International workshop on climate and land degradation frequency of wet and dry spells in tanzania
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International Workshop on Climate and Land Degradation Frequency of Wet and Dry Spells in Tanzania. F. F. Tilya and M. S. Mhita Tanzania Meteorological Agency Email: met@meteo.go.tz, Website: www.meteo.go.tz. T A N Z A N I A. Tanzania. Physical features. Objective.

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InternationalWorkshop on Climateand Land DegradationFrequency of Wet and Dry Spells in Tanzania

F. F. Tilya and M. S. Mhita

Tanzania Meteorological Agency

Email: met@meteo.go.tz,

Website: www.meteo.go.tz


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T

A

N

Z

A

N

I

A


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Tanzania

Physical features


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Objective

To review and assess the extent to which weather and climate data and information can be used in Tanzania to monitor and assess land degradation


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Data

41 years

(1960 – 2000)

of daily

rainfall

records

obtained

from

Tanzania

Meteorological

Agency.


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Method

  • Wet (dry) day is defined as any day recording at least (at most) one millimeter of rainfall;

  • Moreover a wet (dry) spell was put to occur when sequence of wet (dry) days are preceded and followed by dry (wet) days;

  • Frequencies of wet (dry) spells run were then derived from the daily data from a location during the period of data


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Method ctd…

  • If a spell of ith days occurs in a month jand year kthen the number of occurrences of the spell during a month and year for a station was expressed mathematically as

    where n and m are spell runs and total number of years respectively.


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Method ctd…

  • A routine scans across each season for the longest spell

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

1960 d d d d d d d d d d d d

1961 d d d d d d d d d d d d

1962 d d d d d d d d d d d d

.

.

.

2000 d d d d d d d d d d d d


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Results:

Temporal distribution of wet spell lengths

Engare Rongai (slopes of mount Kilimanjaro)


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Results:

Temporal distribution of dry spell lengths

frequency of dry spells run during the October - May at Mahenge


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Spatial distribution of maximum runs of wet spellsat some stations


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Spatial distribution of maximum runs of dry spellsat some stations


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Summary

  • Wet spells of durations of over 10-days prevailed during peak rainfall months and dominant over high lands and close to large water bodies including Lakes Victoria and Tanganyika and along the coast.

  • Comparatively, this study indicates that several stations are recording fewer wet spells. Ogallo and Chillambo, 1984 using daily rainfall for 1950-1980 observed a record wet spell of 47 days while this study had a maximum run of 28 days!


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Summary cont…

  • Similarly, the maximum number of dry spells are noted to escalate.

  • Alusa and Gwage, 1978 analyzed maximum runs of 61 dry spells in central Tanzania. This study observed a record of 249 dry spells in the same area.


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Conclusion remarks

  • These results may constitute some useful information to monitor and assess land degradation in Tanzania

  • Developing appropriate strategies for reducing land degradation and restoring degraded land threatened by refugees, population growth, human activities and climatic variations and change.


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Ahsante sanaThank you