lengthy inundation periods that resulted in crop loss. Keywords: Farmed wetlands, Prairie pothole, Tile drainage, Water balance.

Seasonal and Intra-Event Nutrient Levels in Farmed Prairie Potholes of the Des Moines Lobe

HighlightsNitrogen, total phosphorus, and total suspended solids concentrations were higher in early season inundation.Nitrate concentrations in farmed potholes decreased with multiday ponding.Farmed potholes act as hotspots, contributing P to drainage through surface intakes.Abstract. The prairie pothole region ranges from central Iowa to the northwest into Montana and south-central Canada, totaling around 700,000 km2. This area contains millions of potholes, or enclosed topographical depressions, which often inundate with rainfall. Many are located in areas that have been converted to agricultural land through installation of artificial drainage. However, even with drainage, potholes pond or remain saturated during and after significant rain events. In this two-year study, surface water depth was collected hourly (typically from after planting through harvest) from eight farmed potholes (drained and under corn-soybean rotation) on the Des Moines Lobe in central Iowa. Nutrient data were collected daily and tested for nitrogen (N) and phosphorus (P) when inundation depth exceeded 10 cm. The data were analyzed in two ways. First, seasonal differences were investigated using samples from the first day of each inundation event. Surface water concentrations were higher in the early growing season than late season for total N (TN), NO3-N, NH3-N, total P (TP), and total suspended solids (TSS). Secondly, average event concentration changes were determined. Nitrate reductions occurred in 85% of multiday events, but these reductions were offset by increases in P. Total P and dissolved reactive P (DRP) had significant increases that averaged 0.51 and 0.46 mg L-1 per event, respectively, with event lengths of 2 to 19 days. This study demonstrates that inundated farmed potholes reduce NO3-N but serve as in-field hotspots, contributing elevated TP and DRP to drainage waters. When a surface intake directly connects inundated farmed potholes to drainage, new strategies, such as field management or engineered technologies, are needed to mitigate P export. This study is useful in informing policy regarding field management and conservation of farmed potholes. Keywords: Farmed wetland, Nitrogen, Nutrients, Phosphorus, Prairie pothole.

Seasonal variation of subsurface flow pathway spread under a water repellent surface layer

In water repellent soils, infiltration following dry periods will typically be limited to narrow pathways which enlarge gradually through winter to produce seasonal patterns of progressive water repellent breakdown. Simple, one-dimensional hydrological models, which assume moisture is horizontally uniform, will not produce representative results in soils where preferential flow dominates, but may produce good representations of moisture dynamics at late stages of the wet season, where declining water repellency has allowed pathways to spread to their maximum extent, producing flow which is close to homogeneous in nature. We propose a new metric, the Mean Modified Response or MMR, to quantify intermediate stages of seasonal water repellent breakdown in terms of the discrepancy between field data and a calibrated one-dimensional model representing the same soil in a hydrophilic state. The utility of this metric is demonstrated using four years of soil moisture sensor data collected at a woodland site in Perth, Australia with a highly water repellent A-horizon. Individual rain events were simulated using data from an on-site rain gauge.MMR results show strong seasonal trends in all years of study, comparable to those revealed by an older metric, the Effective Cross Section, which provides a measure of flow heterogeneity. However, the new MMR metric is particularly useful for identifying variations in soil moisture responses by depth. We show that the highly water repellent surface layer diverts moisture preferentially to deeper layers to produce increasing moisture responses at depth, in patterns which sharply contrast with model predictions. This effect is shown to decrease through winter as surface repellency breaks down, but may be highly significant in conserving moisture against evaporative loss during dry periods. Results of the MMR analysis suggest that soil was most successful in diverting flow to deeper layers in periods where significant rain events were separated by dry periods of at least a week, but less successful where rain events were either highly isolated or closely spaced. We conclude that comparison to the 1D model presents a useful tool in demonstrating how patterns of infiltration are altered under water repellent conditions.

