Estimation of extreme wet and dry days through moving totals in precipitation time series and some possibilities for their consideration in agrometeorological studies

Moving totals of daily precipitation are a more exact tool for indicating the most extreme weather periods and their frequency than monthly or 10-day precipitation totals. Therefore the terms ʹextreme wetʹ and ʹextreme dryʹ are used for the last day of a period of calculating the moving total of precipitation if that is larger or smaller than the specified limits. These terms qualify a day with extra wet or dry meteorological and surrounding conditions. The number of extreme days and limits that lead to a large yield loss vary by crops and phenological phases. Calculation of moving totals in precipitation long time series in any number of successive days allows presenting the dependence of the observed maximal and minimal amount of precipitation on the number of successive days in a period. Such dependence seems to be useful in estimating the climate resources in an area. Examples are given for Jogeva, Parnu and Ristna precipitation time series of 1957-2008. Estimation of extreme wet and dry weather conditions on the basis of moving totals of daily precipitation allowed distinguishing the most drastic periods and trends of the precipitation regime in Estonia in the last 50 years. A day is considered as extreme wet when the moving total of precipitation is at least 10 mm on 10 successive days leading up to this day. A day is considered as extreme dry when there was no precipitation during the successive 20 days till the observed day. By these criteria years with especially wet or dry periods are easily distinguished. Inter-annual variability of the average number of wet and dry days in Estonia increased notably in 1957-2006. The growing trend of annual total number of extreme (wet + dry) days is statistically significant.