Daily Rainfall Totals Research Articles

The PESERA coarse scale erosion model for Europe. I. – Model rationale and implementation

SummaryThe principles and theoretical background are presented for a new process‐based model (PESERA) that is designed to estimate long‐term average erosion rates at 1 km resolution and has, to date, been applied to most of Europe. The model is built around a partition of precipitation into components for overland flow (infiltration excess, saturation excess and snowmelt), evapo‐transpiration and changes in soil moisture storage. Transpiration is used to drive a generic plant growth model for biomass, constrained as necessary by land use decisions, primarily on a monthly time step. Leaf fall, with corrections for cropping, grazing, etc., also drives a simple model for soil organic matter. The runoff threshold for infiltration excess overland flow depends dynamically on vegetation cover, organic matter and soil properties, varying over the year. The distribution of daily rainfall totals has been fitted to a Gamma distribution for each month, and drives overland flow and sediment transport (proportional to the sum of overland flow squared) by summing over this distribution. Total erosion is driven by erodibility, derived from soil properties, squared overland flow discharge and gradient; it is assessed at the slope base to estimate total loss from the land, and delivered to stream channels.

The Impact of Trade Wind Strength on Precipitation over the Windward Side of the Island of Hawaii

Abstract The effects of trade wind strength and the diurnal heating cycle on the production of summer trade wind rainfall on the windward side of the island of Hawaii are examined from the data collected from the Hawaiian Rainband Project (HaRP) during 11 July–24 August 1990 and from National Weather Service Hydronet and National Climatic Data Center rain gauge data during 11 July–24 August for the years 1997–2000. For strong trades, the daily rainfall totals on the windward lowlands west of Hilo are higher with a nocturnal maximum there due to the convergence of the katabatic flow and the incoming decelerating trade wind flow, and orographic lifting aloft. The maximum rainfall axis shifts farther inland when trades are stronger. Except in the late afternoon hours, rainfall amounts on the windward side are higher when trades are stronger. For weak trades (≤5 m s−1), the rainfall distributions have a pronounced late afternoon maximum on the windward slopes due to the development of anabatic winds. The nocturnal rainfall over the windward lowlands and the early morning coastal rainfall are lower when trades are weaker.

Characterization of rain attenuation in Bangladesh and application to satellite link design

For a reliable quantification of rain attenuation in an Earth‐space link, determination of the temporal, year‐to‐year variation of rainfall is required as the distribution of rainfall is not uniform over the year. This paper discusses rainfall pattern, rain rate distribution, and rain attenuation characteristics in Bangladesh. Cumulative distribution of 1‐min rain rate is derived from 40 years of daily rainfall totals using the Rice‐Holmberg model. On the basis of these rain rates, rain attenuation at 18.7 GHz band is predicted by the International Telecommunication Union Radiocommunication Assembly (2003b). A reduction factor necessary to match similarly predicted rain attenuation with satellite beacon measurements at the same frequency in Sparsholt, United Kingdom, is modelled. This is applied to produce a novel rain attenuation prediction for Bangladesh where direct beacon measurements are not available. Inherent variability in this rain attenuation prediction is also quantified.

Characteristics of long‐duration precipitation events across the United States

Previous studies have indicated that extreme precipitation intensity is increasing over time, and has been attributed to anthropogenic warming. Generally these studies have limited analyses to data from daily rainfall totals. We extend those studies by examining characteristics associated with storms of varying duration. We find that significant differences exist in the character of long‐duration storms (those of twenty consecutive hours or more) from 1948 to 2004. Specifically we find that, although long‐duration storms are becoming wetter, (a) they are occurring less frequently and, consequently, comprising a progressively smaller proportion of the total storm number, and (b) they are contributing a smaller proportion of the total rainfall. Geographically, these storms are more likely to influence the Gulf States (particularly in autumn) and the central west coastal area of northern California. Fundamentally, this study suggests that evaluating precipitation over daily time frames may not capture the full complexities in extreme rainfall events.

Análise de distribuição de chuva para Santa Maria, RS

O estudo em pauta teve como objetivo analisar a distribuição da quantidade diária de precipitação e do número de dias com chuva e determinar a variação da probabilidade de ocorrência de precipitação diária, durante os meses do ano, em Santa Maria, RS. Os dados de precipitação utilizados foram obtidos durante 36 anos de observação, na Estação Climatológica do 8º Distrito de Meteorologia, localizada na Universidade Federal de Santa Maria (29º 43' 23" de latitude Sul e 53º 43' 15" de longitude Oeste, altitude 95 m). Analisaram-se as seguintes funções de distribuição de probabilidade: gama, Weibull, normal, log-normal e exponencial. As funções que melhor descreveram a distribuição das probabilidades foram gama e Weibull. O maior número de dias com chuva ocorreu durante os meses de inverno porém o volume de precipitação é menor nesses dias, resultando em total mensal semelhante para todos os meses do ano.

