Heavy Rain Days Research Articles

Variability and trends of extreme precipitation events over Bulgaria (1961–2005)

Heavy precipitation events often lead to river floods and flash floods causing significant loss of life and property damage, landslide activation, and other social and economic problems. The upward tendency of damages, caused by natural disasters, supports the idea that extreme events, associated with the effects of climate change, have recently occurred with greater frequency. The series of hazardous precipitation events which affected the Balkans and in particular Bulgaria in 2005 show that further study of such type of phenomena is necessary in order to improve their predictability. The subject of the present study is the variability and the trends associated with extreme precipitation events in Bulgaria during the period 1961–2005. Total precipitation amounts exceeding 30 mm/day which occur in 4 or more provinces of the country are considered to be risky for floods. We call them here heavy-rain days or events. The regime of such potentially dangerous heavy-rain/snow events is compared to those of total precipitation amounts for two periods: 1961–1990 and 1991–2005. Significant increase (more than 32%) of the days with heavy 24-hour precipitation is revealed during the second period, while the total annual rainfall is almost without changes or shows a slightly decreasing trend in many regions of the country. Besides, the contribution of heavy and torrential rain/snow to the observed annual precipitation totals increases. It is in contrast with the observed trend of decrease for the weak and moderate precipitation amounts. Two typical synoptic situations, leading to such type of extreme events in the extreme year 2005 are presented. The first is a “winter” one in February and the second – a “summer” one in July.

Effect of the Zagros Mountains on the spatial distribution of precipitation

In order to examine the effect of the Zagros Mountains on precipitation, first, the annual and seasonal rainfall indices (rain days frequency, rain amount, daily rainfall intensity, and heavy rains) from 43 stations in 1995 - 2004 between the 30 degrees N to 35 degrees N parallels over the mountain range were analyzed. Second, the effect of the Zagros Mountains was studied through the computation of the spatial correlations between the precipitation parameters and the topographic indices (station site elevation, station mean elevation within a radius of 2.5 km, mean elevation of 9 blocks along each of the eight Cartesian directions, and the elevation differences of these 9 blocks from the station mean elevation). The results showed that in the cold season the maximal rainfall occurs on the upper range of west slope, while in warm season it spreads over the study area. The correlations between precipitation and elevation indices were positive on the north of the stations and negative on the south of the stations, that is, the higher elevations of the stations to the north force the uplifting of the moist air masses and increase rainfall at the stations, while the lower elevations to their south lead the movement of the moist air masses to the stations. This is due to the fact that these stations or slopes are exposed to the moist air masses coming from the Mediterranean Sea and the Persian Gulf. The heavy rain days and the summer sporadic rain events do not show significant correlations with the topographic indices. The findings indicate that the Zagros Mountains intensify the cold period frontal rains especially over the west slope and block the moist air masses from entering the interior parts of the country. Moreover, these mountains play a secondary role in creating rain days. But they are very important in the production of precipitation in the area. Therefore, their absence will decrease the amount of rainfall to their west and, in return, expand the dry climates of their west and east.

Frequency of precipitation and temperature extremes over France in an anthropogenic scenario: Model results and statistical correction according to observed values

Météo-France atmospheric model ARPEGE/Climate has been used to simulate present climate (1961–1990) and a possible future climate (2071–2100) through two ensembles of three 30-year numerical experiments. In the scenario experiment, the greenhouse gas and aerosol concentrations are prescribed by the so-called SRES-A2 hypotheses, whereas the sea surface temperature and sea ice extent come from an earlier ocean–atmosphere coupled simulation. The model covers the whole globe, with a variable resolution reaching 50 to 60 km over France. Model responses on daily minimum and maximum temperature and precipitation are analyzed over France. The distribution of daily values is compared with observed data from the French climatological network. The extreme cold temperatures and summer heavy precipitations are underestimated by the model. A correction technique is proposed in order to adjust the simulated values according to the observed ones. This process is applied to both reference and scenario simulation. Synthetic indices of extreme events are calculated with corrected simulations. The number of heavy rain (> 10 mm) days increases by one quarter in winter. The maximum length of summer dry episodes increases by one half in summer. The number of heat wave days is multiplied by 10. The response in precipitation is less when only the change in the mean is considered. Such a corrected simulation is useful to feed impact models which are sensitive to threshold values, but the correction does not reduce, and may enhance in some cases, the uncertainty about the climate projections. Using several models and scenarios is the appropriate technique to deal with uncertainty.

