Increasing Rain Intensity Research Articles

Rainfall Runoff and Nitrogen Loss Characteristics on the Miyun Reservoir Slope

Rainfall intensity and slope gradient are the main drivers of slope surface runoff and nitrogen loss. To explore the distribution of rainfall runoff and nitrogen loss on the Miyun Reservoir slopes, we used artificial indoor simulated rainfall experiments to determine the distribution characteristics and nitrogen migration paths of surface and subsurface runoff under different rainfall intensities and slope gradients. The initial runoff generation time of subsurface runoff lagged that of surface runoff, and the lag time under different rainfall intensity and slope conditions ranges from 3.97 to 12.62 min. Surface runoff rate increased with increasing rainfall intensity and slope gradient; compared with a rainfall intensity of 40 mm/h, at a slope of 15°, average surface runoff rate at 60 and 80 mm/h increased by 2.38 and 3.60 times, respectively. Meanwhile, the subsurface runoff rate trended upwards with increasing rainfall intensity, in the order 5 > 15 > 10°. It initially increased and then decreased with increasing slope gradient, in the order 5 > 10 > 15°. Total nitrogen (TN) loss concentration of surface runoff shows a decrease followed by a stabilization trend; the concentration of TN loss decreases with decreasing rainfall intensity, and the stabilization time becomes earlier and is most obvious in 5° slope conditions. TN loss concentration in subsurface runoff decreased with increasing rainfall intensity, i.e., 40 > 60 > 80 mm/h. The surface runoff rainfall coefficient was mainly affected by rainfall intensity, a correlation between αs and slope gradients S was not obvious, and the fitting effect was poor. The subsurface runoff rainfall coefficient was mainly affected by slope gradient, the R2 of all rainfall intensities was <0.60, and the fitting effect was poor. The main runoff loss pathway from the Miyun Reservoir slopes was surface runoff, which was more than 62.57%. At the same time, nitrogen loss was subsurface runoff, more than 51.14%. The proportion of surface runoff to total runoff increases with the increase of rainfall intensity and slope, with a minimum of 62.57%, and the proportion of nitrogen loss from subsurface runoff also decreases with increasing rainfall intensity but does not change with slope gradient. The order of different runoff modulus types was mixed runoff (surface and subsurface runoff occur simultaneously) > surface runoff > subsurface runoff. The surface and mixed runoff modulus increased significantly with increasing rain intensity under different rain intensities and slope gradients. Overall, rainfall intensity significantly affected slope surface runoff, and slope gradient significantly affected nitrogen loss.

ОЦЕНКА НЕСУЩЕЙ СПОСОБНОСТИ ПОЧВЫ ПРИ ПОЛИВЕ ДМ «КУБАНЬ-ЛК1» УЧАСТКОВ НА СЛОЖНОМ РЕЛЬЕФЕ

The issues of ensuring sufficient support-coupling properties of the Kuban-LK1 widesprinkler sprinkling machine (SM) for working on difficult terrain areas by increasing the bearing capacity of the soil surface are considered. It is noted that with increased rain intensity and, accordingly, increased puddle formation in the zone of movement of running systems, intensive rutting is observed, leading to a bend in the water supply pipeline and, ultimately, to the operation of the protection system. This drawback has a negative impact on the shift time utilization rate and, consequently, on the overall performance of the SM. A progressive decrease in the intensity of the SM water supply is proposed to be used to eliminate it, which will lead to an increase in the bearing properties of the soil. It was determined that when working on slopes, the rain intensity at the end of the SM is 0.4 mm/min. It has been experimentally established that a decrease in the intensity of rain can be achieved by reducing the consumption of sprinklers, as well as by increasing the spray area of the jet. Installation of control devices is proposed to reduce the intensity to 0.3 mm/min. But it has been established that further regulation of rain intensity values is limited by the maximum allowable length of the decrease in the irrigation radius by sprinklers. The installation of stubble-type spreaders for spraying the jet of sprinklers is proposed to reduce the intensity of rain to 0.2 mm/min. An analysis of the experimental data on the dependence of the soil bearing capacity on the intensity of rain and the magnitude of surface runoff showed that with a progressive decrease in the intensity of rain, control devices and dividers provide an increase in the bearing capacity of the soil from 43–47 kPa without control devices to 72–82 kPa with them. Ultimately, the provision of sufficient support properties makes it possible to achieve productive operation of the Kuban-LK1 DM on slope areas.