A Multiplicative Cascade Model for High‐Resolution Space‐Time Downscaling of Rainfall

AbstractDistributions of rainfall with the time and space resolutions of minutes and kilometers, respectively, are often needed to drive the hydrological models used in a range of engineering, environmental, and urban design applications. The work described here is the first step in constructing a model capable of downscaling rainfall to scales of minutes and kilometers from time and space resolutions of several hours and a hundred kilometers. A multiplicative random cascade model known as the Short‐Term Ensemble Prediction System is run with parameters from the radar observations at Melbourne (Australia). The orographic effects are added through multiplicative correction factor after the model is run. In the first set of model calculations, 112 significant rain events over Melbourne are simulated 100 times. Because of the stochastic nature of the cascade model, the simulations represent 100 possible realizations of the same rain event. The cascade model produces realistic spatial and temporal patterns of rainfall at 6 min and 1 km resolution (the resolution of the radar data), the statistical properties of which are in close agreement with observation. In the second set of calculations, the cascade model is run continuously for all days from January 2008 to August 2015 and the rainfall accumulations are compared at 12 locations in the greater Melbourne area. The statistical properties of the observations lie with envelope of the 100 ensemble members. The model successfully reproduces the frequency distribution of the 6 min rainfall intensities, storm durations, interarrival times, and autocorrelation function.

Evaluation of the novel crAssphage marker for sewage pollution tracking in storm drain outfalls in Tampa, Florida

CrAssphage are recently-discovered DNA bacteriophages that are prevalent and abundant in human feces and sewage. We assessed the performance characteristics of a crAssphage quantitative PCR (qPCR) assay for quantifying sewage impacts in stormwater and surface water in subtropical Tampa, Florida. The mean concentrations of crAssphage in untreated sewage ranged from 9.08 to 9.98 log10 gene copies/L. Specificity was 0.927 against 83 non-human fecal reference samples and the sensitivity was 1.0. Cross-reactivity was observed in DNA extracted from soiled poultry litter but the concentrations were substantially lower than untreated sewage. The presence of the crAssphage marker was monitored in water samples from storm drain outfalls during dry and wet weather conditions in Tampa, Florida. In dry weather conditions, 41.6% of storm drain outfalls samples were positive for the crAssphage marker and the concentrations ranged from 3.60 to 4.65 log10 gene copies/L of water. After a significant rain event, 66.6% of stormwater outlet samples were positive for the crAssphage marker and the concentration ranged from 3.62 to 4.91 log10 gene copies/L of water. The presence of the most commonly used Bacteroides HF183 marker in storm drain outfalls was also tested along with the crAssphage. Thirteen samples (55%) were either positive (i.e., both markers were present) or negative (i.e., both markers were absent) for both the markers. Due to the observed cross-reactivity of this marker with DNA extracted from poultry litter samples, it is recommended that this marker should be used in conjunction with additional markers such as HF183. Our data indicate that the crAssphage marker is highly sensitive to sewage, is adequately specific, and will be a valuable addition to the MST toolbox.

SMOS Near-Surface Salinity Stratification Under Rainy Conditions

The European Space Agency’s soil moisture ocean salinity (SMOS) satellite was launched in 2009 to measure land soil moisture and sea surface salinity (SSS). It carries an L-band microwave imaging radiometer that measures brightness temperatures that are used to produce global ocean salinity (OS) maps every three days. Similar maps are obtained with NASA’s L-band push-broom radiometer Aquarius (AQ) on board of the AQ/SAC-D satellite that was launched in 2011. In previous studies, the Central Florida Remote Sensing Laboratory (CFRSL) has analyzed AQ SSS retrievals during rain and has developed a model to predict the effect of precipitation on the SSS measurements. This rain impact model (RIM) estimates the transient near-surface salinity stratification based upon the corresponding rain accumulation over the previous 24 h to the satellite observation. In this paper, the RIM methodology has been adapted to the SMOS geometry, presenting comparisons with its SSS measurements; also, spatial correlations are performed between SMOS salinity images with those predicted by RIM for different wind speed ranges. Therefore, the main objective of this research is to better understand the processes of near-surface salinity stratification, which impact the interpretation of satellite-based SSS measurements to measure the ocean bulk salinity (5–10-m depth). The results presented in this paper show an excellent performance of RIM when applied to SMOS SSS data. Also, the SSS comparisons show that significant rain events are rapidly diluted for wind speeds of $\sim 12 \text{ m}/\text{s}$ and above.

