Annual Maximum Monthly Research Articles

Regional Rainfall Frequency Analysis on Seven Sites of Punjab, Pakistan using L-moments

The hydro-meteorological variables of extreme rainfall are not easy to explain due to unexpected changes in climate and varied usage of water with growing population. Regional rainfall frequency analysis is the one such method that is useful for the requirement of more accurate estimates of rainfall yearly or desineally for the regions having lack of fresh water resources. The series of Annual Maximum Monthly Rainfall Totals (AMMRT) has been used for the seven sites of northern Punjab, Pakistan using L-moments. The results of different test, the run test, lag-1 correlation and Mann-Whitney U test illustrate that the data series of the seven sites of northern Punjab were found random and independently and identically distributed and have no serial correlation. Heterogeneity measure exposed that the region is homogeneous and discordancy measure gives the evidence that no site is discordant among the seven. The result of goodness of fit test including L-moment Ratio diagrams, ZDIST statistic and Mean Absolute Deviation Index exposed the Pearson Type III (PE3), Generalized Normal (GNO) and Generalized Extreme Value(GEV) are best suitable of the regional distribution for the quantiles estimation. The quantiles estimates obtained for different return periods. A linear regression model was developed with good fit between the at site characteristics and the mean of the AMMRT of the sites. The estimates of the study may be used for the estimation of the rainfall quantiles of the seven sites for different return periods. The estimates will be useful to design future preventive measures for the harmful impact of hydro meteorological events at these sites in Punjab Pakistan.

Characteristics of Extreme Value Statistics of Annual Maximum Monthly Precipitation in East Asia Calculated Using an Earth System Model of Intermediate Complexity

Extreme precipitation is no longer stationary under a changing climate due to the increase in greenhouse gas emissions. Nonstationarity must be considered when realistically estimating the amount of extreme precipitation for future prevention and mitigation. Extreme precipitation with a certain return level is usually estimated using extreme value analysis under a stationary climate assumption without evidence. In this study, the characteristics of extreme value statistics of annual maximum monthly precipitation in East Asia were evaluated using a nonstationary historical climate simulation with an Earth system model of intermediate complexity, capable of long-term integration over 12,000 years (i.e., the Holocene). The climatological means of the annual maximum monthly precipitation for each 100-year interval had nonstationary time series, and the ratios of the largest annual maximum monthly precipitation to the climatological mean had nonstationary time series with large spike variations. The extreme value analysis revealed that the annual maximum monthly precipitation with a return level of 100 years estimated for each 100-year interval also presented a nonstationary time series which was normally distributed and not autocorrelated, even with the preceding and following 100-year interval (lag 1). Wavelet analysis of this time series showed that significant periodicity was only detected in confined areas of the time–frequency space.

Vegetation dynamics of ephemeral and perennial streams in mountainous headwater catchments

Ephemeral and perennial streams of mountainous catchments in Sabaragamuwa Province of Sri Lanka and Hong Kong of China were studied for two years on vegetation dynamics. Each year, sampling was conducted during a period when ephemeral streams had low surface flows. Sampling was realized contiguously using belt transects. The standing crop biomass (hereafter biomass) of herbaceous vegetation in ephemeral channels was comparatively lower than perennials and so was the herb diversity. Herb diversity showed a peak from 1.5 to 4.5 m from the centerline/thalweg of ephemeral and perennial streams. Out of 24 herbs, only three were common for both. A peak herb biomass zone was observed in perennials in the same region where diversity peaked. In ephemerals, herb biomass increased laterally up to ∼1.5 m, and was constant thereafter. Seedling experiment results tallied with the field diversity observations of both stream types, and suggested that seed dispersion was the main reason for herb colonization. Furthermore, it showed sapling emergence to be significantly higher in perennials than ephemerals. Return period of annual maximum monthly rainfall was a strong indicator of age of trees in ephemeral streams, and elucidated the possibility of hindcasting past flow episodes. Electrical conductivity was significantly high in ephemeral streams among all the water quality parameters. The contents of the water nutrients were approximately the same in both stream types. While recommending further studies on eco-hydrology of ephemerals, we recognize ephemeral streams to be valuable references in climate change studies due to their responsiveness and representativeness in long term hydrological changes.