ПОВЫШЕНИЕ ОПОРНЫХ СВОЙСТВ МНОГООПОРНОЙ МАШИНЫ «КУБАНЬ-ЛК1»

Considered Issues of increasing the reliability of the movement of the sprinkling machine (SM) on the example of "Kuban-LK1" were considered. Significant rutting leading to loss of patency due to increased rain intensity at the end of the SM (last bogies and cantilever) was noted, which ultimately leads to a decrease in machine performance. To eliminate this drawback, pneumatic tires with a profile width of 21.3 - 24 are installed on the outermost SM bogie, the rain intensity of which is 1.0 mm / min, and the length is 350 - 400 m, instead of serial tires 18.4 - 24. To eliminate this shortcoming, pneumatic tires with a profile width of 21.3 - 24 are installed on the extreme SM trolley, the rain intensity of which is 1.0 mm / min, and the length is 350 - 400 m, instead of serial tires 18.4 - 24. Modifications of SM with a length of 500 meters or more characterize increased intensity (ρ = 1.0-1.2 mm/min), and, accordingly, an increased value of surface water runoff, while the bearing capacity of the soil in the area of the last spans is up to 70 kPa. This determines the need to install wide-profile pneumatic tires with a profile width of 21.3 - 24 not on one, but on several last bogies. However, based on the high cost and weight indicators of pneumatic tires 21.3 - 24, according to theoretical and experimental studies, the authors recommend equipping the last SM bogies with pneumatic tires of a conventional profile 18.3 - 24 with a rigid flare, the radius of which is determined by reducing the wheel radius by an amount equal to the average depth of immersion of tires of a conventional profile, at the end of the irrigation season. The conducted experimental studies have shown that the installation of an expander on the pneumatic tires of the last bogies provided the indicators of the reference rutting ability, equivalent to those of the intermediate bogies.

Development and Implementation of a Prototype Automatic Rain-Sensor Car Wiper System

Various studies have been conducted over the years on how to reduce driver distractions while driving, but with little effort on the distraction that could be caused by manually operated wipers while driving whenever it rains. Drivers frequently take their hands off the steering to turn ON/OFF and adjust the wiper speed when driving during rain, which causes a loss of concentration and increases the risk of a car accident. This paper presents an automatic car wiper prototype system that adjusts the speed of the wiper based on the intensity of the rain. The system also includes an audio alert that warns the driver to stop driving during heavy rain. The rain sensor/intensity and servo motor; which regulates the wiper's speed, were interfaced by an ATMega328 (Arduino Uno A000066). It performed satisfactorily, with average response times of 0.78 seconds, 1.95 seconds, and 6 seconds for rain water detection, increasing rain intensity, and no rain detection respectively. The wiper speed was 15 rpm at moderate rain intensity and 32 rpm at heavy rain intensity. The wiper average response time and speed shows that it is a system that eliminate delay as compare to manually operated car wiper system. The developed system will reduce driver distractions while driving thereby reduces the risk of a car accident. As a result, this system can be combined with new technologies seen in contemporary vehicles.

PENGARUH INTENSITAS HUJAN DAN PENUTUP LAHAN (LAND COVER) TERHADAP NILAI KOEFISIEN ALIRAN PERMUKAAN (C) MENGGUNAKAN RAINFALL SIMULATOR