Meteorological monitoring of an active volcano: Implications for eruption prediction

Rainfall data collected on and around the Soufriere Hills Volcano, Montserrat between 1998 and 2003 were analysed to assess the impact on primary volcanic activity, defined here as pyroclastic flows, dome collapses, and explosions. Fifteen such rainfall-triggered events were identified. If greater than 20 mm of rain fell on a particular day, the probability of a dome collapse occurring on that day increased by a factor of 6.3% to 9.2%, compared to a randomly chosen day. Similarly, the probability of observing pyroclastic flows and explosions on a day with > 20 mm of rainfall increased by factors of 2.6 and 5.4, respectively. These statistically significant links increased as the rainfall threshold was increased. Seventy percent of these rainfall-induced dome collapse episodes occurred on the same calendar day (most within a few hours) as the onset of intense rainfall, but an extra 3 occurred one or two calendar days later. The state of the volcano was important, with the rainfall–volcanic activity link being strongest during periods of unstable dome growth and weakest during periods of no dome growth or after a recent major collapse. Over 50% of the heavy rain days were associated with large-scale weather systems that can potentially be forecast up to a few days ahead. However, the remaining heavy rain days were associated with small-scale, essentially unpredictable weather systems. There was significant variability in the amount of rainfall recorded by different rain gauges, reflecting topographic variations around the volcano but also the inherent small-scale variability within an individual weather system. Hence, any monitoring/warning program is recommended to use a network, rather than just a single gauge. The seasonal cycle in rainfall was pronounced, with nearly all the heavy rain days occurring in the May–December wet season. Hence, the dome was at its most vulnerable at the beginning of the wet season after a period of uninterrupted growth. Interannual variability in rainfall was related to tropical Pacific and Atlantic sea surface temperature anomalies, and holds out the prospect of some limited skill in volcanic hazard forecasts at even longer lead times.

Water balance and water movement in unsaturated zones of Sphagnum hummocks in Fuhrengawa Mire, Hokkaido, Japan

This study examined the hydrological conditions and water balance of a tall hummock in Fuhrengawa mire for 2 years. We clarified the hydrological processes by which Sphagnum can survive on hummocks of a mixed mire. Surface-layer water content was almost constant irrespective of continuous sunny days and heavy-rain days. Water content of deeper layers and the overall water level fluctuated more widely. Estimates of water balance showed that an almost identical amount of water that was lost to evapotranspiration was re-supplied from deeper layers to the surface on sunny days. Conversely, during rainy periods, rainwater rapidly infiltrated through unsaturated layers to deeper layers. Thereby, some fraction of the rainwater was stored in deeper layers or as groundwater. These water movements are attributable to the physical properties of Sphagnum peat, which forms hummocks. During our 2-year observation, precipitation was 1.1–1.5 times higher than the evapotranspiration. The longest period without rainfall was 11 days. Such a frequent and abundant rainwater supply, which exceeds evapotranspiration loss, maintains wet conditions and quantitative predominance of rainwater in hummocks. Accordingly, Sphagnum hummocks in the Fuhrengawa mire maintain their wet and ombrotrophic conditions because of the physical properties of peat and humid climate. Sphagnum survives because of these suitable conditions for growth.

Diurnal Variation of Precipitable Water over a Mountainous Area of Sumatra Island

Diurnal variations in atmospheric water vapor at Koto Tabang, a mountainous area of Sumatra Island, Indonesia, are studied by analyzing the GPS-derived precipitable water, radiosonde data, and surface meteorological observation data. A permanent GPS receiving station was established at Koto Tabang in March of 2001. Radiosonde soundings were carried out at 3-h intervals to study the atmospheric water and energy cycles in the Maritime Continent of Indonesia. A distinct diurnal variation in water vapor is observed. The precipitable water increases during daytime, reaching its maximum in the late afternoon. The results of the radiosonde observations indicate that the increase in water vapor occurs up to an altitude of approximately 3 km. Water vapor is transported by turbulent mixing with the development of the boundary layer in the afternoon. The diurnal cycle of water vapor is affected by the intensity of incident solar radiation. It is suggested that the diurnal variation in water vapor is caused by the horizontal transport of water vapor by local circulation. The diurnal range of the precipitable water on days with heavy rain was larger than that on days without rain. Rainfall often occurs as intensive showers during a short period in the late afternoon and early evening in the Koto Tabang area; daily shortwave radiation is still sufficiently strong to generate the local circulations and to induce large diurnal variation in precipitable water, even on the heavy-rain days.