Validação do modelo ClimaBR em relação ao número de dias chuvosos e à precipitação total diária

Este trabalho foi realizado com o objetivo de validar o modelo ClimaBR no que se refere à geração de séries sintéticas de precipitação total diária em diferentes localidades brasileiras. Para tanto, foram geradas séries sintéticas de precipitação para 12 localidades, escolhidas de forma distribuída, para que todas as diferentes regiões de precipitação homogênea do País fossem contempladas. A partir das séries pluviométricas, disponíveis nas estações meteorológicas das localidades selecionadas, o ClimaBR foi utilizado para gerar as séries sintéticas de precipitação, sendo gerada uma série de 100 anos para cada localidade. A qualidade dos resultados foi analisada comparando-se o ajuste entre os valores observados e os gerados pelo ClimaBR, por meio de regressão linear simples e de outros indicadores estatísticos. Os resultados obtidos permitem afirmar que, de acordo com as condições consideradas no presente estudo, o modelo ClimaBR apresentou bom desempenho na geração de séries sintéticas de precipitação (número de dias chuvosos e precipitação total diária) para todas as localidades testadas.

Scaling from process timescales to daily time steps: A distribution function approach

A new temporal scaling method applicable to many rainfall‐runoff‐erosion models is presented. The method is based on the probability distribution approach used in a number of spatial hydrological models, and it uses statistical distributions of rainfall intensity to represent subdaily intensity variations in a daily time step model. This allows the effect of short timescale nonlinear processes to be captured while modeling at a daily time step, which is often attractive due to the wide availability of total daily rainfall data. The approach relies on characterizing the rainfall intensity variation within a day using a probability distribution function (pdf). This pdf is then modified by various linear and nonlinear processes typically represented in hydrological and erosion models. The statistical description of subdaily variability is thus propagated through the model, allowing the effects of variability to be captured in the simulations. This results in pdfs of various fluxes, the integration of which over a day gives respective daily totals. The method is tested using 42 plot years of daily runoff and erosion plot data from field studies in different environments from Australia and Nepal. Significant improvements in the simulation of surface runoff and erosion are achieved, compared with a similar model using average daily rainfall intensities. The probability‐based model compares well with a subhourly (2 and 6 min) model using similar process descriptions. This suggests that the probability‐based approach captures the important effects of sub–time step variability while utilizing commonly available information. It is also found that the model parameters are more robustly defined using the probability‐based approach compared with the daily effective parameter model. This suggests that the probability‐based approach may offer improved model transferability spatially (to other areas) and temporally (to other periods).

The coincidence of daily rainfall events in Liberia, Costa Rica and tropical cyclones in the Caribbean basin

The occurrence of tropical cyclones in the Caribbean and North Atlantic basins has been previously noted to have a significant effect both upon individual hydro-climatological events as well as on the quantity of annual precipitation experienced along the Pacific flank of Central America. A methodology for examining the so-called ‘indirect effects’ of tropical cyclones (i.e. those effects resulting from a tropical cyclone at a considerable distance from the area of interest) on a daily rainfall record is established, which uses a variant of contingency table analysis. The method is tested using a single station on the Pacific slope of Costa Rica. Employing daily precipitation records from Liberia, north-western Costa Rica (1964–1995), and historic storm tracks of tropical cyclones in the North Atlantic, it is determined that precipitation falling in coincidence with the passage of tropical depressions, tropical storms, and hurricanes accounts for approximately 15% of average annual precipitation. The greatest effects are associated with storms passing within 1300 km of the precipitation station, and are most apparent in the increased frequency of daily rainfall totals in the range of 40–60 mm, rather than in the largest daily totals. The complexity and nonstationarity of factors affecting precipitation in this region are reflected in the decline in the number of tropical cyclones and their significance to annual precipitation totals after 1980, simultaneous to an increase in annual precipitation totals. The methodology employed in this study is shown to be a useful tool in illuminating the indirect effects of tropical cyclones in the region, with the potential for application in other areas. Copyright © 2005 Royal Meteorological Society.

