Characterization of Agriculturally Important

Rainfall variables for agricultural decision making,

Hawassa, Ethiopia Group members

Mr. Gizachew Legesse (EIAR/MARC) (l.gizachew@gmail.com)Mr. Minilik Tsega (EIAR/ HQ)Mr. Eshetu Zewidu (EIAR/MARC)Mr. Eskinder (EIAR/Mehoni ARC)

In Central Rift valley of Ethiopia, agriculture interfaces with extreme temporal and spatial variability of climate factors.

Amongst which rainfall is the most variable and the most important that greatly influence agricultural production and productivity.

For these reason, accurate analysis of rainfall is needed to generate valuable agro-climatic information that helps to reduce risks level of crop production.

Introduction

Study site

Rainfall analysis was performed for Hawassa zuria district that is found in Sothern Nation Nationality People (SNNP) regional state of Ethiopia.

1• Collecting and organizing

climate data and establishing flat databases suited for INSTAT and Genstat software

2• Turning climate data into

useful information through analysis and interpretation

3• Application of the

information for better decision making

Approach: Generation of Climate information through analysis

Rainfall variables and criteria for rainfall characterization1 • Start of the Season (SOS)

• Criteria: 3 days RT > 20mm and no dry spell of >10 days for the next 30 days

2

• End of the Season (EOS)• Criteria: any day after first of

September, when soil water starts to be at permanent deficit (WB < 50%).

3 • Length of Growing Period (LGP)• Criteria: EOS -SOS

4 • Total Season Water (TSW)• Criteria: The sum of rainfall total b/n SOS and EOS

5.

• Risk of a long dry spell

• The risk of longer dry spell of 5, 7, 10 and 15 days after sowing for any potential sowing date

Crop Coefficient for crop water requirement satisfaction index for maize crop variety having 140 day

maturity period • Value of crop coefficient for maize crop was taken from LEAP

software (fig) • Crop coefficient was interpolated for 14 dekade of the given

cropping season using INSTAT software• Computing CWRSI for maize variety having 140 day maturity

period

I. Summery of monthly rainfall total Hawassa, Ethiopia (1980-2010)

Jan_

t

Feb_

t

Mar_t

Apr_t

May_

t

Jun_

t

Jul_t

Aug_

t

Sep_

t

Oct_t

Nov_

t

Dec_

t

Rainf

all (m

m)

250

200

150

100

50

0

Monthly Rainfall total (1980-2010)

• Rainfall amount from April to September is greater than 100 mm per month.

I. Probability of occurrence of rainfall (1980-

2010)

p_rgfedcb

f_rgfedcb

f_oldgfedc

Overall chance of rain at Hawassa, Ethiopia (1980-2010)

Day of the year (DOY)400380360340320300280260240220200180160140120100806040200

Prob

abilit

ies

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

The overall chance of rainfall reveled that the probability of occurrence of rainfall in Hawassa ranges from 0.45 to 5.5 from 2nd dekade of April to the last dekade of September

fmgfedcb

Mean rain per rain day (mm) at Hawassa, Ethiopia (1980-2010)

Day of the month (DOY)400380360340320300280260240220200180160140120100806040200

Rain

fall (

mm

)

10

9.5

9

8.5

8

7.5

7

6.5

6

5.5

5

4.5

4

3.5

3

Average daily rainfall total per rainy day (1980-2010)

The average daily rainfall total per rainy days is 6.56 mm

Onset of rainy season(1980-2010)

SOSgfedcb

SOSWDgfedcb

Date of strat of the rain at Hawassa, Ethiopia (1980--2010)

Year2010200820062004200220001998199619941992199019881986198419821980

8 Jun

29 May

19 May

9 May

29 Apr

19 Apr

9 Apr

Based on the T-test result from the two onset definition (SOSWD) and (SOS ) , there is no significance difference in risk of failure (Replanting needed three times ).

The onset of rainy season in Hawassa ranges from April 1 to June 14.

Onset and Cessation of rainy season(1980-2010)

SOSgfedcb

EOSgfedcb

Year2010200520001995199019851980

Day

s of

Yea

r (D

OY

) 250

200

150

100

The mean onset and cessation of rainy season are 110th (April 2nd dekade) and 251th (September 1st dekade) DOY, respectively . Thus, the growing season accommodate about 141 days length of growing periods.

Probability of occurrence of LGP(1980-2010)

Percent Probability Plot of LGP

Length of growing period2001801601401201008060

Pe

rce

nt

100

90

80

70

60

50

40

30

20

10

0

From the result, the probability of occurrence of LGP, the chance of getting 140 days and less within the season is about 50%. one can recommend crop variety having 140 and less maturity period.

Risk of Dry spell, Hawassa, Ethiopia

sp5gfedcb

sp7gfedcb

sp10gfedcb

sp15gfedcb

Risk of dry spell based on the historic climatic condition (1980-2010)

Days of the Year (DOY)400350300250200150100500

Pro

ba

bili

ty

1

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

Analysis of the risk of dry spell longer than 5, 7, 10, and 15 days shows that the risk of dry spell of longer than 10 and 15 days is less than 1 % in the growing period (April 2nd dekade to September 1st dekade). While, 5 and 7 day risk of dry spell gradually increases in month of May about 2.5 and 6.2 %. The result informed that farmer can use 140 day crop variety while considering the adjustment of planting time not coincide the risk of dry spell in the month May with that of sensitive growth stage of the selected crop (like flowering time).

Summary of rainfall variables(SOS, EOS ,LGP and SRT)(1980-2010)

92

245

79

27.4

107

246

140

50.0

166

296

193

86.0

0

50

100

150

200

250

300

350

SOS EOS LGP Seasonal rainfall total (cm)

Day

s o

f y

ear

and

Sea

son

al r

ain

fall

to

tal

Rainfall variables

25%tile

Min/ Max

Median

75%tile

Crop Water Requirement Satisfaction Index for maize crop variety having 140 day

maturity period

Crop water requirement satisfaction index for 140 maize variety

CWSI

X86gfedcb

CWSI values for rainfed maize at Hawassa, Ethiopia (1980-2010)

Year2010200820062004200220001998199619941992199019881986198419821980

CWSI

100

95

90

85

80

75

70

65

60

CWRSI analytical result of 31 year cropping season reveals that Maize crop having 140 maturity period was fully satisfied in 11 years . whereas in less than 70 % is only 1 years (2000). This may cause yield reduction.

Rainfall characterization analytical result raveled that in Hawassa zuria districts have unimodal rainfall characteristics with average starting of main rainy season in 2nd dekade while ending in 1st dekade of September. The risk of dry spell longer than 7,10 and 15 days is relatively low (<3%) . Thus, season can accommodate 140 LGP having 500mm on average.

CWRSI result indicate that maize crop varieties having 140 day maturity period have been satisfied from seasonal rainfall. Based on the result , maize crop having 140 day maturity period can be successfully grown the Hawassa zuria districts

A knowledge of rainfall characteristics in terms of onset and cessation date , length of growing period, seasonal rainfall

amount and duration of intermittent dry spell as well as CWRSI , are very useful for planning various agricultural operations.

Conclusion

Thank you!Soil

Atmosphere

Plant/ Sugar cane Animal

S

P

/A

A

Soil

Atmosphere

Plant/ Sugar cane Animal

S

P

/A

A