Integrating complexity of social systems in natural hazards planning: An example from Caracas, Venezuela

In December 1999, days of heavy rain on steep slopes north of Caracas, Venezuela triggered massive mud and debris flows, killing tens of thousands. Partly in response to this disaster, a multidisciplinary team of urban planners and Earth scientists from Columbia University recently developed a framework plan for building disaster resilience into the Venezuelan capital region. After assessing the complex intersection of urban geography with severe seismic and hydrologic hazards, substantial recommendations were made to local and regional authorities on future hazards mitigation.Areas found most at risk in the Caracas region include the transportation and utility infrastructure and the friable building stock of squatter settlements. Recognizing realistic economic and socio‐political constraints on implementing change, a prioritized list of goals and activities was constructed, and recommendations made along various time scales. Immediate disaster‐avoidance goals (to be completed within 1 to 5 years) include strengthening critical infrastructure nodes, housing stock, and emergency services. More intermediate goals (5 to 10 years) focus on upgrading fragile housing units, creating detailed hazard maps across the city, and incorporating disaster education into cultural activities. Recommended activities for the long term (beyond 10 years) include creating a fully redundant transportation and water delivery network, establishing legitimate land title for squatters, and re‐locating critical facilities currently in high‐risk areas.

Photosynthetic productivity of the epilithic lichen Lecanora muralis: long-term field monitoring of CO2 exchange and its physiological interpretationIII. Diel, seasonal, and annual carbon budgets

Summary Carbon dioxide exchange of the epilithic, green algal lichen Lecanora muralis and the weather conditions in its natural habitat in the Botanical Garden, Wurzburg (Bavaria, Germany), were monitored by means of an automatic cuvette. The continuity of the data over a total of 15 months of measurements enabled integrals to be calculated of diel, monthly, seasonal, and annual sums of photosynthetic carbon income (σNP), respiratory carbon loss (σDR) and carbon budget (net primary production, σC = σNP – σDR). Annual σNP for the period July 1995 through June 1996 was 50021 mg m −2 year −1 but respiratory processes lost 57% of this so that σC amounted to 21494 mg m −2 year −1 (20.7% of thallus carbon content). If summer 1996, which had a much smaller productivity than summer 1995, is included, annual σC was only 15.8% of carbon content for the period October 1995 through September 1996. The lichen showed extremely high variability in its daily CO 2 exchange, and performance depended almost completely on the momentary hydration conditions. Diel σNP and σC were not greatly influenced by thallus temperature, and manner of moistening was more important than high PPFD. Days with favourable primary production occurred in all seasons. Negative diel σC was frequent through the year and carbon loss occurred on 25%; of the 274 days of the year on which the lichen was metabolically active. The various weather response types, because of their characteristic influence on the mode and extend of thallus hydration, differed considerably in their contribution to the annual carbon balance of the lichen. 74 days of heavy rain during the year produced only 4.2%; of the annual σC, because, under such conditions, σDR was high and σNP was limited by depression of thallus gas exchange due to suprasaturation. In contrast, days with dew (40.0% of annual σC in 105 days) or those with nocturnal rain and subsequent drying (28.5% in 57 days) were the best contributors to annual σC. Differences in the frequency of occurrence of the different weather condition types through the year meant that lichen productivity apparently followed a seasonal pattern, each season resulting in a positive carbon balance. Autumn and summer 1995 were the most productive seasons, and the lowest was spring with no more than 18% of the autumn production. In summer, the season which was covered twice during the measurements, σC was less than one fourth in 1996 of that in 1995, underlining the high variability in the photosynthetic production of the lichen. Thus, firm generalisations are still not possible about seasonality of production for this species. There was no correlation between monthly σC and monthly rainfall. Due to the complex interdependencies of CO 2 exchange of L. muralis simple predictions of its carbon budget from meteorological standard data are likely to be very difficult or even impossible.

