Liana abundance and diversity increase with rainfall. Us dept of commerce national oceanic and atmospheric administration national weather service wakefield, va 9 general mahone highway wakefield, va 23888. Rainfall seasonality index and individual seasonality index values were calculated, and trend analysis was performed on yearly data for the individual seasonality index, using the mannkendall test, the sequential mannkendall test and sens slope method also known as the theilsen estimator. The assumption is made that mean monthly rainfall totals for a location are vector quantities, magnitude being the amount of rain, and direction being the month expressed in units of arc.
In the case of using an index some transformations are needed. Changes in the seasonality of precipitation over the. Jun 01, 2015 two new indicators of rainfall seasonality based on information entropy, the relative entropy re and the dimensionless seasonality index dsi, together with the mean annual rainfall, are evaluated on a global scale for recently updated precipitation gridded datasets and for historical simulations from coupled atmosphereocean general circulation models. Analysis of rainfall seasonality from observations and climate models. Sep 01, 20 this paper examined rainfall seasonality in the niger delta, nigeria, using both monthly and annual rainfall data from 1931 to 1997. Precipitation regimes and associated seasonality index values are documented by walsh and lawler 1981 are provided in table 2. We are examining the rainfall seasonality of a monthly time series of rainfall, which measures how one month in a given year rainfall differs than if each month received 112 of the annual rainfall. Seasonality index helps in identifying the rainfall regimes based on the monthly distribution of rainfall. In an attempt to quantify these contrasts, the seasonality index st was developed, which is simply the sum of the absolute deviations of mean monthly rainfalls from the overall monthly mean, divided by the mean annual rainfall. Pdf individual seasonality index of rainfall regimes in.
Trend analysis using linear regression during these. Spatial trends in rainfall seasonality royal meteorological society. The strong response of lianas to the normalized seasonality index indicates that, in addition to. Fossil proxies which can be related directly to rainfall seasonality have the potential to assist in quantifying these shifts. Recent citations impact of rainfall seasonality on intraspecific trait variation in a shrub from a. The bigger the difference the more the seasonality. The statistical theoretic normal value for each season is 25%. In the past, several methods have been used to analyze trends in seasonality of precipitation characteristics. Analysis of rainfall seasonality index in iraq hasanain k. Seasonality of precipitation in the united states jstor. Assessment of seasonal and annual rainfall trends and. The present study is based on data from monthly rainfall recorded in the period 1945 to 2005 in a total of 225 raingauge stations spread all over region.
Pdf individual seasonality index of rainfall regimes in greece. Oct 17, 2019 the normalized seasonality index is defined as the product of the entropy of the monthly rainfall distribution relative to a uniform distribution and the annual rainfall normalized by the maximum annual rainfall across all sites feng et al. Jan 25, 2019 the index amount represents a decimal fraction indicating the ratio of a period amount to the average of all periods. Pdf analysis of rainfall seasonality from observations and. Spatial and trend analyses of rainfall seasonality and erosi. Two new indicators of rainfall seasonality based on information entropy, the relative entropy re and the dimensionless seasonality index dsi, together with the mean annual rainfall, are evaluated on a global scale for recently updated precipitation gridded datasets and for historical simulations from coupled atmosphereocean general circulation models. Rainfall variability and seasonality in northern bangladesh. Although a few studies on rainfall spatial and temporal variability in the uae have been carried out, evidence of the impact of climate change on rainfall trends has not been reported. The predictability index for the highest total precipitation within the area. Get daily timeseries of us station data and others. For each disease, a monthly seasonality index was applied to describe both overall and regional variations in seasonal patterns. The insets show qualitative differences in the monthly rainfall distribution between. Insignificant trends in monthly precipitation were also described by. Peac seasonal rainfall forecast national weather service.
The data was retrieved from the archives of the nigerian meteorological. As with rainfall concentration, the seasonality of rainfall is best determined by the socalled markham technique. Jul 25, 2019 where r i is the total annual rainfall for the particular year under study. Rainfall behavior seasonality and time trends in the average monthly rainfall in major cities of nigeria olaoluwa s.
