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Definitions and basicconcepts

The Aridity index (1) can be estimated by the Bagnouls-Gaussen index (BGI) using the following equation:nBGI = S (2ti - Pi)*k

i=1where: ti is the mean air temperature for month i in 0C, Pi is the total precipitation for month i in mm; and krepresents the proportion of month during which 2ti - Pi >0.

Aridity index can be also defined as the ratio between mean annual precipitation (P) and mean annualevapotranspiration- (ETP) calculated with the Penman formula.

Benchmarks Indication ofthe values/ranges of value

The aridity index defined as the ratio P/ETP has been proposed by the UNCCD to identify areas prone to using thefollowing three classes:

>0.65 - humid

0.5-0.65- dry

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indicators

CLIMATE:

Madagascar has a tropical maritime climate which is influenced by altitude, the monsoons and its proximity to the sea. In general,the highlands have a temperate climate with warm rainy weather from November to April and cooler temperatures from May to October. The

average annual precipitation varies from 1,000 to 1,500 mm (39 to 59 inches). The coastal region has a tropical climate with no completely dry

season. The heaviest rainfall occurs on the coastal region between May and September with average annual precipitation varying from 2,030mm to 3,250 mm (80 to 120 inches).

Average temperature ranges in Antananarivo are from 9 to 20 degrees Celsius (48 to 68 degrees Fahrenheit) in July to 16 to 27 degrees Celsius(61 to 81 degrees Fahrenheit) in December.

Month

Mean Temperature

CMean Total Rainfall (mm) Mean Number of Rain DaysDaily

Minimum

Daily

Maximum

Jan 16.6 27.7 270.4 18

Feb 16.9 25.9 256.9 17

Mar 16.3 25.4 183.1 17

Apr 15.2 24.8 50.5 9

May 12.9 22.9 20.1 6

Jun 10.8 20.9 7.2 6

Jul 10.3 20.2 11.1 8Aug 10.3 20.6 15.0 9

Sep 11.3 23.0 9.5 4

Oct 13.4 25.2 66.6 8

Nov 15.1 26.0 170.8 14

Dec 16.3 25.8 304.1 20

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