Impacts of climate change on TN load and its control in a River Basin with complex pollution sources

It is increasingly recognized that climate change could affect the quality of water through complex natural and anthropogenic mechanisms. Previous studies on climate change and water quality have mostly focused on assessing its impact on pollutant loads from agricultural runoff. A sub-daily SWAT model was developed to simulate the discharge, transport, and transformation of nitrogen from all known anthropogenic sources including industries, municipal sewage treatment plants, concentrated and scattered feedlot operations, rural households, and crop production in the Upper Huai River Basin. This is a highly polluted basin with total nitrogen (TN) concentrations frequently exceeding Class V of the Chinese Surface Water Quality Standard (GB3838-2002). Climate change projections produced by 16 Global Circulation Models (GCMs) under the RCP 4.5 and RCP 8.5 scenarios in the mid (2040–2060) and late (2070–2090) century were used to drive the SWAT model to evaluate the impacts of climate change on both the TN loads and the effectiveness of three water pollution control measures (reducing fertilizer use, constructing vegetative filter strips, and improving septic tank performance) in the basin. SWAT simulation results have indicated that climate change is likely to cause an increase in both monthly average and extreme TN loads in February, May, and November. The projected impact of climate change on TN loads in August is more varied between GCMs. In addition, climate change is projected to have a negative impact on the effectiveness of septic tanks in reducing TN loads, while its impacts on the other two measures are more uncertain. Despite the uncertainty, reducing fertilizer use remains the most effective measure for reducing TN loads under different climate change scenarios. Meanwhile, improving septic tank performance is relatively more effective in reducing annual TN loads, while constructing vegetative filter strips is more effective in reducing annual maximum monthly TN loads.

Application of regional rainfall frequency analysis on seven sites of Sindh, Pakistan

The paper illustrates the results of regional frequency analysis of Annual Maximum Monthly Rainfall Totals (AMMRT) of seven sites of Sindh, Pakistan. The results of run test, lag-1 correlation coefficient and Mann-Whitney test have shown that the data series at given sites is random, having no serial correlation and identically distributed. The values of discordancy measure have shown that there is no discordant site in the group of seven sites. L-moments based heterogeneity measure (H) shows that the region composed of seven sites is homogeneous. The results of L-moment ratio diagram and ZDIST statistic have shown that the three distributions: GNO, PE3 and GPA are suitable candidates for regional distribution. To obtain the rainfall quantiles at ungauged sites of the study area, a linear regression model has been developed, between the mean of AMMRT of gauged sites and their respective site's elevation. The quality of the regression estimates has been tested using formal tests related to the assumptions of Classical Linear Regression Modeling (CLRM). The results have shown that the fitted model has satisfied various assumptions related to the estimation of CLRM. Hence, the estimates of this study will be useful for the estimation of rainfall quantiles of the study area for various return periods and can be utilized for the preventive measures of flood disasters, agricultural water management and the proposed improvement projects for the rehabilitation and modernization of major barrages of Indus River in the Sindh Province.

Analysis of frequency and magnitude of extreme rainfall events with potential impacts on flooding: a case study from the central United States

Climate variability and change can impact rainfall by varying time, location, magnitude, and frequency of precipitation events. Fluctuations in heavy rainfall events can impact flooding and drought events and water management systems. This research addresses temporal and spatial distributions of extreme daily and monthly rainfall in Kansas using daily rainfall data from 23 stations for the period 1890–2013. The Mann–Kendall non‐parametric method was used in trend analysis. Results indicate an increasing trend in the annual daily maximum rainfall, and an increase in the annual number of rainfall events above the 90th, 95th, and 99th percentile thresholds at a majority of stations since 1890. The most recent 30‐year climate normal period (1981–2010) was selected to assess contemporary change compared to the entire period (1890–2013). Most stations have a steeper positive slope for all extreme rainfall parameters for 1981–2010. Generally, western Kansas receives smaller and fewer extreme storms than eastern Kansas with respect to both magnitude and frequency.Since 1890, June has been the month that receives the greatest amount of rain in each year at a majority of stations (18 of 23). Stations in eastern Kansas tend to experience earlier maximum rainfall on a monthly basis than central and western stations. Earlier annual maximum monthly rains can affect soil moisture and runoff generation. Timely maintenance and improvement in water, soil, and flood management systems are necessary in order to increase preparedness of the society to flash floods and protect them from water management systems failures.