The peac seasonal rainfall outlook is an experimental consenus forecast, produced monthly for 14 stations within hawaii and the usapi. The peac outlook uses data from the following 7 models. Individual seasonality index of rainfall regimes in greece. The variation in seasonality in rainfall over the indian region is examined using monthly rainfall values for the period 1951 to 2015 of 34 meteorological subdivisions excluding two sea islands. Using the seasonal and temporal precipitation concentration index for characterizing the monthly rainfall distribution in spain. Annual rainfall seasonality is an index derived from two ratios. For locations with very low rainfall or during dry season periods, anomalies can take extreme values. Pdf changes in rainfall seasonality in the tropics scinapse. Changes in rainfall seasonality pattern over india rai. S is shown for stations in the ghcnmonthly data set as a function of normalized mean annual rainfall.
Individual seasonality index of rainfall regimes in greece article pdf available in climate research 282. S is shown for stations in the ghcn monthly data set as a function of normalized mean annual rainfall. If season rainfalltotal rainfall % or monthly rainfalltotal rainfall % are used then calculations are very simple. Akomolafe3 several features may be present in rainfall data, and sophisticated time series procedures are needed for the analysis. Analysis of rainfall seasonality from observations and. Other methods are based on estimation of linear trends in precipi. Trend analysis results show no significant change in the seasonality of rainfall in this. Rappaport, 2000, particularly in coastal regions xu et al. Rainfall seasonality index is a critical environmental factor affecting the evolution of natural vegetation. May 18, 2016 the mean individual seasonality index 0. Storm surge, heavy rainfall, and flooding resulting from tropical cyclones tcs can cause tremendous damages e.
Seasonal historical rainfall south florida water management. When monthly figures are added vectorially, the resultant can be used to compute a seasonality index, which is the ratio of the magnitude of the. Using the seasonal and temporal precipitation concentration index. Additional analyses of the seasonality index this section presents additional analyses of the seasonality index and its trends over the past century using monthly rainfall data from stations in highly seasonal regions supplementary figure s1 as well as monthly gridded data over the entire tropics supplementary figures s2 and s3.
This means that january is about 76 percent of the average. For example, the pages can plot variables for years where the pna index was high. How calculate the seasonal index, deasonalise data, convert deseasonalised and actual data back. They discovered that seasonality is low in equatorial areas but increases rapidly with latitude, particularly towards the sahara where the highest seasonality index s. Trends and variability of monthly, seasonal and annual. Some of these methods are based on estimation of seasonality index from mean monthly rainfall and mean annual rainfall walsh and lawler, 1981. Kanellopoulou 2002, which is a function of mean monthly and annual rainfall, is computed using the following formula. Changes in seasonality index over subdivisions of india during. Data required for the calculation of the rainfall seasonality index are.
Ukmo, nasa gmao, ecmwf, iri, ncep constructed analog, ncep coupled model and apcc mme. Changes in rainfall pattern and seasonality index 641 table 2. Pdf rainfall seasonality in the niger delta belt, nigeria. The tc data were collected from the shanghai typhoon institute of the china meteorological administration. The ratio of cool to warm season rainfall totals plus 1 are assigned negative values when rainfall in the cool. Monthly climate timeseries noaa earth system research. The quality of data set was firmly controlled before its release and was organized by attributes such as date, latitude, longitude, tc number, landfalling region, tc center pressure, and intensity the maximum sustained wind from 1949 zhang et al. It was found that the length of the dry period is lower at the northeastern part of northern bangladesh. Rainfall seasonality captured in micromammalian fauna in late. If season rainfall total rainfall % or monthly rainfall total rainfall % are used then calculations are very simple.
Long memory, seasonality and time trends in the average monthly rainfall in major cities of nigeria olaoluwa s. Spatial and trend analyses of rainfall seasonality and. The variable r i is the total annual precipitation in a particular year, and x in is the actual monthly rainfall in month n. Changes in the seasonality of precipitation over the contiguous usa s. Ukmo, nasa gmao, ecmwf, iri, ncep constructed analog, ncep coupled model and. The data was retrieved from the archives of the nigerian meteorological agency in lagos.
Walsh and lawler 1981 linked rainfall seasonality in africa, to latitude. Precipitation seasonality and variability over the tibetan. The probabilistic interpretation of the monthly rainfall fractions also allows us to estimate circular statics moments associated describing the annual distribution of rainfall and, in particular, the center of mass centroid of the annual precipitation, which for seasonal rainfall regimes is a measure of the. Our data has the below structure and continues monthly through water year 2014.