Photosynthetic productivity of the epilithic lichen Lecanora muralis: long-term field monitoring of CO 2 exchange and its physiological interpretation : III. Diel, seasonal, and annual carbon budgets

Carbon dioxide exchange of the epilithic, green algal lichen Lecanora muralis and the weather conditions in its natural habitat in the Botanical Garden, Würzburg (Bavaria, Germany), were monitored by means of an automatic cuvette. The continuity of the data over a total of 15 months of measurements enabled integrals to be calculated of diel, monthly, seasonal, and annual sums of photosynthetic carbon income (σNP), respiratory carbon loss (σDR) and carbon budget (net primary production, σC = σNP – σDR). Annual σNP for the period July 1995 through June 1996 was 50021 mg m−2 year−1 but respiratory processes lost 57% of this so that σC amounted to 21494 mg m−2 year−1 (20.7% of thallus carbon content). If summer 1996, which had a much smaller productivity than summer 1995, is included, annual σC was only 15.8% of carbon content for the period October 1995 through September 1996. The lichen showed extremely high variability in its daily CO2 exchange, and performance depended almost completely on the momentary hydration conditions. Diel σNP and σC were not greatly influenced by thallus temperature, and manner of moistening was more important than high PPFD. Days with favourable primary production occurred in all seasons. Negative diel σC was frequent through the year and carbon loss occurred on 25%; of the 274 days of the year on which the lichen was metabolically active. The various weather response types, because of their characteristic influence on the mode and extend of thallus hydration, differed considerably in their contribution to the annual carbon balance of the lichen. 74 days of heavy rain during the year produced only 4.2%; of the annual σC, because, under such conditions, σDR was high and σNP was limited by depression of thallus gas exchange due to suprasaturation. In contrast, days with dew (40.0% of annual σC in 105 days) or those with nocturnal rain and subsequent drying (28.5% in 57 days) were the best contributors to annual σC. Differences in the frequency of occurrence of the different weather condition types through the year meant that lichen productivity apparently followed a seasonal pattern, each season resulting in a positive carbon balance. Autumn and summer 1995 were the most productive seasons, and the lowest was spring with no more than 18% of the autumn production. In summer, the season which was covered twice during the measurements, σC was less than one fourth in 1996 of that in 1995, underlining the high variability in the photosynthetic production of the lichen. Thus, firm generalisations are still not possible about seasonality of production for this species. There was no correlation between monthly σC and monthly rainfall. Due to the complex interdependencies of CO2 exchange of L. muralis simple predictions of its carbon budget from meteorological standard data are likely to be very difficult or even impossible.

Changes of extreme events in regional climate simulations over East Asia

Changes of extreme events due to greenhouse effects (2 × CO2) over East Asia, with a focus on the China region as simulated by a regional climate model (RegCM2), are investigated. The model is nested to a global coupled ocean-atmosphere model (CSIRO R21L9 AOGCM). Analysis of the control run of the regional model indicates that it can reproduce well the extreme events in China. Statistically significant changes of the events are analyzed. Results show that both daily maximum and daily minimum temperature increase in 2 × CO2 conditions, while the diurnal temperature range decreases. The number of hot spell days increases while the number of cold spell days decreases. The number of rainy days and heavy rain days increases over some sub-regions of China. The 2 × CO2 conditions also cause some changes in the tropical storms affecting China.