Stochastic disaggregation of daily rainfall into one-hour time scale

The Australian SILO Data Drill facility generates continuous daily rainfall data from 1889 to current date for any set of coordinates on the Australian continent. For the daily rainfall data to have any appeal to users, such as farmers and environmental modellers, a robust disaggregation model that generates sub-daily time series fully consistent with the daily totals while preserving multiple sub-daily time scale stochastic structure is required. A model, which incorporates repetition techniques and a proportional adjusting procedure [Koutsoyiannis, D., Onof, C., 2001. Rainfall disaggregation using adjusting procedures on a Poisson cluster model. J. Hydrol. 246, 109–122] into a regionalised hybrid model [Gyasi-Agyei, Y., 1999. Identification of regional parameters of a stochastic model for rainfall disaggregation. J. Hydrol. 223(3–4), 148–163], has been demonstrated to have such capability. The model is structured such that clusters of consecutive wet days can be disaggregated together during the generation of the binary wet and dry sequence and/ or intensity phases. Two ad hoc remedies to prevent overestimation of the variance and the extreme values, and underestimation of the autocorrelation that could be potentially caused by daily rainfall totals in excess of the hourly maximum have been proposed. The model was evaluated with a 5-year time series of hourly rainfall observed at an erosion control experimental site. All modes of operation of the model reproduced the dry probability very well. Clustering does not seem to affect the dry probability, variance and the intensity-duration–frequency (IFD) curves. The reproduction of the autocorrelations certainly improved with clustering. Capping the hourly rainfall depths to the observed maximum values reproduced near perfect dry probability, variance, autocorrelation and the IFD curves for all months. With this confidence, the 114-year synthetic daily rainfall data set for Rockhampton generated by SILO Data Drill facility was disaggregated to one-hour time scale. The pattern of the results from this data set was identical to that of the observed 5-year data set.

The predictability of deep convection in cloud‐resolving simulations over land

AbstractCloud‐resolving models (CRMs) can be used to provide subgrid information for use in improving the representation of convection in large‐scale models. However, it is shown here that, for a 24‐hour simulation of convection over land, the total daily rainfall and instant rain rates can often be hard to predict. An ensemble of 2D CRM runs, which differ only in the initial white‐noise temperature perturbations added to the lowest 200 m, show a large spread of results. The size of the spread is shown to be dependent on the nature and strength of the forcing with the most significant differences between ensemble members when only a small number of convective cells exist in the domain. Further sensitivity experiments show that stronger forcing or increased domain size can reduce the spread of results due to an increased number of clouds. However, in all the simulations described in this paper, convection tended to organize into fewer but larger clouds during the day and, as this occurs, the ensemble members began to diverge even with a domain size of 1000 km. © Crown copyright, 2004.

Land use change and hydrological response in the Camel catchment, Cornwall

The paper attempts to determine the extent to which rainfall trends and land use changes influence the river flow regime and flood response of a predominantly agricultural catchment (210 km 2 ) in southwest England. Temporal changes in daily rainfall totals were analysed over annual, seasonal and monthly timescales but although annual average October rainfalls exhibited a weak rising trend ( r =0.3, p >0.05), no long-term patterns were observed. Analysis of daily mean discharge data for the River Camel over the period 1965–2000, using the Gumbel distribution, revealed an increase in the magnitude and frequency of peak flows. Land use changes were examined using Agricultural Census Data for 1969, 1979, 1988, 1997 and 2000. Both the number of stock and the area under cereals increased from 1969 to 1997, but cereal production declined substantially between 1997 and 2000. Spatial response patterns were also examined through a comparison of the flow response of the entire Camel catchment with its more complex land use, with the predominantly pastoral De Lank headwater sub-catchment (22 km 2 ), to ascertain the amount of change due to increased livestock numbers alone. No single factor was found to be responsible for the increases in flood frequency and magnitude in the River Camel. Rather, long-term changes in the response of the Camel system appear to emanate from the cumulative impact of subtle changes in climate, combined with increased farming activity plus urban expansion. The paper highlights the inherent difficulties of attempting to disentangle the precise effects of individual land uses on flood responses at the catchment scale and underlines the need for a holistic approach to the management of floods. By the same token, sustainable catchment management can only be achieved through greater awareness of the potential for complex, small-scale land use decisions to result in large-scale hydrological changes.

