Data availability and quality

The forty one weather stations selected for the record analysis used in this study

(rainfall and dust events), identifiers and characteristics are indicated in table 4 such as:

number of station in the work, station code, station name, province: LP (Las Palmas) and

TF (Sta. Cruz de Tenerife), acronym used in the study, station elevation in m., location,

geographical coordinates in sexagesimal format, period, number of years considered in

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Table 4. Weather stations selected for the analysis of all the records used in this study. N (number of station in the work), Ind. (station code), St. Name (station name), Prov. (province: LP (Las Palmas) and TF (Sta. Cruz de Tenerife)), Acr. (Acronym used in the study), Elev. (station elevation in m), Loc. (location), geographical coordinates (Lat.N and Log.W: latitude North and longitude W respectively in sexagesimal format), Period, N.yr (number of years considered in the data analysis) and Obs. (type of observation: D (daily) or/and H (hourly)).

N Ind. St. name Prov. Acr. Elev.(m) Loc. Lat.N Long.W Period N.yr. Obs.

1 C649I G. Can. A. LP A1 24 E 27 55 21 15 23 22 1951-2012 62 D/H 2 C029O Lanz. A. LP A2 14 SE 28 57 07 13 36 01 1972-2012 41 D/H 3 C249I Fuert. A. LP A3 25 E 28 26 41 13 51 47 1969-2012 46 D/H 4 C447A Ten. N. A. TF A4 632 NE 28 28 39 16 19 46 1960-2012 62 D/H 5 C429I Ten. S. A. TF A5 64 S 28 02 51 16 33 39 1980-2012 33 D/H 6 C139E La Palma A TF A6 33 E 28 37 59 17 45 18 1970-2012 43 D/H 7 C929I El Hierro A. TF A7 32 NE 27 49 08 17 53 20 1973-2012 40 D/H 8 C689E Masp. LP P1 6 SW 27 44 08 15 35 53 1997-2012 16 D 9 C656U Teror Dom. LP P2 630 N 28 03 59 15 32 38 1963-2012 50 D 10 C662I Valleseco R. LP P3 1400 N 28 01 44 15 36 12 1965-2012 48 D 11 C654Q S. Mat. Lag. LP P4 1160 C 28 00 18 15 34 49 1965-2012 48 D 12 C626E Mogán B A. LP P5 715 SW 27 53 35 15 40 45 1964-2012 49 D 13 C624E Tejeda V.Ñ. LP P6 1040 C 27 55 55 15 40 30 1964-2010 47 D 14 C637A S.B. Tir. P. LP P7 570 S 27 50 20 15 38 10 1965-2012 48 D 15 C625O S.B.Tir.L.P.A. LP P8 806 S 27 51 24 15 38 41 1965-2012 48 D 16 C625A Mogán Inag. LP P9 950 W 27 55 52 15 4415 1952-2010 59 D 17 C627A S. Nic. T.T. LP P10 420 SW 27 55 12 15 45 47 1965-2009 45 D 18 C669A Arucas Bañ. LP P11 50 N 28 08 47 15 32 01 1965-2012 48 D 19 C647O Valseq. G.R. LP P12 540 C 27 59 30 15 29 38 1965-2012 48 D 20 C665L Moya Font. C. LP P13 950 N 28 03 25 15 36 15 1965-2012 48 D 21 C659Q L. Canteras LP P14 15 N 28 08 26 15 26 02 1965-2012 48 D 22 L. Alhorr. LP P15 1100 C 27 59 57 15 33 13 1924-2012 89 D 23 C649U Telde - LL. LP P16 150 E 27 59 43 15 25 09 1965-2012 48 D 24 C449C S.C. Ten. TF T1 35 NE 28 27 47 16 1519 1960-2012 62 D 25 C469A S.J. Rambla TF T2 106 N 28 23 38 16 39 02 1948-2012 62 D 26 C129C Tazac. M.T. TF T3 274 W 28 36 42 17 54 54 1984-2012 29 D 27 C457C Tacoronte TF T4 564 NE 28 28 55 16 24 35 1945-2012 62 D 28 C430E Izaña TF T5 2371 C 28 18 32 16 29 58 1933-2012 62 D 29 C419X Adeje Cal. B TF T6 130 SW 28 04 53 16 42 39 1988-2011 23 D

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N Ind. St. name Prov. Acr. Elev.(m) Loc. Lat.N Long.W Period N.yr. Obs.