A New Method for Estimation the Regional Precipitation

In this article we propose a new method - the Most Probable Precipitation Method (MPPM) - for estimating the precipitation at regional scale. Comparisons with the Thiessen polygons methods (TPM), inverse distance weighting interpolation (IDW) and ordinary kriging (OK) on annual, monthly, seasonal and annual maximum monthly precipitation are provided. In all cases MPPM performs better than IDW and OK, and in most of them, better than TPM.

Changes to flow regime on the Niger River at Koulikoro under a changing climate

A significant decrease in mean river flow as well as shifts in flood regimes have been reported at several locations along the River Niger. These changes are the combined effect of persistent droughts, damming and increased consumption of water. Moreover, it is believed that climate change will impact on the hydrological regime of the river in the next decades and exacerbate existing problems. While decision makers and stakeholders are aware of these issues, it is hard for them to figure out what actions should be taken without a quantitative estimate of future changes. In this paper, a Soil and Water Assessment Tool (SWAT) model of the Niger River watershed at Koulikoro was successfully calibrated, then forced with the climate time series of variable length generated by nine regional climate models (RCMs) from the AMMA-ENSEMBLES experiment. The RCMs were run under the SRES A1B emissions scenario. A combination of quantile-quantile transformation and nearest-neighbour search was used to correct biases in the distributions of RCM outputs. Streamflow time series were generated for the 2026–2050 period (all nine RCMs), and for the 2051–2075 and 2076–2100 periods (three out of nine RCMs) based on the availability of RCM simulations. It was found that the quantile-quantile transformation improved the simulation of both precipitation extremes and ratio of monthly dry days/wet days. All RCMs predicted an increase in temperature and solar radiation, and a decrease in average annual relative humidity in all three future periods relative to the 1981–1989 period, but there was no consensus among them about the direction of change of annual average wind speed, precipitation and streamflow. When all model projections were averaged, mean annual precipitation was projected to decrease, while the total precipitation in the flood season (August, September, October) increased, driving the mean annual flow up by 6.9% (2026–2050), 0.9% (2051–2075) and 5.6% (2076–2100). A t-test showed that changes in multi-model annual mean flow and annual maximum monthly flow between all four periods were not statistically significant at the 95% confidence level.

Variations of annual and seasonal runoff in Guangdong Province, south China: spatiotemporal patterns and possible causes

In this study, we thoroughly analyzed spatial and temporal distributions of runoff and their relation with precipitation changes based on monthly runoff dataset at 25 hydrological stations and monthly precipitation at 127 stations in Guangdong Province, south China. Trends of the runoff and precipitation are detected using Mann–Kendall trend test technique. Correlations between runoff and precipitation are tested using Spearman’s and Pearson’s correlation coefficients. The results indicate that: (1) annual maximum monthly runoff is mainly in decreasing tendency and significant increasing annual minimum monthly runoff is observed in the northern and eastern Guangdong Province. In addition, annual mean runoff is observed to be increasing at the stations located in the West and North Rivers and the coastal region; (2) analysis of seasonal runoff variations indicates increasing runoff in spring, autumn and winter. Wherein, significant increase of runoff is found at 8 stations and only 3 stations are dominated by decreasing runoff in winter; (3) runoff changes of the Guangdong Province are mainly the results of precipitation changes. The Guangdong Province is wetter in winter, spring and autumn. Summer is coming to be drier as reflected by decreasing runoff in the season; (4) both precipitation change and water reservoirs also play important roles in the increasing of annual minimum monthly streamflow. Seasonal shifts of runoff variations may pose new challenges for the water resources management under the influences of climate changes and intensifying human activities.