The influence of land cover and intensity is one of the factors that influence the value of surface flow coefficient (C). The coefficient value will affect the surface flow occurs during peak discharge. In this research, calculate surface coefficient (C) with variation intensity 40 mm/h, 50 mm/h, 60 mm/h, 70 mm/h for land cover paving block (brick pattern and matting pattern), grass block , mini elephant grass, sand and concrete pavement. This test is expected to be the solution in choosing the right type of land cover as a substitute for concrete pavement in the parking lot, park, or home or office yard. The implementation methodology was carried out by laboratory testing with rainfall simulator, 4 cm high base layer of sand and various land cover around 4 cm. The test that carried out in this study include filter analysis, rain intensity and surface coefficient value (C) testing. Testing value of coefficient including the test using rational formulas and testing by definition (Scwab, 1981 and Mc Guen, 1989). The result of this research obtained coefficient of land cover paving block pattern of stacking brick 0,857-0,891, in land cover paving block matting pattern 0,825-0,856, while at grass block 0,677-0,765. The coefficient of surface flow (C) for concrete pavement cover is 0.961-0,997, mini elephant grass cover is 0,483-0,538, while without land cover is 0,559-0,639. The value of surface flow coefficient (C) is getting bigger with increased rain intensity and land cover that has fewer gaps, in this case there is a significant difference in the paving block and grass block.

Effects of rain intensity, slope gradient and particle size distribution on the relative contributions of splash and wash loads to rain-induced erosion

Soil erosion during rainfall is a complex phenomenon resulting from detachment by raindrop impact and overland flow. The objective of this study is to investigate the transportation rate of splash load (SL) and that of wash load (WL) and their relative contributions to the rain-induced erosion rate affected by rain intensity, slope gradient and particle size distribution. A total of 60 simulation runs were carried out using a detachment tray under simulated rainfall with no inflow. The experiments were done on two soil samples (aggregate sizes finer than 2 and 4.75mm) from an agricultural land use at different rain intensities (57 and 80mmh−1) and varying slope gradients (0.5%, 2.5%, 5%, 10%, and 20%). Under unsteady state conditions, WL showed relatively high dependency on slope gradient, whereas approaching steady state conditions, nearly similar values of WL occurred at different slopes. SL and WL increased with increasing rain intensity and slope gradient, implying the importance of rain-induced erosion on bare agriculture lands especially at steeper slopes. The ratio of WL/SL decreased when slope gradient increased; however, WL increased more significantly than SL as soil aggregates became finer. The result indicates that at all the slope gradients, WL was much larger than SL, indicating that wash load significantly contributes to the rain-induced erosion in the agricultural soil. Furthermore, with increasing slope gradient, the contribution of wash load to rain-induced erosion decreased, while it was greater in the soil containing finer aggregates. Also, with increasing rain intensity at lower slope gradients (<10%), further increase in splashed materials than that in washed materials occurred, whereas the reverse order was found at steeper slopes (>10%). The finding of this study revealed that the rain-induced erosion was transport-limited at the gentler slopes, whereas at the steeper slopes, it shifted to detachment-limited conditions.

Changed surface roughness by wind erosion accelerates water erosion

Wind and water erosion are two dominant types of erosion that lead to losses of soil and water; understanding their interactions is important for estimating soil quality and environmental impacts in regions where both types of erosion occur. This study was devoted to investigate the characteristics of the surface roughness, runoff, and erosion rates under a one-way wind erosion-rain erosion sequence. The experimental setup included a wind tunnel and a rain simulator. Soil samples were collected from a sloped wasteland in Wuqi County, northern Shaanxi province, China. This experiment was conducted with wind erosion firstly and water erosion thereafter, with three wind speeds (0 [control], 11, and 14 m s−1) and rain intensities (60, 80, and 100 mm h−1). The physical properties of top soil samples (0–1 cm) were analyzed after each wind erosion test. The soil surface roughness (mm), runoff (mm h−1), and erosion (g m−2 h−1) rates were calculated after wind and water erosion. Linear regression analysis was used to estimate the relationships between surface roughness, runoff rate, erosion rate, and erosion factors. Wind erosion increased the sand content in the top 1 cm of soil in simulation area by 6.51–6.74 % and decreased clay and silt contents by 7.65–9.15 and 17.94–18.15 %, respectively, relative to the original surface soil. Compared with the control, the wind erosion treatments increased the surface roughness, runoff, and erosion rates by 8.12–78.06, 4.5–21.69, and 7.25–38.97 %, respectively, at wind speeds of 11 and 14 m s−1. The relationship between runoff and rain duration under different rain intensities after wind erosion were described well by a logarithmic function, whereas a large degree of variation was observed in erosion rate. The increased values of runoff and erosion rates in the different treatments, however, became weaker with increasing rain intensity, probably due to the much higher energy of the rain at the highest intensity, which decreased the proportional influence of wind erosion on the microtopography of the soil. Linear regression showed that surface roughness, runoff, and erosion rates were positively associated with wind speed and rain intensity (P < 0.01). Wind erosion clearly has the capacity to intensify water erosion. Results demonstrate the need for controlling of wind erosion to reduce water erosion in regions where both types of erosion occur. Moreover, a consideration of the impact of wind erosion on water erosion is required for effective erosion prediction in these regions.

