Analysis of precipitation and draughts on bih territory based upon standardized precipitation index (SPI)

Abstract

Most frequent indicator of the meteorological draught is the standardized precipitation index (SPI). This paper analyses SPI at 8 weather stations in Bosnia and Herzegovina. The calculations were perfomred per a calendar year and weather seasons between 1961 and 2010. The results indicate a trend of annual SPI12 to be relevant for only one weather station, but it was still positive refering to increased humidity. During the observed period, there was an increase in number of stations indicating extremely humid and extremely dry years but the changes were statistically irrelevant. The SPI3 trend for February (winter) was statistically immaterial at all stations but most observed locations showed increased draught. Not even SPI3 spring trend was statistically important nor did it have specific geografical regularities showing tendencies. In summer, there was an increased draugth at most locations and the negative value of SPI3 trend for August (summer) was statistically relevant at two weather stations (Bihać and Bileća). Over the last decade (2001-2010), at most locations there was a largest number of both dry and humid summers, which certainly shows more frequent extreme summer priods with reference to precipitation. At 7 of 8 stations, autumn was getting more humid but it was only in Bijeljina that SPI3 trend for November (autumn) was statistically significant. Most dry years were within 1981-1990 decade as NAO and AO indexes were the highest. On the other hand, 2001-2010 decade had most humid years and NAO index reached lowest values. In addition, the interannual precipitation variations were also largely affected by changes in atmospheric circulation. At season level, the best corelation with NAO and AO circulation parameters was in winter.

Najčešće korišćen pokazatelj meteorološke suše je Standardizovani indeks padavina (SPI). U ovom radu analiziran je SPI za 8 meteoroloških stanica u Bosni i Hercegovini. Proračuni su urađeni za kalendarsku godinu i meteorološke sezone, za period 1961-2010. Dobijeni rezultati ukazuju da je trend godišnjeg SPI12 značajan samo na jednoj stanici, ali je pozitivnog znaka, što znači da je došlo do povećanja vlažnosti. U posmatranom periodu prisutna je stopa rasta broja stanica na kojima su zabeležene ekstremno vlažne i ekstremno sušne godine, ali su i te promene statistički beznačajne. Trend SPI3 za februar (zimu) na svim stanicama je statistički beznačajan, ali je u većini posmatranih mesta došlo do povećanja sušnosti. Ni trend SPI3 za proleće ne pokazuje statističku značajnost ni na jednoj stanici, a nema ni određene geografske pravilnosti u znaku tendencije. Leti je došlo do povećanja sušnosti u većini mesta, a pri tome je negativna vrednost trenda SPI3 za avgust (leto) statistički značajna na 2 stanice (Bihać i Bileća). U poslednjoj dekadi (2001-2010) u većini mesta registrovaâ je najveći broj i sušnih i vlažnih leta, što nesumnjivo pokazuje povećanje učestalosti ekstremnih leta u pogledu padavina. Na 7 od 8 stanica jesen je sve vlažnija, ali je samo u Bijeljini pozitivan trend SPI3 za novembar (jesen) statistički signifikantan. Najveći broj sušnih godina registrovan je u dekadi 1981-1990., kada su NAO i AO indeks imali najviše vrednosti. S druge strane, dekada 2001-2010. izdvaja se sa najvećim brojem vlažnih godina, a u tom periodu je NAO indeks dostigav najniže vrednosti. I međugodišnje varijacije padavina su u velikoj meri pod uticajem promene atmosferske cirkulacije. Na sezonskom nivou, najbolja korelacija sa parametrima cirkulacije NAO i AO dobijena je za zimu