30 C126A El Paso C.F. TF T7 844 W 28 39 14 17 51 11 1986-2012 27 D 31 C117A Puntagorda TF T8 684 NW 28 45 38 17 59 08 1986-2012 27 D 32 C329Z S. S. Gomera TF T9 15 E 28 05 23 17 06 41 1995-2012 18 D 33 C317B Agulo J.B. TF T10 765 NW 28 10 44 17 12 47 1986-2012 27 D 34 C315P Valleher. Ch. TF T11 1242 W 28 06 38 17 15 47 1986-2012 27 D 35 C427E S. M. Abona TF T12 642 S 28 05 48 16 36 57 1952-2012 61 D 36 C128B Ll. Arid. B TF T13 410 W 28 39 32 17 54 37 1978-2012 35 D 37 C127U Fuenc. Cal. TF T14 498 S 28 29 42 17 49 43 1946-2012 67 D 38 C939U Sabinosa TF T15 299 W 27 44 51 18 05 45 1978-2012 35 D 39 Berm. A. BER1 7 NE 32 21 50 64 40 01 1949-2011 63 D 40 505 Horta Obs. Az. 45 SE 38 31 16 28 42 50 1970-2011 42 D 41 522 Funch. Obs. M 58 S 32 38 51 16 5 333 1970-2011 42 D

Some abbreviations used for the weather stations are: A. (Airport), Obs.

(observatorio) G.Can. (Gran Canaria), Fuert. (Fuerteventura), Lanz. (Lanzarote), Ten. N.

(Tenerife Norte), Ten. S. (Tenerife Sur aeropuerto), Masp. (Maspalomas), Teror Dom.

(Teror-Dominicas), Valleseco R. (Valleseco-La Retamilla), S. Mat. Lag. (San Mateo-Las

Lagunetas), Mogán B. A. (Mogán- Barranquillo Andrés), Tejeda V. Ñ. (Tejeda-Vivero

de Ñameritas), S.B. Tir. P. (San Bartolomé de Tirajana-Palomas), S.B. Tir. L.P.A. (San

Bartolomé de Tirajana-Lomo Pedro Alfonso), Mogán Inag. (Mogán (Inagua)), S. Nic.

T.T. (San Nicolás de Tolentino-Tasarte), Arucas Bañ. (Arucas (Bañaderos)), Valseq.

G.R. (Valsequillo-Granja Las Rosas), Moya Font. C. (Moya-Fontanales Cisterna), L.

Canteras (Las Palmas de G.C.-Las Canteras), L. Alhorr. (Lomo Alhorradero), Telde-LL.

(Telde Los Llanos), S.C. Ten. (Santa Cruz de Tenerife), S.J. Rambla (San Juan de La

Rambla), Tazac. M.T. (Tazacorte-Mña Todoque), Adeje Cal. B (Adeje-Caldera B), S. S.

Gomera (San Sebastián de La Gomera), Agulo J.B. (Agulo-Juego Bolas), Valleher. Ch.

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de Aridane B), Fuenc. Cal. (Fuencaliente-Caletas), Berm. (Bermuda) and Funch.

(Funchal).

These points have been selected due to their geographical position, altitude and

orientation. These factors contribute in explaining the rainfall regimen affecting the

studied area. Even though the coverage of time varies between stations, the average

recording period, around 48 years, is considered suitable for the purpose of this study. It

should be taken into account that this period can change according to the objective of the

investigation as will be explained in the result section. The comparison between the

conclusions extracted from the analysis of the different stations must be in some cases

interpreted cautiously because of the absence of a whole common period for all the

analysis made.

Due to the absence of orographic effects in Bermuda, an advantage in the analysis

of the rainfall is to consider a single station as representative of the entire archipelago.