Exploring changes in rainfall intensity and seasonal variability in the Southeastern U.S.: Stakeholder engagement, observations, and adaptation

The distribution of rainfall has major impacts in agriculture, affecting the soil, hydrology, and plant health in agricultural systems. The goal of this study was to test for recent changes in rainfall intensity and seasonal rainfall variability in the Southeastern U.S. by exploring the data collaboratively with agricultural stakeholders. Daily rainfall records from the Global Historical Climatology Network were used to analyze changes in rain intensity and seasonal rainfall variability. During the last 30years (1985–2014), there has been a significant change (53% increase) in the number of extreme rainfall days (>152.4mm/day) and there have been significant decreases in the number of moderate intensity (12.7–25.4mm/day) and heavy (25.4–76.2mm/day) rainfall days in the Southeastern U.S., when compared to the previous 30-year period (1955–1984). There have also been significant decreases in the return period of months in which greater than half of the monthly total rain occurred in a single day; this is an original, stakeholder-developed rainfall intensity metric. The variability in spring and summer rainfall increased during the last 30years, but winter and fall showed less variability in seasonal totals in the last 30years. In agricultural systems, rainfall is one of the leading factors affecting yield variability; so it can be expected that more variable rainfall and more intense rain events could bring new challenges to agricultural production. However, these changes can also present opportunities for producers who are taking measures to adjust management strategies to make their systems more resilient to increased rain intensity and variability.

Effects of Rain on Traffic Operations on Florida Freeways

Although the correlation between traffic variables and weather appears to be intuitive, quantifying the effects that weather, especially rain, has on driver response in travel speeds and traffic demands is needed to evaluate practical aspects of traffic operations. Previous studies have researched driver responses to inclement weather on freeways located in northern regions of the United States and Canada. However, driver familiarity with local weather conditions is a factor that should be considered in determining inclement weather effects on traffic variables. The focus of this research was to examine driver response to rain precipitation on freeways located in the southeastern regions of the United States to determine whether results from previous studies were general indicators or location specific in nature. To study the impacts of rain precipitation on hourly mean speeds and traffic volumes, hourly weather data and traffic sensor data were collected for two freeway segments in Jacksonville, Florida. The study investigated conditions such as wet versus dry (rain or no rain) and dry versus rain intensity (no rain or light, moderate, or heavy rain) for each segment. The results indicated that mean travel speeds decreased during rainfall events and speed reductions increased with increasing rain intensity. Reductions found for light rainfall events were within the range of previous studies; however, speed reductions during moderate to heavy rains varied widely. The results also indicated that the hour of the day was a factor in the degree of motorists’ speed reduction. Traffic volumes also declined during rainy conditions, with significant reductions during peak hours.

Aeration tank settling and real time control as a tool to improve the hydraulic capacity and treatment efficiency during wet weather: results from 7 years' full-scale operational data

This paper investigates the aeration tank settling (ATS) operation in combination with real time control (RTC) as a tool for increasing the hydraulic capacity and improving the treatment efficiency of a wastewater treatment plant (WWTP) during wet weather flows. Results from 7 years' full-scale operational data at the Avedøre WWTP, Denmark, show that ATS operation in combination with RTC increases the hydraulic capacity of the treatment plant with up to 150 and 67% of the design capacity during winter and summer respectively. Compared to the conventional wet weather operation, the ATS in combination with RTC operation resulted in lower effluent concentrations for total phosphate (40-50%), suspended solids (30-60%) and chemical oxygen demand (30-50%), whereas no significant effect was observed on total nitrogen. Apart from the reduced effluent concentrations, the RTC resulted in economic savings in the form of reduced costs for electricity and green taxes. However, in very few cases the ATS operation in combination with RTC was not able to handle design capacity, and some overflows occurred at flows below the design capacity. The frequency of these overflows may increase in the future due to increased rain intensity resulting in shorter prediction time available for ATS.