Intra‐seasonal rainfall characteristics and their importance to the seasonal prediction problem

AbstractDaily station rainfall data in South Africa from 1936 to 1999 are combined into homogeneous rainfall regions using Ward's clustering method. Various rainfall characteristics are calculated for the summer season, defined as December to February. These include seasonal rainfall total, region‐average number of station rain days exceeding 1 and 20 mm, region‐average of periods between rain days at stations >1 and >20 mm, region‐average of wet spell length (sequential days of station rainfall >1 and >20 mm), correlation of daily station rainfall within a region and correlation of seasonal station rainfall anomalies within a region.Rank‐ordered rainfall characteristic data generally form an s‐shaped curve, and significance testing of discontinuities in these curves suggests that normal rainfall conditions in South Africa consist of a combined middle three quintiles separated from the outer quintiles, rather than the traditional middle tercile.The relationships between the various rainfall characteristics show that seasons with a high total rainfall generally have a higher number of heavy rain days (>20 mm) and not necessarily an increase in light rain days. The length of the period between rain days has a low correlation to season totals, demonstrating that seasons with a high total rainfall may still contain prolonged dry periods. These additional rainfall characteristics are important to end‐users, and the analysis undertaken here offers a valuable starting point for seeking physical relationships between rainfall characteristics and the general circulation. Preliminary studies show that the vertical mean wind is related to rainfall characteristics in South Africa. Given that general circulation models capture this part of the circulation adequately, seasonal forecasts of rainfall characteristics become plausible. Copyright © 2002 Royal Meteorological Society.

Impact of climate on thermal rhythm in pastoral sheep

The effects of environmental conditions on temperature rhythms were investigated in ewe lambs at pasture. Two groups of 20 lambs had heart rate (HR), vaginal temperature ( T v), ear-canal temperature ( T c) and ear-pinna temperature ( T p) monitored continuously for 3 days. Climatic conditions were recorded at the same time and Temperature Humidity Index (THI) calculated. One group experienced fine clear weather for the 3 days, the other group experienced 2 days of heavy rain. During periods of fine weather, the daily rhythm for T v and T c was monophasic. However, heavy rain and a constant THI reduced the amplitude of the recorded temperature rhythms. Daily T v and T c patterns correlated strongly with THI, with a phase lag of 2 h. Peak T v and T c were at approximately 17:00 h each day. Mean maximum daily amplitudes were approximately 1.3 °C for T v and T c. Mean T v was 39.3±0.1 and 39.6±0.1 for weeks 1 and 2, respectively, while mean T c was 38.9±0.1 and 39.2±0.1. Changes in T v and T c were closely correlated. We conclude that climate has a major effect on body temperature rhythms.

Australian Heavy-Rain Days and Associated East Coast Cyclones: 1958–92

Abstract The authors present a comprehensive climatology of heavy rain and east coast cyclones from January 1958 to September 1992. A total of 80 cyclones, including nondeveloping systems, were objectively identified from daily rainfall and surface wind observations at 28 stations along the east coast of Australia. The method used first identifies heavy-rain days, then uses the wind observations to differentiate east coast cyclones from other rain-producing systems. This method is found to be reliable and with modifications may be used to identify other mesoscale systems. In general, onshore southeasterly to southerly flow is most commonly associated with heavy rain along the east coast of Australia. Local convective heavy-rain events are most common in the Tropics, and the maximum occurrence of heavy-rain days propagates poleward from summer to winter. The latitudinal position and movement of the subtropical anticyclone, and variations in the Southern Oscillation index, have been found to be major factor...

The Potential Use of Summer Rainfall Enhancement in Illinois. Part I: A Field Experiment to Define Responses of Crop Yields to Increased Rainfall

An assessment was made of factors affecting the use of cloud seeding to increase summer (June-August) rainfall for improved corn and soybean yields in Illinois. Crop yields from a five-year agricultural field experiment involving nine levels of rain increases were compared with yields produced under natural rainfall. The sampled years (1987-91) included a wide range of summer weather conditions, including extremely hot and dry (1988) and very wet and cool (1990). Since the types of growing seasons sampled represented only 30% of all types, caution must be used in interpreting the results and applying them to other years. Additional water of 10%, 25%, or 40% of each days actual rainfall was applied after each rain. Additional water was also applied only to certain rains, depending on whether they were light, moderate, or heavy. The best treatment, based on performance in all years and considering both treated and untreated crops, was a 25% rain increase applied on days with moderate rain (2.5 mm-2.53 cm). However, it was only marginally better than the natural rainfall. The best treatment for soybeans alone, based on the average yields for 1987-90, was the natural, unmodified rainfall, whereas that for corn was 10%-40% increases only onmore » heavy-rain days. In general, rain increases of 10% had little yield effect, and 40% increases applied in all years were found damaging in wetter years. However, in extremely dry summers, the 40% rain increases were the best for both crops. The best treatment in any given summer varied by the type and timing of rain conditions and crop. Selection of the best treatment to use in any summer would require the capability to predict the amount and timing of summer rainfall by 1 June. 23 refs., 2 figs., 9 tabs.« less