New algorithm for integration between wireless microwave sensor network and radar for improved rainfall measurement and mapping

Abstract. One of the main challenges for meteorological and hydrological modelling is accurate rainfall measurement and mapping across time and space. To date, the most effective methods for large-scale rainfall estimates are radar, satellites, and, more recently, received signal level (RSL) measurements derived from commercial microwave networks (CMNs). While these methods provide improved spatial resolution over traditional rain gauges, they have their limitations as well. For example, wireless CMNs, which are comprised of microwave links (ML), are dependant upon existing infrastructure and the ML' arbitrary distribution in space. Radar, on the other hand, is known in its limitation for accurately estimating rainfall in urban regions, clutter areas and distant locations. In this paper the pros and cons of the radar and ML methods are considered in order to develop a new algorithm for improving rainfall measurement and mapping, which is based on data fusion of the different sources. The integration is based on an optimal weighted average of the two data sets, taking into account location, number of links, rainfall intensity and time step. Our results indicate that, by using the proposed new method, we not only generate more accurate 2-D rainfall reconstructions, compared with actual rain intensities in space, but also the reconstructed maps are extended to the maximum coverage area. By inspecting three significant rain events, we show that our method outperforms CMNs or the radar alone in rain rate estimation, almost uniformly, both for instantaneous spatial measurements, as well as in calculating total accumulated rainfall. These new improved 2-D rainfall maps, as well as the accurate rainfall measurements over large areas at sub-hourly timescales, will allow for improved understanding, initialization, and calibration of hydrological and meteorological models mainly necessary for water resource management and planning.

Mechanical properties of structural bamboo following immersion in water

Bamboo is widely used as scaffolding for which collapses, often associated with rain events, are not uncommon. The presented study quantifies the degradation of mechanical properties of bamboo samples following immersion in water for 1 and 7days to simulate the effects of significant rain events. Compression, longitudinal shear and splitting tests were conducted to obtain the respective strengths and moduli. The mechanical properties were observed to degrade significantly with increased moisture content (MC) up to about MC=30%, a value close to the expected fiber saturation point (FSP). Beyond MC=30%, further degradation, while apparent, was less significant. Immersion in water for one day was observed to be sufficient to achieve the FSP; under these conditions, compressive strength was observed to be 75% of that obtained from tests conducted at a standard ‘air-dry’ MC=12%. Accompanying the reduction in strength with increased MC, the bamboo was observed to transition from a relatively brittle behavior to a very ductile behavior. For scaffold applications, degradation of compression capacity is not only critical but also shown to be a conservative indicator for other mechanical properties.

Geostatistical radar–raingauge merging: A novel method for the quantification of rain estimation accuracy

