1. Analysis of extreme precipitation in different time intervals using moving precipitation totals Tiina Tammets 1, Jaak Jaagus 2 1 Estonian Meteorological and Hydrological Institute 2 Department of Geography, University of Tartu

2. Outline Introduction, precipitation regime and extremes in Estonia Overview of the characteristics used for description of precipitation extremes Objectives of the study Using of moving precipitation totals as characteristics of precipitation regime Extreme precipitation in Estonia in dependence of a number of days and months in observed period Extreme precipitation in Estonia in case of very wet and dry conditions during 1957-2006 Trends in precipitation extremes in Estonia during 1957- 2006 Conclusions

3. Annual curve of monthly mean, maximum and minimum precipitation in 1966-2009, mean of the meteorological stations in Estonia

4. Precipitation in July and August 1966-2009, mean of the meteorological stations in Estonia

5. JUNE JULY AUGUST PRECIPITATION 2009 IN ESTONIA

6. Characteristics used for description of precipitation extremes quantiles of precipitation amounts; maximum number consecutive wet days (R>= 1 mm; 10 mm); maximum number of consecutive dry days with the threshold of 0.1 mm; 1 mm precipitation; number of heavy precipitation days in a month or year (R>=10 mm); number of very heavy precipitation days (R>=20 mm); number of dry and wet days in a month or in a year with chosen threshold; mean wet-day and dry-day persistencies; hydrothermical coefficient.

7. hydrothermical coefficient (HTK) : HTK =  Precipitation / 0,1*  Temperature

8. to show how much has been rained till this day not to show how much it rains in a day but For many purposes it is essential A day will be extreme day, if the amount of precipitation till this day has been too small or too large.

9. Objectives To define characteristics describing continuous dry and wet spells with various duration, which doesn’t divide time into months or 10-day periods To elaborate a method characterising climatology of extreme precipitation totals for any time periods (number of following days, months or years using moving totals) To detect the most severe wet and dry spells in Estonia during last 40-50 years and to analyse trends in days with precipitation extremes

10. Mathematically the sequence of moving totals (averages){s j (n),1  j  N-n+1} is derived from a sequence {a i, 1  i  N} obtained by taking the totals (averages) of the subsequent n terms: s j (n) = a j (by moving averages s j (n) = a j ),where N is the total number of days in the precipitation time series and n the number of days through which the moving average is calculated. We find drought and wet days by calculating s j (n) with time period n for each day i in the time series and choosing the days with values of s j (n), that are smaller or larger than the given threshold t. CALCULATING MOVING TOTALS (AVERAGES) To find the number of extreme days we have to calculate the moving total or average of precipitation time series

11. Counting of moving total n p n N days

12. Presentation of the extreme precipitation in any number of days, months or years

13. Extreme totals of precipitation for any number of days during 1966-2009 has been found in Tallinn, Vilsandi, Väike-Maarja, Võru Tartu and Pärnu stations Precipitation stations in Estonia

14. Dependence of maximum and minimum precipitation on the number of successive days at six stations in Estonia in 1966-2009

15. Dependence of maximum and minimum precipitation on the number of successive months at six stations in Estonia in 1966-2009

16. In agrometeorological studies of Estonia, the criterion of extremely wet conditions - mean daily precipitation 10 mm or more during successive 10 days is used. If the moving average for a 10-day period s j (10) >= 10 mm, then the last day of the period is regarded as a wet day. Extremely dry conditions for field plants mean that there is no precipitation during successive 20 days; then s j (20) = 0 and the last day of the period has been counted as a dry day. Extremely wet and dry days for Estonia

17. criteria: extremely wet conditions: when the mean daily amount of precipitation is 10 mm and more during 10 consecutive days extremely dry conditions: no precipitation during 20 consecutive days

18. Monthly relative number of wet days and days with precipitation ≥10 mm during 1957-2006, mean of the meteorological stations in Estonia

19. Monthly relative number of dry days and days without precipitation during 1957-2006, mean of the meteorological stations in Estonia

20. Maximum number of dry days in Estonia from May to August during 1957-2006

21. Number of wet and dry days (mean of 56 stations) and relative number of extreme (wet+dry) days in 1957-2006

22. The method of moving precipitation totals allows to 1.present maximum and minimum precipitation in different periods (from 1 day to 4-5 years) on graph, which gives complete information about precipitation extremes of a station. It allows also to compare extreme precipitation amounts in different stations for every time period. 2.connect precipitation extremes with the dynamics other characteristics of hydrological regime (for example soil moisture content, ground water level, river runoff etc.) and find the best predictants of precipitation regime for extreme situations of environment 3.extract the time intervals of extreme precipitation events to relate them to atmospheric circulation Conclusions

23. Using of the method of moving precipitation totals for the analysis of precipitation extremes in Estonia demonstrated that maximum and minimum precipitation in case of any number of successive days and months on the coast of open sea (Vilsandi) is significantly lower than in the continental Estonia occurrence of wet days is the highest in July and August while the number of dry days is maximal only in August and much lower in July maximum number of days without precipitation has been observed in May total number of extreme (wet and dry) days in Estonia has increased significantly during 1957-2006