The potential impact of dust storms on precipitation in Khorasan Razavi Province

The rain process is affected by numerous environmental factors such as dust events and the interaction of these two events can influence the hydrological cycle. According to various reports on increasing of dust occurrences in different regions, this study aimed to investigate the potential impact of dust storms on rainfall in Khorasan Razavi during 2000-2013. The statistical method of "historical regression" was used to investigate dust effect on rainfall, which is based on comparison of observed rainfall with its prediction. Nine synoptic stations were selected as target stations. Regression equations were used to predict precipitation of target stations using the daily rainfall data of the hydrometric stations using the Least Squares Method. Then, the statistical ratio index for historical regression was calculated for each target station based on the observed and predicted rainfall values. The statistical ratio of each station was evaluated by Monte Carlo of permutation test using R-software. Since relative humidity variations play important role in the precipitation process, the correlation coefficient was calculated between the relative humidity and the statistical ratio index of each target station. The statistical test of correlation between relative humidity variables and the statistical ratio of historical regression were significant for all stations. The permutation tests for each station statistical ratio index showed a variable effect of dust on rainfall. The lowest statistical ratio index of 0.8 belonged to the Neyshabur Station with a relative humidity of 38%, whereas the highest statistical ratio index of 1.5 was found for Torbat Heydarieh Station with a relative humidity of 59.45%. In the present study, precipitation response to dust events was affected by relative humidity conditions. In a general conclusion, components of hydrological cycle does not have constant response to environmental variables and therefore, obtained comprehensive conclusions in atmospheric processes need more extensive studies.