Temporal and spatial distribution of extreme precipitation indices over the lake Urmia Basin, Iran

Climate extremes have more direct and significant impact than average state on social andecological systems. In this study temporal and spatial distribution of extreme precipitationevents were analyzed based on the daily precipitation data of seven meteorological stationsin the Lake Urmia Basin in Iran from 1987 to 2014. Eleven indices of precipitationextremes were selected and calculated using the RClimDex software. The Mann-Kendalltest was employed to assess trend in extreme precipitation indices, and the Sen s Estimatortest was used to determine the slope of the significant trends. Results demonstrate thatconsecutive dry days (CDD) exhibit an increasing trend. The other indices of precipitationextremes, Consecutive wet days (CWD), heavy precipitation days (R10mm), heavierprecipitation days (R20mm), heaviest precipitation days (R25mm), maximum 1-dayprecipitation (RX1day), maximum 5-day precipitation (RX5day), very wet dayprecipitation (R95), extremely wet day precipitation (R99), simple daily intensity index(SDII), and wet-day precipitation (PRCPTOT) show decreasing trend and time of change inmost indices starting from 1995-1996. However, all the linear trends for each index are notstatistically significant. Decreasing trends in precipitation days were greater than those inprecipitation indices. The slope of trends in extreme precipitation indices showed that thehighest slope of the decreasing trend occurred in wet-day precipitation, consecutive drydays and very wet day precipitation. Spatial distribution for precipitation extremesexhibited a declining trend in most regions in the Lake Urmia Basin. Furthermore, theextreme precipitation indexes had positive correlations with the annual total precipitation,and their correlation coefficients were statistically significant at the 1% significance level,except for consecutive dry days.

کلیدواژه ها:

Precipitation extremes ، Spatial and temporal distribution ، Mann-Kendall test ، Sen s Estimator test ، Lake Urmia Basin.1