Compared to other estimation techniques, one advantage of geostatistical techniques is that they provide an index of the estimation accuracy of the variable of interest with the kriging estimation standard deviation (ESD). In the context of radar–raingauge quantitative precipitation estimation (QPE), we address in this article the question of how the kriging ESD can be transformed into a local spread of error by using the dependency of radar errors to the rain amount analyzed in previous work. The proposed approach is implemented for the most significant rain events observed in 2008 in the Cévennes-Vivarais region, France, by considering both the kriging with external drift (KED) and the ordinary kriging (OK) methods. A two-step procedure is implemented for estimating the rain estimation accuracy: (i) first kriging normalized ESDs are computed by using normalized variograms (sill equal to 1) to account for the observation system configuration and the spatial structure of the variable of interest (rainfall amount, residuals to the drift); (ii) based on the assumption of a linear relationship between the standard deviation and the mean of the variable of interest, a denormalization of the kriging ESDs is performed globally for a given rain event by using a cross-validation procedure. Despite the fact that the KED normalized ESDs are usually greater than the OK ones (due to an additional constraint in the kriging system and a weaker spatial structure of the residuals to the drift), the KED denormalized ESDs are generally smaller the OK ones, a result consistent with the better performance observed for the KED technique. The evolution of the mean and the standard deviation of the rainfall-scaled ESDs over a range of spatial (5–300km2) and temporal (1–6h) scales demonstrates that there is clear added value of the radar with respect to the raingauge network for the shortest scales, which are those of interest for flash-flood prediction in the considered region.

Evaluation of Precipitation Simulated by Seven SCMs against the ARM Observations at the SGP Site*

Abstract This study evaluates the performances of seven single-column models (SCMs) by comparing simulated surface precipitation with observations at the Atmospheric Radiation Measurement Program Southern Great Plains (SGP) site from January 1999 to December 2001. Results show that although most SCMs can reproduce the observed precipitation reasonably well, there are significant and interesting differences in their details. In the cold season, the model–observation differences in the frequency and mean intensity of rain events tend to compensate each other for most SCMs. In the warm season, most SCMs produce more rain events in daytime than in nighttime, whereas the observations have more rain events in nighttime. The mean intensities of rain events in these SCMs are much stronger in daytime, but weaker in nighttime, than the observations. The higher frequency of rain events during warm-season daytime in most SCMs is related to the fact that most SCMs produce a spurious precipitation peak around the regime of weak vertical motions but rich in moisture content. The models also show distinct biases between nighttime and daytime in simulating significant rain events. In nighttime, all the SCMs have a lower frequency of moderate-to-strong rain events than the observations for both seasons. In daytime, most SCMs have a higher frequency of moderate-to-strong rain events than the observations, especially in the warm season. Further analysis reveals distinct meteorological backgrounds for large underestimation and overestimation events. The former occur in the strong ascending regimes with negative low-level horizontal heat and moisture advection, whereas the latter occur in the weak or moderate ascending regimes with positive low-level horizontal heat and moisture advection.

Evaluation of erosion control geotextiles on steep slopes. Part 1: Effects on runoff and soil loss

Geotextiles have been demonstrated to be effective in reducing erosion and subsequent slope degradation processes. However, most studies devoted to assessing the effectiveness of those elements have considered small or intermediate slope gradients (normally ≤30°), whereas real engineering works often lead to steeper slopes needing protection. In addition, although a large amount of laboratory studies exist on this topic, there are few articles reporting field experiments which consider large plots, real precipitation and prolonged study periods. This paper is the first of two in which the performance of erosion control geotextiles on steep slopes (45° and 60°) has been assessed. In this paper, the influence of geotextiles on runoff and soil loss reduction was evaluated. The second paper focuses on the effects of geotextiles on the establishment and growth of vegetation on the slope. The research was carried out on an experimental embankment built in Pamplona (Spain) following standard construction procedures in order to resemble real engineering slopes. Two biological geotextiles (jute net and coir blanket) and a synthetic polyester geogrid, installed in two positions (surface-laid and buried), were evaluated and compared with a vegetated hydroseeded control plot. After each significant rain event, runoff and soil loss amounts produced on each plot were recorded. The results showed that coir and jute geotextiles produced 2–3 times larger runoff volumes than the control plots on both the 45° and 60° slopes, whereas the synthetic geogrid did not give significantly different runoff rates from the control (at p<0.05). Geotextiles were more effective in reducing soil loss at 45° than at 60°. The most effective treatment was the surface-laid geogrid, with a median Soil Loss Reduction Effectiveness (SLRE) of 76% and 53% for the 45° and the 60° slopes, respectively. At 45° the coir blanket showed lower soil losses than the control (median SLRE of 61%), but at 60° its protection action was more irregular (median SLRE of only 8%). The jute net and the buried geogrid produced lower erosion rates (median soil loss of 3.2gm−2 and 2.1gm−2, respectively) than the control (median soil loss of 3.6gm−2) at 45°, but at 60° the erosion rates observed were similar to those of the control. In short, the surface-laid geogrid produced the lowest soil loss rates. However, when buried, the geogrid did not effectively control erosion, at least not that of the upper soil layer. Thus, its surface installation seems to be a better option. In cases where burial is preferred for aesthetic reasons (i.e. hiding the geogrid), a higher soil loss must be assumed.