Precipitation Contribution of Tropical Cyclones in the Southeastern United States from 1998 to 2009 Using TRMM Satellite Data

Abstract The objective of this paper is to characterize the precipitation amounts originating from tropical cyclones (TCs) in the southeastern United States during the tropical storm season from June to November. Using 12 years of precipitation data from the Tropical Rainfall Measurement Mission (TRMM), the authors estimate the TC contribution on the seasonal, interannual, and monthly precipitation budget using TC information derived from the International Best Track Archive for Climate Stewardship (IBTrACS). Results derived from the TRMM Multisatellite Precipitation Analysis (TMPA) 3B42 showed that TCs accounted for about 7% of the seasonal precipitation total from 1998 to 2009. Rainfall attributable to TCs was found to contribute as much as 8%–12% for inland areas located between 150 and 300 km from the coast and up to 15%–20% for coastal areas from Louisiana to the Florida Panhandle, southern Florida, and coastal Carolinas. The interannual contribution varied from 1.3% to 13.8% for the period 1998–2009 and depended on the TC seasonal activity, TC intensity, and TC paths as they traveled inland. For TCs making landfall, the rainfall contribution could be locally above 40% and, on a monthly basis, TCs contributed as much as 20% of September rainfall. The probability density functions of rainfall attributable to tropical cyclones showed that the percentage of rainfall associated with TC over land increased with increasing rain intensity and represent about 20% of heavy rainfall (&amp;gt;20 mm h−1), while TCs account for less than 5% of all seasonal precipitation events.

Acid rain and particulate matter dynamics in a mid-sized Andean city: The effect of rain intensity on ion scavenging

Acid rain phenomenon (average WVM pH = 4.9) and a strong association of sulfate scavenging and rain intensity (R2 = 0.8118) were observed over a seven-month period (October 2010–April 2011) at a densely populated mid-sized Andean city (pop 380,000) that occupies mountain ridge topography (2150 m.a.s.l.). Rain chemistry and PM10 were fairly consistent over four sampling sites representing various scenarios of urban density and topography. All stations exhibited differences in the sulfate content in PM10 between dry and wet periods, further illustrating the sulfate scavenging dynamic. Concentration of major ions evaluated in rain were in order of sulfates (35.2–53.5 μeq L−1) > calcium (14.6–17.3 μeq L−1) > chlorides (3.5–5.1 μeq L−1) > nitrates (2.1–3.1 μeq L−1). Major chemical constituents of PM10 were related with ionic composition of rainwater through scavenging ratios (SRs). High sulfate SRs associated with increased rain intensity reflected higher sulfate ion solubility. Significant contribution of sulfates to total ionic content, higher than 50% at all monitoring stations, suggests important contributions of SO2 emissions, which could come from three principal sources: vehicular emissions due to Colombian fuels with elevated sulfur content, industrial emissions at southeast of the city, and sulfur gas emissions from a nearby active volcano, Nevado del Ruiz, located 27 km southeast of the city.

Increased rainfall remarkably freshens estuarine and coastal waters on the Pacific coast of Panama: Magnitude and likely effects on upwelling and nutrient supply

Increased intensity of rainfall events during late 2010 led to a remarkable freshening of estuarine, near- and off-shore waters in coastal Pacific Panama. The increased rain intensity during the wet season of 2010 lowered salinity of estuarine and coastal waters to levels unprecedented in previous years. Fresher conditions were most marked within estuaries, but even at 6km from shore, salinities were 8–13‰ lower during the 2010 wet season, compared to a lowering of up to 2‰ during previous wet seasons. Freshwater added to surface waters by rain had major biological, hydrodynamic, and biogeochemical consequences, increasing stream erosion, uprooting stream-edge terrestrial and mangrove trees, increasing mortality of benthic fauna, damping upwelling of denser, nutrient-rich water that was expected given the contemporaneous most intense La Niña in decades, as well as by enriching surface seawater by direct deposition and by horizontal advection of nutrients from land. It appears that wet season rainfall is slowly increasing in the region, and if the level of rainfall reported here is a harbinger of future climate change effects on land–sea couplings in tropical coastal ecosystems, the resulting freshening could significantly shift biogeochemistry and coastal food webs in the region and elsewhere.