Although some other stations are currently being operated in Bermuda, (Commissioner's

P., St. David's and F. Prospect) the time series records are quite short to be compared with

the rest of the observations sets.

However, for the rest of the sites within this subtropical region, the practical

limitation when analysing data from many stations has been found. The rainfall data

availability for the Canary Islands in AEMET is shown in Fig.14 as the distribution of the

rainfall Time series in La Palma (LPa), La Gomera (G), El Hierro (EH), Tenerife (Ten),

Gran Canaria (GC) Lanzarote (Lz) and Fuerteventura (Fv) throughout the number of

years of measurements. In light blue is shown for periods of 0 to less than 30 years and

in dark blue for periods equal or more than 30 years (Fig.14a) or equal to 30 years

(Fig.14b). The rainfall data coverages for the periods 1951-2012 and 1981-2010 are

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14b). The percentage of the number of stations according to its quality can be found at

the bottom (Fig.14c).

Fig. 14. Distribution of the rainfall Time series in La Palma (LPa ), La Gomera (G) , El Hierro ( EH), Tenerife (Ten), Gran Canaria (GC) Lanzarote (Lz) and Fuerteventura (Fv ) through the number of years. (a) Rainfall data coverage for the period 1951-2012. Light blue for 0 to less than 30 years and dark blue for 30 or more years. (b) Rainfall data coverage for the period 1981-2010. Light blue for 0 to less than 30 years and dark blue for 30 years. (c) The percentage of the number of station according to its quality.

The selection of the weather stations for most of the analysis made in this work

responds to the availability of Time series of 30 years of high quality.

High quality or 100% of valid data is considered when the time series have not

gaps or a -4 coded value on a specific date. The -4 code value means that no rainfall

amounts were register on this date, and is being accumulated towards the next registered

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at medium or high altitudes because they are not easy to reach to make the observations.

Negligible rainfall, less than 1mm is coded by -3 and corresponds to a value less than 0.1

mm. In this work such values have been computed as 0.05 mm.

The largest number of the stations with rainfall measurements during 30

consecutive years in the period 1981-2010 is in Gran Canaria (GC), a percentage of

34.4%, followed by the most eastern islands with 14.3%, the most western ones with 7 %

and Tenerife with 6.6 % (Fig.14b). Moreover, the highest percentage of valid data (80%)

is found in Gran Canaria (Fig.14c) .This is one of the reasons, apart from its central

location in the archipelago, why the rainfall trend in Gran Canaria has been deeply

studied.

In Annexe I, table A shows the statistical of data availability with a percentage

higher than 95% from the weather stations within AEMET during the period 1981-2010

in La Palma (LPa), La Gomera (G) and El Hierro (EH); table B in Tenerife (Ten), table

C in Gran Canaria (GC) and table D in Lanzarote (Lz) and Fuerteventura (Fv). These 4

tables include the code of each station (Ind.), the station name (St.name), the orientation

(North N (1) /South S (2)) , the elevation in m (Elev.(m), the latitude in degrees

(Lat.(deg.)), the longitude in degrees (Lon.(deg.)), the number of dates with -4 (N(-4)),

the number of dates with negligible rainfall (N(-3)), the number of zeros (N(0)), the

number of values higher than zero (N(>0)), the number of data coded by -9999 or not data

(N(-9999)), the number of blank spaces or no data (N (B)), the number of real data (N R),

the percentage of data (data %), the initial year (Ini.yr.), the last year (Last yr.) and the

total number of years (N.yrs.).

For Madeira, data from the Funchal Obs (M) were considered because of its

appropriate length. Data from the Horta Obs. (Az) were also chosen because it serves as

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Weather Forecasts). Several problems like data homogeneity, changes in instrumentation

and the lack of long time series should be considered in the interpretation of the results

obtained from this analysis. The worst quality of the rainfall measurements is usually

found in the rainiest locations where the gaps are frequent or the accumulation of several

rainfall days is registered in one single day. This practice hinders the analysis of the daily

rainfall data which could be very interesting in detecting the extreme events.