Drought Monitoring in Cambodia

CHHINH Nyda chhinh.nyda@rupp.edu.kh

We Can Monitor DROUHGT? Tannehill (1947) notes:

“We may truthfully say that we scarcely know a drought when we see one. We

welcome the first clear day after a rainy spell. Rainless days continue for some time and we are pleased to have a long spell of fine

weather. It keeps on and we are a little worried. A few days more and we are

really in trouble. The first rainless day in a spell of fine weather contributes as much to the drought as the last, but no one knows how serious it will be until the last dry day is

gone and the rains have come again … we are not sure about it until the crops have withered and died”.

Drought Damage in Cambodia

0

5

10

15

20

25

30

35

40

45

0

4

8

12

16

20

24

Ko

h K

ong

Pai

llin

Odd

or

Me

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Kra

tie

Kep

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ukv

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Phn

om

Pen

h

Kam

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Ch

am

Mo

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Rat

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Pre

ah V

ihea

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Kam

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Rea

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Kam

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Tho

m

Pur

sat

Ban

teay

Mea

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ey

Kam

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Ch

hn

ang

Kan

dal

Svay

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Pre

y V

eng

Bat

tam

ban

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Take

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Kam

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Speu

Very Low Low Medium High Very High

Are

a d

amag

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y d

rou

ght

for

20

04-

20

05

in

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ha

Freq

uen

cy o

f d

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for

1988

-20

11

Frequency Damage in 2004-05

Drought and Rice Calendar

How Drought Is Monitored?

Drought Indices Description

Percent of Normal

Actual precipitation / normal precipitation ( a 30-year-mean)

Standardized Precipitation Index

Probability of precipitation for any time scale

Palmer Drought Severity Index

Soil moisture algorithm for relative homogeneous regions

Crop Moisture Index A Palmer derivative to reflects moisture supply in the short term

Deciles Groups monthly precipitation occurrences into Deciles

Major drought indices

Why Standardize Precipitation Index

Standardize Precipitation Index (SPI): • Need only rainfall data • Can be used for early warning of drought onset • Assess drought severity • Assess different time scales

Used by:

• The U.S (National Drought Mitigation Centre) • Asia (such as India) • Europe (European Drought Centre)

SPI and Drought in Kampong Speu Province

SPI and Drought in Kampong Speu Province

-3

-2

-1

0

1

2

3

1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009 2011

June August November

SPI one month period

SPI and Drought in Kampong Speu Province

SPI three month period for November

-2

-1

0

1

2

3

4

1983 1986 1989 1992 1995 1998 2001 2004 2007 2010

1988 1990 1994 2004 2006

SPI and drought in Kampong Speu Province

-

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

1994 1996 1998 2000 2002 2004 2006 2008 2010

(Are

a d

estr

oye

d in

ha)

(Year)

Paddy rice and Cash crop field damages (in ha) by drought in KPS, 1994-2010

Software to Run SPI

• SPI runs in C language at http://drought.unl.edu/MonitoringTools/DownloadableSPIProgram.aspx

• SPI runs in R language at http://cran.r-project.org/web/packages/SCI/

• World Meteorology Organization development manual for SPI

run in C language at http://www.wamis.org/agm/pubs/SPI/WMO_1090_EN.pdf

• Meteorological Statistics can be found from: Thom, Herbert Conrad Schlueter. (1966). Some methods of climatological analysis: Secretariat of the World Meteorological Organization.

SPI formula, if use EXCEL

Gamma function found to fit with meteorological data

𝑔 𝑥 =1

𝛽𝛼𝛤(𝛼)𝑥𝛼−1𝑒

−𝑥𝛽

Where β is a scale parameter, α is a shape parameter, and Γ(α) is the ordinary gamma function of α.

𝛼 =1

4𝐴(1 + 1 +

4𝐴

3)

And 𝛽 =𝑥

𝛼 where 𝐴 = 𝑙𝑛𝑥 −

𝑙𝑛𝑥

𝑛

Let Monitor Drought

With proper data recording, drought can be monitored and possibly avoided by using Standardized Precipitation Index.

Thank You!