Evaluation of fungicides for control of South American leaf blight of Hevea brasiliensis

SUMMARYOf 43 fungicides tested in vitro, 19 showed strong, seven moderate and 17 weak inhibition of germination of conidia and ascospores of Microcyclus ulei. The formation of lesions on Hevea brasiliensis leaf discs was also suppressed by the first category of fungicides as well as by the five adjuvants tested. Ascospores were not released when perithecia were treated with urea, thiabendazole or alcoholic mercury chloride at 10.00, 0.10, 1.00 g/1 respectively; other fungicides had no such inhibitory effect.In field trials, thiophanate methyl (0.07% a.i.) and benomyl (0.025% a.i.) were most effective in controlling leaf infection, followed by chlorothalonil (0.15% a.i.) and mancozeb (0.32% a.i.). Benomyl suppressed conidial sporulation, whereas one application of thiophanate methyl (0.14% a.i.) to perithecia inhibited ascospore release; half of this concentration applied to conidial lesions or pycnidia caused the perithecia formed subsequently to abort. Thiophanate methyl thus shows promise for SALB control and elimination and benomyl may be valuable as a supplement in later rounds of spraying to control conidial sporulation.After 6 days of showery rain (2 mm for 17 min per day), water collected from sprayed leaves still gave complete inhibition of spore germination. However, inhibition was markedly reduced after 6 days of heavy rain (over 8 mm for 24 min per day).

Precipitation Modification By Major Urban Areas

Abstract Historical weather records at eight American urban areas of varying size, type, and climate were studied for indications of inadvertent precipitation modification. The six largest cities all had experienced warm seasonal rainfall increases of 9 to 17% during the 1955–70 period. The increases in the Midwest cities occurred largely with cold frontal systems, but in the coastal cities they were largely during air mass (non-frontal) conditions. The Midwest increases also were found to occur as enhancement, not initiation, of moderate to heavy rain days. Significant increases in summer thunder-day frequencies (13 to 41%,) and hail-day frequencies (90 to 450%) were found at the six largest cities, and the increases occurred largely in the morning hours. The typical locations of maxima in the Midwest cities were thunder over and near the city, and rain and hail 25 to 55 km downwind. The maxima of all events in coastal cities were in or near the city. Overall, the results suggest that urban precipitation...

Comments on a Paper by E.G. Bowen Entitled "The Influence of Meteoritic Dust on Rainfall". 2

In this Journal Bowen (1953) has recently put forward evidence purporting to show that " there is a marked tendency for heavy falls of rain to occur on certain days rather than on others, and for this pattern to be repeated year after year". It is claimed that these days of heavy rain coincide (within a margin of variation of �2 days) in many parts of the world, and a theory is put forward explaining the supposed phenomenon in terms of world-wide concentrations of dust produced by the impact of known meteor showers on the atmosphere. He suggests that debris from these meteors, partially disintegrated by atmospheric friction at heights of about 100 km, filters down to the tropopause in about 29 days, where it activates or " seeds" rain clouds, so producing heavy rainfall.

Siticulosa Apulia

‘Parched’ Apulia still describes the dominant characteristic of this region of southern Italy as aptly as when Horace wrote. The climate is one of sharp contrasts, especially apparent on the treeless plain round Foggia (the district known as the Capitanata). There, some midwinter snow and a few intermittent days of heavy rain between January and March are offset by almost continuous, and often pitiless, days of sunshine from April to the end of September, with the thermometer reaching 105° in the shade and scorching winds from the North in late summer absorbing what little moisture remains. The average annual rainfall at Foggia is only 18-19 inches, or no more than in parts of lowland Tunisia; but the fertile soil is today intensively cultivated by dry farming, with immense open arable fields. Harvesting begins at the end of May and, as there is often little depth of cultivated soil above the absorbent subsoils, by early in July the dusty ground is baked as hard as iron.