Comparison of different drought indices

Uslijed nedostatka oborina u vremenskom razdoblju dovoljno dugog trajanja može doći do nastanka suše. Nemoguće ju je potpuno spriječiti, ali redovitim praćenjem i ranim upozorenjima moguće je smanjiti njezine posljedice. U ovom diplomskom radu različitim metodama je proveden proračun analize suše na mjesečnoj i sezonskoj razini. Suša je analizirana za područje Donjeg Miholjca u razdoblju od 1981. do 2018. godine. Proveden je proračun analize suše pomoću osam različitih metoda. Metoda decila (DI) zasniva se na rangiranju oborina od najmanje prema najvećoj nakon čega se niz dijeli u desetine distribucije. Prvih 10 % vrijednosti ukazuju na najsušnije uvjete, a zadnji decil na uvjete vlažnije od prosječnih. Indeks aridnosti (AI) fleksibilna je metoda koja predstavlja omjer sume mjesečnih oborina i potencijalne evapotranspiracije. Najčešće primjenjivan je standardizirani indeks oborine (SPI), a određuje se na temelju mjesečnih podataka o oborini. Indeks anomalije oborina (RAI) također uzima u obzir samo podatke o mjesečnim oborinama tijekom analize suše. U novije vrijeme pojavila se modifikacija indeksa SPI, standardizirani indeks oborina i evapotranspiracije (SPEI) koji osim podataka o oborinama u obzir uzima i evapotranspiraciju. Za proračun standardiziranog indeksa protoka (SSI) dnevni protoci rijeke Drave dobiveni su s mjerne postaje Belišće, a za proračun standardiziranog indeksa razine podzemnih voda (SWI ili SGI) podaci su dobiveni s pijezometra P-58 (4120) nedaleko od Donjeg Miholjca. Rezultati svih metoda rangirani su u sedam razreda vlažnosti ili sušnosti, a rezultati indeksa aridnosti podijeljeni su u pet razreda. Provedena je usporedba svih metoda na osnovu rezultata o stanju sušnosti na sezonskoj razini.Due to the lack of precipitation for a sufficiently long period of time, a drought can occur. It is impossible to completely prevent it, but regular monitoring and early warnings can reduce its consequences. In this master thesis, the calculation of the drought analysis at the monthly and seasonal level was carried out using different methods. The drought was analyzed for the area of Donji Miholjac in the period from 1981 to 2018. The calculation of drought analysis was carried out using eight different methods. The decile method (DI) is based on the ranking of precipitation from minimum to maximum, after which the series is divided into tens of distributions. The first 10 % of values indicate the driest conditions, and the last decile indicates wetter than average conditions. The Aridity Index (AI) is a flexible method that represents the ratio of the sum of monthly precipitation and potential evapotranspiration. The Standardized Precipitation Index (SPI) is most commonly used, and is determined on the basis of monthly precipitation data. The Rainfall Anomaly Index (RAI) also takes into account only monthly precipitation data during the drought analysis. Recently, there has been a modification of the SPI, a Standardised Precipitation and Evapotranspiration Index (SPEI) which takes into account evapotranspiration in addition to precipitation data. For the calculation of the Standardized Streamflow Index (SSI), the daily flows of the river Drava were obtained from the measuring station Belišće, and for the calculation of the Standardized Water-level Indeks (SWI or SGI), the data were obtained from the piezometer P-58 (4120) not far from Donji Miholjac. The results of all methods are ranked in seven grades of humidity or dryness, and the results of the Aridity Index are divided into five classes. A comparison of all methods was made based on results on the drying situation at seasonal level