This plot shows ndvi values for the selected year and for a medium term average 12 years, 200220. To address these issues, this study analyzed the spatial and temporal characteristics of rainfall seasonality. Rainfall seasonality is related to the temporal distribution of rainfall on a monthly. Rainfall seasonality captured in micromammalian fauna in. The assumption is made that mean monthly rainfall totals for a location.
To delineate southern africa into regions of rainfall seasonality, the all year rainfall region was first identified, by analysing the median i. The impact of tcs on extreme rainfall has been investigated by dare et al. This paper examined rainfall seasonality in the niger delta, nigeria, using both monthly and annual rainfall data from 1931 to 1997. Relationships between mean monthly temperature and mean monthly rainfall in modern environments are quantified to generate a seasonality index associated with summer or. Seasonality index s d rrmax figure 1 jseasonality index in the tropics. Relationships between mean monthly temperature and mean monthly rainfall in modern environments are quantified to generate a seasonality index associated with summer or winter rainfall. Though this index can only provide a very simple description of the seasonality pattern, it can be a very useful tool with which to study spatial and temporal seasonality variations sumner et al. The changes in the seasonality index are noticed almost all the district of maharashtra. Changes in seasonality index over subdivisions of india. Highresolution monthly rainfall database for ethiopia. Map and the variability of monthly rainfall throughout the year, was a significant predictor of both liana density and species richness, whereas map, rainfall seasonality and the mean dry season precipitation mdp were far weaker predictors. Effects of global warming and solar geoengineering on. Nonstationarity in seasonality of extreme precipitation. An equal distribution would assign approximately 8% to each month.
Rainfall seasonality can be estimated by the walsh and lawler 1981 index. Mar 14, 2019 despite the importance of seasonal distribution and interannual variability of rainfall to the ecosystem and society, there is a lack of regionallevel studies on rainfall seasonality, and teleconnections between global climate events and rainfall seasonality are not well understood. Rainfall seasonality over india is studied using an individual seasonality index. How to use microsoft excel to calculate seasonal indexes. Long memory, seasonality and time trends in the average. Monthly rainfall analysis national weather service.
Monthly seasonal composites monthly seasonal correlation daily timeseries daily teleconnection plots and forecasts. Detecting changes in rainfall pattern and seasonality. Rainfall seasonality in the niger delta belt, nigeria. In this study, the characteristics and basic features of precipitation on the tp during an 11yr period 200111 are described on monthlytoannual time scales.
The rift valley and adjoining highlands receive much of the rainfall during jjas, which accounts for 30%60% of rainfall variability, and secondary rainfall during mam, which accounts for 20. The ratio of warm octnovdecjanfebmar to cool aprmayjunjulaugsep season rainfall totals minus 1 are assigned positive values when rainfall in the warm season is greater than rainfall in the cool season. The rainfall seasonality index is used to study the spatial and temporal change in rainfall behavior in that contribute in improvement of water and management plans of water resources systems and agriculture in a certain region especially during dry seasons. The data was collected on 9 synoptic stations in the region.
To create overall monthly seasonality indices for each disease, the studyspecific monthly proportions were. The spatial distribution of the individual seasonality index and the mean individual seasonality index over two periods, that is, early 19011970 and recent 19712015, is analysed. Detecting changes in rainfall pattern and seasonality index. Data and methodology monthly rainfall data of around 335 raingauge stations of the state maharashtra for the period 1901 to 2006 are collected from national data centre of india meteorological department, pune.
May 14, 20 because of the scarcity of meteorological observations, the precipitation climate on the tibetan plateau and surrounding regions tp has been insufficiently documented so far. The index amount represents a decimal fraction indicating the ratio of a period amount to the average of all periods. Projected changes of rainfall seasonality and dry spells. Using the seasonal and temporal precipitation concentration. The statistical tools employed for the study are the cumulative index analysis and the percentage of mean. The remaining variability of the monthly rainfall is due to rainfalls in the other months as these regions get rainfall throughout nearly the whole year. This study aims at assessing the significance of longterm rainfall trends and temporal variability at sharjah city, uae.