Land use change and hydrological response in the Camel catchment, Cornwall

The paper attempts to determine the extent to which rainfall trends and land use changes influence the river flow regime and flood response of a predominantly agricultural catchment (210 km 2) in southwest England. Temporal changes in daily rainfall totals were analysed over annual, seasonal and monthly timescales but although annual average October rainfalls exhibited a weak rising trend ( r=0.3, p>0.05), no long-term patterns were observed. Analysis of daily mean discharge data for the River Camel over the period 1965–2000, using the Gumbel distribution, revealed an increase in the magnitude and frequency of peak flows. Land use changes were examined using Agricultural Census Data for 1969, 1979, 1988, 1997 and 2000. Both the number of stock and the area under cereals increased from 1969 to 1997, but cereal production declined substantially between 1997 and 2000. Spatial response patterns were also examined through a comparison of the flow response of the entire Camel catchment with its more complex land use, with the predominantly pastoral De Lank headwater sub-catchment (22 km 2), to ascertain the amount of change due to increased livestock numbers alone. No single factor was found to be responsible for the increases in flood frequency and magnitude in the River Camel. Rather, long-term changes in the response of the Camel system appear to emanate from the cumulative impact of subtle changes in climate, combined with increased farming activity plus urban expansion. The paper highlights the inherent difficulties of attempting to disentangle the precise effects of individual land uses on flood responses at the catchment scale and underlines the need for a holistic approach to the management of floods. By the same token, sustainable catchment management can only be achieved through greater awareness of the potential for complex, small-scale land use decisions to result in large-scale hydrological changes.

The influence of temperature, relative humidity and rainfall on the occurrence of pollen allergens (Betula, Poaceae, Ambrosia artemisiifolia) in the atmosphere of Bratislava (Slovakia).

The occurrence of pollen grains in the atmosphere markedly relates to meteorological factors. In the study we have evaluated a correlation between the concentration of pollen grains in the atmosphere of Bratislava and temperature, relative humidity and rainfall during the vegetation period of 1995 and 1997. For our analysis we have selected one representative of each phytoallergen group (trees, grasses, weeds). We have chosen the Betula genus of trees, the whole Poaceae family of grasses and ragweed Ambrosia artemisiifolia L. to represent weeds. The taxons mentioned represent the most significant allergens in Slovakia. The concentration of pollen grains has been monitored by a Lanzoni volumetric pollen trap. The data obtained, the average daily concentration in 1 m(3), have been included in the statistical analysis together with values for the average daily temperature, relative humidity and total rainfall in 24 h. The correlation between the concentration of pollen grains in the atmosphere and selected meteorological variables from daily monitoring has been studied with the help of linear regression and correlation coefficients. We have found the average daily temperature and relative humidity (less than temperature) to be significant factors influencing the occurrence of pollen grains in the atmosphere of Bratislava. The total daily rainfall does not seem to be significant from the statistical point of view.

A parsimonious approach to stochastic multisite modelling and disaggregation of daily rainfall

Daily rainfalls are simulated through a two station model at a key station and satellite stations whilst maintaining the first three moments and relevant correlations. Wet and dry runs of the occurrence process of daily rainfall are assumed to have a geometric distribution. Disaggegration of daily rainfalls into hourly values is made through dimensionless accumulated hourly amounts generated by a beta distribution. It is postulated that the occurrence process of hourly rainfall has also a geometric distribution but it is conditioned on the total daily rainfall. Application is made to the Tevere (Tiber) basin in central Italy. The simple reduced parameter approach is seen to reproduce satisfactorily extremes and other statistical properties of daily and hourly rainfalls.

The relationship between synoptic scale airflow direction and daily rainfall: a methodology applied to Devon and Cornwall, South West England

Trans-scale relationships are established between fluctuations in the direction of the geostrophic flow over the British Isles and spatial variations in rainfall over Devon and Cornwall, South West England. The rationale for using such an approach is to provide the basis for assessing changes to the region’s rainfall climatology that may result from possible future enhanced greenhouse effect forced alterations to large-scale wind flow patterns. A new method, the concentration factor (CF), that relates rainfall totals to the frequency of the flow, is applied to investigate spatial variations in rainfall totals at twelve stations in the two counties under eight wind direction groups (N, NE, E, SE, S, SW, W, NW). S and SW flow types are found to produce the highest daily rainfall totals at all locations, with the three easterly groups (NE, E, SE) yielding higher daily precipitation intensities than the maritime NW group. Inter-annual and seasonal variations in daily wind direction – rainfall (WD/R) relationships are then assessed at two contrasting sites in Cornwall (St. Mawgan, Culdrose) using 40 years of data (1957–96). In general, there is a trend over this period toward maritime airflows (S, SW, W, NW) producing higher daily rainfall totals, with the continental groups (N, NE, E, SE) yielding lower totals relative to their frequency of occurrence. The trend toward maritime airflows producing higher rainfall totals is in line with recent trends in the North Atlantic Oscillation (NAO). Notable seasonal variations in WD/R relationships over Cornwall are interpreted in terms of the location’s exposure to the prevailing wind, sea temperature variations and the orography of the South West Peninsula.

