Rainfall and climate variables used in the literature for the definition of rainfall thresholds for the initiation of landslides. Table lists the variable, the units of measure most commonly used for the parameter, and the author(s) who first introduced the parameter. Nomenclature is not consistent in the literature, and different definitions have been used for the same or similar variables.

VARIABLE	DESCRIPTION	UNITS	FIRST INTRODUCED
D	Rainfall duration. The duration of the rainfall event or rainfall period.	h, or days	Caine (1980)
DC	Duration of the critical rainfall event.	h	Aleotti (2004)
E(h),(d)	Cumulative event rainfall. The total rainfall measured from the beginning of the rainfall event to the time of failure. Also known as storm rainfall. “h” indicates the considered period in hours; “d” indicates the considered period in days.	mm	Innes (1983)
EMAP	Normalized cumulative event rainfall. Cumulative event rainfall divided by MAP (EMAP=E/MAP). Also known as normalized storm rainfall.	-	Guidicini and Iwasa (1977)
C	Critical rainfall. The total amount of rainfall from the time of a distinct increase in rainfall intensity (t0) to the time of the triggering of the first landslide (tf).	mm	Govi and Sorzana (1980)
CMAP	Normalized critical rainfall. Critical rainfall divided by MAP (CMAP=C/MAP).	-	Govi and Sorzana (1980)
R	Daily rainfall. The total amount of rainfall for the day of the landslide event.	mm	Crozier and Eyles (1980)
RMAP	Normalized daily rainfall. Daily rainfall divided by MAP (RMAP=R/MAP).	mm	Terlien (1998)
I	Rainfall intensity. The amount of precipitation in a period, i.e., the rate of precipitation over the considered period. Depending on the duration of the measuring period, rainfall intensity measures peak or average precipitation rates.	mm/h	Caine (1980)
IMAP	Normalized rainfall intensity. Rainfall intensity divided by MAP (IMAP=I/MAP).	1/h	Cannon (1988)
IMAX	Maximum hourly rainfall intensity. The maximum hourly rainfall intensity.	mm/h	Onodera et al. (1974)
IP	Peak rainfall intensity. The highest rainfall intensity (rainfall rate) during a rainfall event. Available from detailed rainfall records.	mm/h	Wilson et al. (1992)
Î(h)	Mean rainfall intensity for final storm period. “h” indicates the considered period, in hours, most commonly from 3 to 24 hours.	mm/h	Govi and Sorzana (1980)
IC	Critical hourly rainfall intensity.	mm/h	Heyerdahl et al. (2003)
If	Rainfall intensity at the time of the slope failure. Available from detailed rainfall records.	mm/h	Aleotti (2004)
IfMAP	Normalized rainfall intensity at the time of the slope failure. Rainfall intensity at the time of the slope failure divided by MAP (IfMAP=If/MAP).	1/h	Aleotti (2004)
A(d)	Antecedent rainfall. The total (cumulative) precipitation measured before the landslide triggering rainfall event. “d” indicates the considered period in days.	mm	Govi and Sorzana (1980)
AMAP	Normalized antecedent rainfall. Antecedent rainfall divided by MAP (AMAP=A/MAP).	-	Aleotti (2004)
A(y)	Antecedent yearly precipitation up to date of the event. The total (cumulative) yearly precipitation measured before the landslide triggering rainfall event.	mm	Guidicini and Iwasa (1977)
A(y)MAP	Normalized antecedent yearly precipitation up to date of the event. Antecedent yearly precipitation divided by MAP (A(y)MAP=A(y)/MAP).	-	Guidicini and Iwasa (1977)
FC	Sum of normalized antecedent yearly precipitation and normalized event rainfall (FC=A(y)MAP+EMAP). Also known as “final coefficient”.	-	Guidicini and Iwasa (1977)
MAP	Mean annual precipitation. For a rain gauge, the long term yearly average precipitation, obtained from historical rainfall records. A proxy for local climatic conditions.	mm	Guidicini and Iwasa (1977)
RDs	Average number of rainy-days in a year. For a rain gauge, the long term yearly average of rainy (or wet) days, obtained from historical rainfall records. A proxy for local climatic conditions.	#	Wilson and Jayko (1997)
RDN	Rainy-day normal. For a rain gauge, the ratio between the MAP and the average number of rainy-days in a year (RDN=MAP/RDs).	mm/#	Wilson and Jayko (1997)
N	Ratio between the MAP of two different (distant) areas.	-	Barbero at al. (2004)