祁连山典型灌丛降雨截留特征

Rainfall intercepting by vegetation plays an important role affecting the water balance at local and catchment scale due to the control that vegetation canopy exert by modifying both evaporation and the redistribution of incident rainfall.Qilian Mountain is source regions of Heihe River,Shiyang River and Shule River inland river basin.In consideration of widespread shrubs which account for 68% of the whole forest area of Qilian Mountain,the research on rainfall interception process of shrubs for understanding the impact of rainfall characteristics on alpine shrubs and revealing the mechanism of hydrologic cycle and water resources with the impact of the shrub canopy,especially in the mountainous regions of an inland river basin,is very important and necessary.This paper taked the four typical alpine shrubs Potentilla fruticosa,Salix cupularis,Hippophae rhamnoides,and Caragana jubata in Qilian Mountain as test objects,based on the field experimental data from June to October 2010,characteristics of rainfall interception and rainfall redistribution of four typical alpine shrubs in Qilian Mountain was investigated by permanent plot method,and impact of rainfall characteristics on rainfall redistribution of shrubs was analyzed by statistical method.The results indicated that the gross rainfall was 298.6 mm during the experimental period.Rainfall was intercepted entirely by shrubs when rainfall is less than 2.1 mm,gross rainfall which observed throughfall and stemflow was 283.1 mm.The amount of throughfall of P.fruticosa,S.cupularis,H.rhamnoides and C.jubata was 175.8 mm,179.8 mm,148.1mm,and 170.4 mm.Throughfall percentages of P.fruticosa,S.cupularis,H.rhamnoides and C.jubata was 62.0%,63.5% 52.3%,and 60.2%,respectively.Stemflow was 9.5 mm,9.1 mm,22.5 mm,and 11.8 mm for P.fruticosa,S.cupularis,H.rhamnoides,and C.jubata,and averaged 3.4%,3.2%,8.0%,and 4.2% of the gross rainfall,respectively.Interception was 62.0 mm,63.5 mm,52.3 mm,and 60.2 mm for P.fruticosa,S.cupularis,H.rhamnoides,and C.jubata,and accounted for 34.6%,33.3%,39.7%,and 35.6% of the gross rainfall,respectively.The amount of thoughfall,stemflow and interception of P.fruticosa,S.cupularis,H.rhamnoides and C.jubata increased in a significant positive linear correlation with increasing rainfall depth(P0.001).The relationship of throughfall percentage,stemflow percentage and interception percentage of shrubs with rainfall could be fitted with exponential curve(P0.05).Throughfall percentage and stemflow percentage showed an increase trend with the increasing rainfall,while interception percentage decreased with the increasing rainfall depth.Moreover,interception percentage of shrubs decreased in exponential function correlation with increasing rain intensity(P0.05).Interception percentage decreased with increasing rainfall intensity,when the rainfall intensity is less than 4 mm/h,the interception percentage was significantly decreased,and then the trend is becoming stable values with increasing rainfall intensity.Interception characteristics of each shrubs was different with others when rainfall characteristics were similar during the experimental period.According to field plot observation,the height,branch angle,canopy morphology and crown projection area all affected canopy interception process of alpine shrubs in Qilian Mountain.In order to analyze intercept capability per leaf area of shrubs,some morphology characteristics parameters,such as leaf area index(LAI),freedom throughfall coefficient,biomass,canopy hold water ability,should be measurement in the next experiment.