Improving Tropical Precipitation Forecasts from a Multianalysis Superensemble

Abstract This paper utilizes forecasts from a multianalysis system to construct a superensemble of precipitation forecasts. This method partitions the computations into two time lines. The first of those is a control (or a training) period and the second is a forecast period. The multianalysis is derived from a physical initialization–based data assimilation of “observed rainfall rates.” The different members of the reanalysis are produced by using different rain-rate algorithms for physical initialization. The basic rain-rate datasets are derived from satellites’ microwave radiometers, including those from the Tropical Rainfall Measuring Mission (TRMM) satellites and the Special Sensor Microwave Imager (SSM/I) data from three current U.S. Air Force Defense Meteorological Satellite Program (DMSP) satellites. During the training period, 155 experiments were conducted to find the relationship between forecasts from the multianalysis dataset and the best “observed” estimates of daily rainfall totals. This re...

Outdoor airborne fungal spores in Singapore

A continuous sampling of airspora in Singapore was carried out over a period of 5 years at 3 different sites. Fungal spores were found to be numerically dominant, comprising between 86.0–89.4% of the total airspora which also consisted of spores of fern and pollen grains. Conidia of Cladosporium were the most abundant fungal spore type, followed by the ascospores of Didymosphaeria and the conidia of Curvularia, Drechslera and Pithomyces. Variations in fungal spore counts were discernible. Two periods of high spore densities were observed annually; in the months of February‐March, and October‐November. Minor peak periods were observed occasionally in April and July‐August. The seasonal trends of the 5 most common fungi generally coincided with these same peak periods for spore counts. Correlation analysis showed that fungal spore counts were influenced by meteorological factors, especially temperature and relative humidity. In particular, Didymosphaeria ascospore counts were positively correlated with relative humidity and total daily rainfall, and inversely correlated with temperature and wind speed. Conversely, Curvularia, Drechslera and Pithomyces spore counts decreased with increases in relative humidity and precipitation. The spore counts of Curvularia and Cladosporium were also positively correlated with temperature, while those of Drechslera were positively correlated with wind speed. This study revealed the existence of a rich fungal airspora in Singapore.

Climatic Aspects of the 1993 Upper Mississippi River Basin Flood

Abstract The 1993 record-breaking summer flood in the Upper Mississippi River Basin resulted from an unprecedentedly persistent heavy rain pattern. Rainfall totals for the Upper Mississippi River Basin were, by a large margin, the largest of this century for the 2-, 3-, 4-, and 12- month periods encompassing the 1993 summer. The totals for these periods are estimated to have a probability of occurrence of less than 0.005 yr−1. In addition, the number of reporting stations receiving weekly totals in excess of 100 mm (events identified in a previous study as being closely correlated with floods) was the largest in at least the last 45yr. Other conditions contributing to the flood include above-normal soil moisture levels at the beginning of June 1993; large-sized areas of moderate to heavy rains; occurrence of rain areas oriented along the main stems of major rivers; a large number of localized extreme daily rainfall totals (greater than 150 mm); and below-normal evaporation. The large-scale atmospheric cir...

Effective fractal dimension and corrections to the mean of annual maxima

Given a time series of daily rainfall totals, it is recognized that the maximum daily value is, in general, lower than the true 24 h maximum. Thus, annual maximum series under-represent the extreme events, and correction factors are therefore required to convert them to their 24 h counterparts. The phenomenon is generalized and examined by reference to UK time series for rainfall, wind speed and air temperature, resulting in mean correction factors of 1.167, 1.099 and 1.036, respectively. For air temperature, the result is influenced by the choice of datum. In general, such correction factors are unavailable, and so the effective fractal dimension, d, of the data is investigated as a means through which to predict them; the correlation found is promising.

East Australian Rainfall Events: Interannual Variations, Trends, and Relationships with the Southern Oscillation

Abstract The number, average length, and average intensity of rain events at five stations located in eastern Australia have been calculated for each year from 1910 to 1988, using daily rainfall totals. A rain event has been defined as a period of consecutive days on which rainfall has been recorded on each day. Inter-relationships between the rain-event variables (at each station and between stations), along with their relationships with annual rainfall and the El Nino-Southern Oscillation, have been investigated. Trends in the time series of the rain-event variables have also been examined. Annual rainfall variations are found to be primarily caused by variations in intensity. Fluctuations in the three rain-event variables are essentially independent of each other. This is due, in some cases, to inter-relationships at interdecadal time scales offsetting relationships of the opposite sense at shorter time scales. The large-scale geographical nature of east Australian rainfall fluctuations mainly reflects...