International Workshop on Climate and Land Degradation Frequency of Wet and Dry Spells in Tanzania

1. 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

2. T A N Z A N I A

3. Tanzania Physical features

4. 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

5. Data 41 years (1960 – 2000) of daily rainfall records obtained from Tanzania Meteorological Agency.

6. 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

7. 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.

8. 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

9. Results: Temporal distribution of wet spell lengths Engare Rongai (slopes of mount Kilimanjaro)

10. Results: Temporal distribution of dry spell lengths frequency of dry spells run during the October - May at Mahenge

11. Spatial distribution of maximum runs of wet spellsat some stations

12. Spatial distribution of maximum runs of dry spellsat some stations

13. 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!

14. 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.

15. 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.

16. Ahsante sanaThank you