Increasing rain intensity over Okinawa, 1982–2005, and the link to changes in characteristics of northwest Pacific typhoons

Daily rainfall variation over the strategically situated western Pacific island of Okinawa is investigated for 1982–2005. Although no trend in the annual rainfall was observed, analyses using a probability distribution function for each year revealed that the frequency of light (0–3 mm d−1) and heavy (26–50 mm d−1) rainfall events have a statistically significant decreasing trend, while extreme (&gt;75 mm d−1) rainfall events have been increasing. Such events are associated with typhoons. An analysis of typhoons passing near Okinawa during 1982–2005 revealed that a cause of the increasing trend in heavy rainfall was increased rainfall amounts per typhoon rather than a rising number of strong typhoons approaching the island. In particular, typhoons which passed to the west of Okinawa, or which approached the island within 100 km, during the peak typhoon month of September showed a statistically significant increase in total rainfall of 6.5 mm y−1 over this time period. This is partially due to a slowing of the typhoon speeds in the latter half of the record. This work supports other recent studies that suggest changes to characteristics of stronger tropical storms are not restricted to the North Atlantic although, owing to the limited length of the record, we are not able to determine at this time whether the observed trends are unusual compared with natural multidecadal variability.

Analysis of Short Space–Time-Scale Variability of Oceanic Rain Using TOPEX/Jason

Abstract Information on the spatial and temporal variability of rain rate is important not only for meteorology and hydrology but also for the design of remote sensing and in situ measuring or of millimeter wave communication systems. The Ocean Topography Experiment (TOPEX)/Jason Tandem Mission (TM) collocated rain dataset is used in this study to determine the small space-scale (5 km) and time-scale (70 s) rain variability. TOPEX and Jason dual-frequency (Ku and C bands) radar altimeter data have been extensively used during the past decade to detect and study oceanic precipitations. During the TM, designed to intercalibrate and validate the two altimeters, the two satellites were put on the same orbit with a 70-s time separation. With combined use of altimeter and passive microwave radiometers (also available on board altimeter missions), rain intensity, rain attenuation, rain layer height, rain event length, and surface winds can also be estimated and provide valuable coincident geophysical contextual information. The size of the TM collocated rain database (140 000 samples) is large enough to allow a meaningful statistical analysis of the time–space variability of rain over the World Ocean. The analysis of the different terms contributing to the variability of rain attenuation, from which rain rate is inferred, shows that the geophysical and/or instrumental noise is small enough to allow a meaningful estimation of the variability of the measured rain rate. The analysis of the time and space variabilities and their relation reveals two well-defined regimes. The first one, corresponding to convective rain cells (i.e., rain rate greater than 3–4 mm h−1, length smaller than 50 km, and freezing level greater than 3.5 km), is characterized by high temporal and spatial variabilities (greater than 2–3 mm h−1) that increase with increasing rain intensity and decreasing cell length. Horizontal variability is significantly larger than the temporal one and surface wind has a very limited impact. The second regime corresponds to stratiform and/or weak rain cells. The temporal and spatial variabilities are relatively low (on the order of 1–2 mm h−1) and vary little with rain intensity and cell length. The temporal variability increases with surface wind and largely exceeds the spatial variability (ratio of 2 or more); the ratio strongly increases with increasing wind speed.

Monitoring rainfall trends to predict adverse impacts—a case study from Sri Lanka (1964–1993)

This paper describes an analysis of long-term rainfall trends in central mountainous region of Sri Lanka. A 30-year 60 rain gauge data set is analyzed to identify the trends in annual and seasonal rainfall. Inter-annual as well as intra-annual rainfall trends are investigated to understand the adverse impacts on water resources, floods and land degradation. It is found that there is a decrease in the annual rainfall in the region, while different seasons show mixed results. The March–April 1st inter-monsoon period shows the highest decrease in rainfall where almost all the rain gauges have recorded decreasing rainfall. In addition to the decreasing rainfall trend, the numbers of rainy days have reduced giving rise to an increasing rain intensity trend. In order to understand better the changes to rain intensity-frequency relation, a universal multifractal analysis was carried out where multifractal models calibrated to first and last decades of the rain series are used to estimate the intensity–frequency relations in the rainfall series. The results show that there is a decrease of inter-monsoon rainfall, while the intensities and return period of extreme events appear to become shorter. These changes could be associated with regional climate changes, and are consistent with projections related to Asia Brown Cloud phenomena.