Water table, drainage, and yield response to drainage water management in southeast Iowa

Subsurface drainage is an important practice for optimizing crop production, but it accelerates nitrate-nitrogen (NO3-N) loss to downstream water bodies. As a result, there is a need for practices that can maintain crop production while decreasing subsurface drainage volume and NO3-N export. The objectives of this work were to evaluate the impact of drainage water management through controlled drainage, shallow drainage, conventional drainage, and no drainage on subsurface drainage volumes, water table depths, crop yields, and NO3-N export. This research was conducted at the Iowa State University Southeast Research Farm and consisted of four management schemes with two replicates for a total of eight plots. Plots consisted of a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation with half of the plot planted in corn and half planted in soybeans each year. Findings from four years show that undrained plots had a high occurrence of elevated water tables. Controlled and shallow plots had elevated water tables in the early spring and early fall in accordance with the rainfall and management protocols for controlled drainage. Water table response was quick, with drawdown to tile depth within one to two days after significant rain events. During the period of the study, drainage water management through controlled drainage or shallow drainage reduced overall drainage volume by 37% and 46%, respectively. Average annual NO3-N loss for the study period was reduced by 36% and 29% for controlled drainage and shallow drainage, respectively. Over the four-year period, corn yields in the controlled plots were significantly lower than conventional drainage; however, yields were not statistically different from shallow drained plots. There was no statistically significant difference between drained plots in terms of soybean yield for the study period. Undrained plots, however, had significantly lower yields for corn when compared with shallow and conventional treatments and for soybeans when compared to all treatments. This study highlighted the potential for use of drainage water management practices in reducing subsurface drainage volume and downstream NO3-N loss. In addition, the study highlighted the overall importance of drainage on maintaining crop yields.

Tests for field mould and associated mycotoxins in South Australian lentil (Lens culinaris) grain

Rain events in South Australia during the lentil harvest of 2010/2011 raised concerns as to whether grain had been infected with field moulds and associated mycotoxins. Grain samples from commercial crops were tested for the mycotoxins Deoxynivalenol (DON = Vomitoxin), Fumonisin B1 and B2 and zearalenone, which are produced by Fusarium spp. Sampling was biased towards more severely affected grain to increase the probability of detection of moulds and toxins, including worst case samples of discarded waste grain (screenings) from cleaning plants. No mycotoxins were detected although Fusarium spp. were detected in all but three of the samples. No Alternaria or Aspergillus spp. were detected. Fusarium spp. were detected at a higher level in grain harvested after a significant rain event in December 2010 compared to grain harvested prior to this event. Percentage of stained seed was higher in plants sampled in machinery wheel tracks compared to those from the remainder of the paddock. The fungal pathogen Ascochyta lentis was also detected on the grain but percentage infection was not affected by harvest date. No Botrytis spp. were detected on the samples. The pilot study identified that the lentil grain in these samples from the 2010/2011 harvest in South Australia was free of mycotoxins and posed no risk to humans or livestock.