Impact of two low ozone events on surface solar UV radiation over the northeast of Spain

AbstractTotal ozone column (TOC) abundance over northeastern Spain follows a strong seasonal pattern with higher values in spring and lower values in fall. The annual cycle has weakened since the late 1970s, due to a decrease in the ozone annual maximum monthly mean in spring. The long‐term trend and the seasonal variability of the TOC suggest that thresholds of ozone ‘mini‐holes’ should be defined as deviations from local monthly mean levels. Ozone mini‐holes are synoptic scale regions of short‐term, large TOC reductions. The climatology of ozone mini‐holes over Barcelona shows a seasonal pattern, with a higher frequency in winter and early spring. Nevertheless, many of these events are detected in September, when the UV irradiance reaching the Earth's surface is still high. This may enhance negative effects such as erythema.The deepest ozone ‘mini‐hole’ ever reported over the area was on 10 January 2004, when the daily TOC was about 40% lower than the climatological mean for January. A high‐pressure system induced cloud‐free skies, and the small temporal variations in aerosol concentrations indicated that low TOC was responsible for the enhanced UV radiation at ground level: the erythemal irradiance at noon was 36% higher than the day before. However, in absolute terms, this increase is relatively small as UV levels in winter are low. Nevertheless, the low ozone events observed in late spring could be biologically harmful, even though the TOC anomaly was rather less than the winter values. On 20 April 2004, low TOC and high solar elevation favoured the increase that was detected in UVB radiation, especially at shorter wavelengths. The UV Index at noon was 1 unit higher than the previous day's value, due to an uplift of the tropopause and a reduction in the ozone mixing ratio in the upper troposphere–lower stratosphere (UTLS) region. Copyright © 2010 Royal Meteorological Society

Characteristics of the Largest Recorded Annual Maximum Monthly Precipitation in an Atmospheric Global Climate Model Experiment

本研究では，大気全球気候モデル（AGCM）の長期積分結果を用いて，数値実験で再現された既往最大月降水量が，観測をどの程度再現し，またどのような統計的性質を持つかを調査した．AGCMから得られた既往最大月降水量の再現期間は，統計学的には何ら地理的分布を示さなくてよいが，ある地域では500（50）年を上（下）回る再現期間が現れるという特徴的な地理分布を示し，全球で再現期間を集計した確率分布関数は，モデル値と理論値とで良く一致したが，観測値とは定量的には一致しなかった．また，既往最大月降水量を10位の年最大月降水量で割った値（極値比）は，再現期間と同様，地域分布が見られ，極端に大きい月降水量が生じる地域は決まっていることが示された．400年以上の再現期間を持つ年最大月降水量が推定される原因を調べたところ，極値比が大きい （小さい）と，極値統計の一手法であるLモーメント法の3次モーメント（L-skewness）と4次モーメント（L-kurtosis）が共に大きい（小さい）分布となり，極値比と分布形の二つの要素に原因があることが示された．これらの結果は，AGCMで再現された既往最大値を含む極値を水文・水資源の研究に利用する際，十分な注意が必要であることを示唆している．

Estudo para Identificação de Tendências do Regime Pluvial na Região Metropolitana de Belo Horizonte a Partir de Métodos Estatísticos

Water resources systems are usually designed under the assumption of statistically stationary time series of precipitation and/or streamflow. However, this assumption must be previously verified if changes in climate and land use are issues of interest. In these cases, designs based on the assumption of stationary hydrologic time series should be revised, with the specific aim of verifying the possible impacts that these changes would have on the local water infrastructure. In this context, potentiated by intense controversies about climate change, this paper describes a collection of parametric and non-parametric statistical tests for detecting possible trends in the rainfall regime of the Metropolitan Region of Belo Horizonte, in southeastern Brazil. For this analysis data from 20 gauges, with 50 to 149-year series were collected in four groups of rainfall series: the annual rainfall series, the quarterly rainfall series, the halfyearly series and the annual maximum monthly rainfall series. Prior to the use of statistical tests, the 4 groups of precipitation series were submitted to a preliminary graphical analysis covering time series plots of a 10-year moving average and moving median, LOWESS smoothing (Locally Weighted Scatterplot Smoothing), linear regression and RAPS (Rescaled Adjusted Partial Sums) graphs, as well as an exploratory analysis for detecting and identifying possible trends and/or abrupt changes in data. After this graphical and exploratory study, the data were formally analyzed using TREND software, developed by the Australian Cooperative Research Center for Catchment Hydrology (CRCCH), aiming to identify possible trends or abrupt changes in point precipitation series within the region

