CR 74:231-250 (2018)  -  DOI: https://doi.org/10.3354/cr01503

ABSTRACT: The evaluation of precipitation extremes and the usage of appropriate drought indices are very important for assessment of natural disasters (i.e. floods and drought). For this purpose, we calculated values of indices that reflect precipitation extremes and 3 drought indices, i.e. the composite index (CI), standardized precipitation evapotranspiration index (SPEI), and reconnaissance drought index (RDI), with reformulation of pan evaporation and Penman-Monteith equations (denoted as CI-Pan, RDI-Pan, RDI-PM, and SPEI-PM), based on observed data fom 1961-2005. Output from Coupled Model Intercomparison Project Phase 5 (CMIP5) historical model simulations was also used to identify discrepancies in the model simulations. The results showed that wet-day precipitation increased at a rate of 1.9 mm yr^-1 over the entire study area. During the whole time period, the simple daily intensity index exhibited a non-significant decreasing trend compared to other precipitation indices. The number of consecutive wet days showed a negative trend, while the number of consecutive dry days showed a positive trend with a slope of 0.33 d yr^-1. Very small differences were found between the results of the multi-model ensemble mean and the values of the extreme precipitation indices assessed from the in situ stations. The performance of reformulated drought indices is significant in monitoring drought events in the study area. A comparison of the indices showed that the performance of reformulated drought indices is better than that of the standard RDI and SPEI at all stations. The highest CI-Pan value (0.23) was observed in July, and the 2 lowest values, -0.6 and -0.7, were observed in April and September, respectively, indicating that the latter 2 months are highly prone to drought.

KEY WORDS: Drought · Precipitation · General circulation model · Water resources management · Pan Evaporation