Rainfall interception loss by pebble mulch in the semiarid region of China

Pebble mulches have been used to conserve soil moisture in the semiarid regions of China for over 300 years. However, little work has been carried out on rainfall interception loss by a pebble mulch layer. A field study was conducted to measure interception loss by pebble mulches during individual rainfall events, determine the rainfall-storage capacity of pebble mulch, and discuss the relationships between interception and rainfall parameters. The study showed that pebble size could affect interception loss. A 5 cm-thick pebble mulch layer, with pebbles 7.5–14.0 cm in the long dimension and 5.0–9.0 cm in the short dimension (larger pebble), had a saturation value of 0.281 mm, an average interception of 0.481 mm, and an average percentage interception of 11.5% during individual rainfall events. In contrast, a similar layer, with pebbles 2.0–6.5 cm in the long dimension and 2.0–6.0 cm in the short dimension (smaller pebble), had a saturation value of 0.526 mm, and an average interception of 0.742 mm, or 17.4% gross rainfall per storm. The correlation between interception by pebble mulch and gross rainfall was poor. The proportion of gross rainfall intercepted by pebble mulch tended to decrease as gross rainfall increased. The reduction in percentage was very marked for rains over 10 mm. Interception showed a tendency to decline with increasing rain intensity ( I 30). There was a broad variability in interception for intensities under 6 mm h −1. Interception tended to remain constant at about 0.25 mm for larger pebble and 0.40 mm for smaller pebble when intensity was over 6 mm h −1. Antecedent water content of pebble before a storm significantly affected interception loss, with about 50% interception occurring in the initial stage of a rainfall event. Rainfall duration and wind factors should, therefore, also be considered in future interception analysis.

Unsaturated zone processes and the hydrologic response of a steep, unchanneled catchment

As part of a larger, collaborative study, we conducted field experiments to investigate how rainfall signals propagate through an unsaturated soil profile, leading to a rapid pore pressure response and slope instability. We sprinkler‐irrigated an entire, unchanneled headwater basin in the steep, humid Oregon Coast Range, and we drove the system to quasi steady state as indicated by tensiometers, piezometers, and discharge. During initial wetting some of the deeper tensiometers responded before the arrival of an advancing head gradient front. With continued irrigation most tensiometers attained near‐zero pressure heads before most piezometers responded fully, and a stable unsaturated flow field preceded the development of a stable saturated flow field. Steady discharge occurred after the last piezometer reached steady state. With the onset of steady discharge the unsaturated zone, saturated zone, and discharge became delicately linked, and a spike increase in rain intensity led to a response in the saturated zone and discharge much faster than could have happened through advection alone. We propose that the rain spike produced a slight pressure wave that traveled relatively rapidly through the unsaturated zone, where it caused a large change in hydraulic conductivity and the rapid effusion of stored soil water. An important control on the hydrologic response of this catchment lies with the soil‐water retention curve. In general, below pressure heads of about −0.05 m, soil‐water contents change slightly with changes in pressure head, but above −0.05 m the soil‐water content is highly variable. Minor rainstorms upon a wet soil can produce slight changes in pressure head and corresponding large changes in soil‐water content, giving rise to the passage of pressure waves in response to increased rain intensity and a relatively rapid response in the unsaturated zone. This rapid unsaturated zone response led to a rapid rise in the saturated zone, and it may be the underlying mechanism enabling short bursts of rain to cause slope instability.

Contrasting behavior of gas and aerosol scavenging in convective rain: A numerical and experimental study in the African equatorial forest

A two‐dimensional convective cloud model has been coupled with a chemical model consisting of the explicit prediction of five chemical species: SO2, SO42−, NH4+, O3, and H2O2. The model takes the scavenging processes into account. We examine the relationship between the liquid water content (LWC) and the chemical concentrations of atmospheric trace elements in convective precipitation. The model results compare favorably with observations (ABLE 2B and DECAFE experiments). The modeled dilution curves were found to be nonlinear, in agreement with the DECAFE data. The model also accounts for the large differences in dilution effects that exist between gases and aerosols. More generally, this study shows that within the African equatorial forest there are (1) a reduction of aerosol scavenging efficiency with increasing rain intensity (or LWCg); (2) a strong impact of vertical profiles of atmospheric trace elements on ground rain concentrations; (3) a difference in scavenging efficiencies according to the origin of the elements (gas or aerosol) and (4) a depletion of atmospheric concentrations during rainfall.