ESTIMATION OF THE FREQUENCY ANALYSIS OF ANNUAL MAXIMUM MONTHLY PRECIPITATION IN EAST ASIA BASED ON A DYNAMICAL ENSEMBLE METHOD

The present paper investigates the estimation of the frequency analysis of the annual maximum monthly precipitation (AMMP) in East Asia based on a dynamical ensemble approach with an atmospheric global climate model. The model used is the latest version of the MRI/JMA 98 with about 300-km horizontal resolution with 30 vertical layers. 130-year integration was performed with the ensemble size of six. Two formulation of the frequency analysis for the ensemble dataset are first introduced: ensemble mean and composite estimators. The estimation of the AMMP for 50-and 200-year retrun period from the comoposite model outputs basically reproduces that of the observation. Further analysis demonstrates that each member of the ensemble can be combine into one based on the statical F-test and that natural variablity significantly affect the estimation error of the extreme values.

Connectivity between Eurasian snow cover extent and Canadian snow water equivalent and river discharge

We explore pan‐Arctic climate connectivity by examining historical time series of satellite‐based measurements of Eurasian snow cover extent and of observed Canadian snow water equivalent (SWE) and freshwater discharge, with a focus on the Churchill River Basin of Labrador and the Chesterfield Inlet Basin of Nunavut. Analysis of the data reveals statistically significant positive (negative) correlations between spring and summer Eurasian standardized snow cover extent anomalies and annual maximum monthly SWE as well as freshwater discharge in the Churchill River (Chesterfield Inlet) Basin the following year. A spatially coherent response to the forcing is observed since 19 rivers draining more than 0.6 × 106 km2 of northern Quebec and Labrador and with a mean annual total discharge of 320 km3 yr−1 show statistically significant positive correlations to the annual Eurasian standardized snow cover extent anomalies. The origin of this pan‐Arctic climate connectivity is related to the persistent nature of the Eurasian snow cover extent anomalies and the associated accumulated gains or deficits in the surface radiation and water budgets that impose a memory in the climate system. The Eurasian snow cover extent anomalies provide some degree of predictability (up to 1 year in advance) of the surface water budget in the Churchill River and Chesterfield Inlet Basins. They further suggest that a declining trend in Eurasian snow cover extent will yield decreasing (increasing) SWE and river discharge in the Churchill River (Chesterfield Inlet) Basin in the 21st century.

Coral bleaching and elevated sea-water temperature in Milne Bay Province, Papua New Guinea, 1996

A coral bleaching event began in February 1996 on reefs in Milne Bay Province, Papua New Guinea. Corals were affected on the shallow fringing reef and to water depths of greater than 20 m on the reef slope. Bleaching was extensive and in the survey area 54% of all corals were bleached. Branching corals (particularly Acropora and Pocillopora) were more severely affected than massive species. Bleaching occurred at the time of the annual maximum monthly sea temperature when long-term sea temperature data sets recorded an anomaly of + 1.29°C. Analysis of the anomalies over the previous 40 years shows a positive trend of 0.09°C per decade.

Spectral ultraviolet‐B radiation fluxes at the Earth's surface: Long‐term variations at 39°N, 77°W

Precision Measurements of UVB global irradiance in 5‐nm‐wide spectral bands centered from 290 to 320 nm were made continuously from September 1975 through December 1990. The spectral radiometer was calibrated at roughly monthly intervals. Annual maximum monthly means for total daily radiation, radiation at solar noon, and clear sky radiation at small secants all were observed to be significantly higher during the period from 1983 through 1989. The maximum monthly mean of integrated 295–320 nm total daily radiation in 1986 was 29% above the long‐term mean, 47% above the maximum in 1982, and 54% above the mean maxima for 1979–1982. These interannual changes were largest for the shorter wavelengths but were significant for all spectral bands. Interannual variations in clear sky radiation were largest at small secants. For maximum monthly means of integrated 295–320 nm flux, the secant 1.2 maximum in 1989 was 19% above the long‐term mean and the average of the maxima during 1983–1989 was 13% above the long‐term mean.