Spatial and temporal analysis of rainfall concentration over the Mediterranean according to two different indices

Shifa Mathbout, JA Lopez-Bustins, D Royé and J Martin-Vide

16tth EGU-Plinius conference on Mediterranean risks, Montpellier, France, 9-12 October. 2018, Montpellier, France, 9-12 October. 2018October. 2018October

Climate analysis for the Mediterranean as a whole is

difficult due to the spatial complexity of this region in

addition to the dynamical and physical atmospheric

processes complexities observed in this region.

The precipitation seasonality in the MR is considered

one of the main factors which affect the terrestrial and

aquatic ecosystems and the human development

Mean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual Precipitation1961

Mean Annual PrecipitationMean Annual PrecipitationMean Annual Precipitation19611961-

Mean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual PrecipitationMean Annual Precipitation19611961-2006

01002004006001,0001,400 mm

National Geophysical Data Centre (NGDC)

What is the objective of this study?

The main objective of this research is to provide an overview about

the approximate spatial and temporal distribution of the

precipitation concentration over the Mediterranean according to

two important indices.This presentation is a part of another scientific work whichwere presened in EGU , 2018 and is ready to submit in theInternational Journal of Climatology and speaks about the

relation of precipiation concentration and seventeleconnection patterns

For a better spatial coverage of the Mediterranean region

Daily Global Historical Climatology Network (GHCN-Daily) dataset was also used.

Daily data of the European Climate Assessment & Dataset (ECA&D) has been used

Unpublished data has been obtained by contacting the regional National

Hydrological and Meteorological Services.

The original series of daily precipitation data were completely

controlled and reconstructed using the R package RClimdex which

allows for checking duplicate dates, internal coherence, rounding

problems and outliers. For each year, the number of missing values

was calculated and if it was less than 5% of the total values, the time

series was considered suitable for subsequent analysis.

The outliers that lay outside 4 standard deviations of the mean

value of each time series were excluded. As a result, 233 out of

the 330 available rainfall series for 1975–2015 were used for

analysis, except some stations in Syria (till 2012).

233 daily series are considered for this study during

(1975-2015)

1- Daily Precipitation Concentration Index CI (Martin-Vide ,2004)

The CI index method consists of aggregating daily precipitation events

after sorting all rainfall values from the minimum to the maximum to

assess the contribution of the largest daily event to the total amount .

0

20

40

60

80

100

0 20 40 60 80 100

Rela

tive

cum

mul

ativ

e pre

cipi

tatio

n

Relative cummulitave number of rainy days

SA

Ordered version of the n index (𝒏𝒐𝒓) (Monjo,2016)

• The 𝒏𝒐𝒓 index is an ordered n index has been defined using

the maximum average intensities (MAI) depending on the

ordered daily precipitation values .

Calculation of CI and 𝑛𝑜𝑟, and all statistical analysis were

carried out t in the R (3.2.2) statistical environment (R Core

Development Team, 2016), including ggplot2 for the graphics.

Main Results:

General characteristics of the precipitation over the Mediterranean basin during 1975 - 2015.

Spatial distributions of the mean number of wet days(pp>0 mm) over the Mediterranean in 1975–2015.

Spatial distribution of daily precipitation concentration across the Mediterranean during 1975-2015

1- CI Index Distribution

𝑛𝑜𝑟

2- 𝐧𝐨𝐫 Index Distribution

Trends in the annual precipitation concentration CI and 𝑛𝑜𝑟 .Statistically significant (95% confidence level)

CI Index

𝑛𝑜𝑟 Index

A unique trend cannot be detected; however, trend analysis demonstrated mostly increasing trends for both indices

(at approximately 61%) were Significant at 95% confidence level) at 28% of total stations, which reflect, in general, a clear tendency

toward a higher seasonality of the rainfall distribution.

Main Conclusions

Strong spatial connections were found between CI and 𝑛𝑜𝑟 andboth indices have showed coherent and similar behavior whichpresented the same relative areas of high and lowconcentration.

The high to moderate irregularity and rainfall concentration arethe two very characteristic features of rainfall in theMediterranean basin and the higher values for both indiceswere detected in the western parts of the Mediterranean alongthe east Spanish and south east French coasts, Sicily in SouthItaly.

A clear spatial difference in the rainfall concentration betweenwestern and eastern parts of the Mediterranean was evident. Theannual values range from 0.49 to 0.70 for CI and 0.43 to 0.65 fornor index

High levels of temporal variability in the daily precipitationconcentration values were evident in eastern parts of theMediterranean, and Morocco as well indicating a high variabilityof precipitation on interannual time scale across the MRparticularly in the arid areas of the Eastern Mediterranean.

Latitude and the distance from the Atlantic ocean might be themost important variables that affect the spatial distribution andvariations in daily precipitation concentration which was moreevident according to CI.

Rain can be seen as both the giver and the taker of life.