عنوان مقاله [English]
The spatiotemporal changes of precipitation may be result in some dangerous phenomena like as runoff and drought. During recent years to accompany with hot climate change dialogs trend of changes in many climate parameters specially precipitation has been subject of almost researches in Iran and out of it.
With quick look at researches over precipitation, we can observe that subject of almost is variation in amount precipitation and its impact on the river outflow, the frequency of rainy days (0.1, 0.5 and 1 mm), the frequency of extreme precipitation (quintiles, 90, 95 and 99 percentiles), amount of precipitation result from that rainfalls and detection and trend of drought occurrence by different indices (specially precipitation). The precipitation has vary non known behaviors and although many worthwhile studies have been done by researches but so far not any one studied precipitation persistency over Kurdistan Province.
To doing this study daily precipitation data from 188 synoptic, climatic and rain gauge stations in province and out of it during 1/1/1340 to 29/12/1388 extracted from power and meteorology organizations. By statistic spatial Kriging method for every days one map created. Then data over province on the 811 pixels that covers whole of province extracted. One data base in 17897*811 dimensions has been created that locate on the rows days and on the columns pixels. For every pixels precipitation persistency calculated. The methods of applied in this study obtained from Nazari Pour et al., 1390. The rainy days consider a days that amount of precipitation equal and more than 0.5 mm during 24 hours. The extensive of every precipitation persistency over Kurdistan province (AP_i) by following formula has been calculated (Nazari Pour et al., 1390):
(1) AP_i=(â_(j=1)^nâP_i )/NÃ100
That i equal to persistency that changes from 1 to 37 days and j is pixels that persistency occurred on it that vary from 1 to 811. P is the precipitation persistency and N is the total of pixels. The contribution of the precipitation persistency in rainy days and amount precipitation over every pixels calculated by 2 and 3 formula:
(2) X(j,i)=R_(j,i)/(â_(i=1)^37âR_(j,i) )Ã100
That X(j,i) is the contribution of rainy days on the j that with persistency of i and R_(j,i) is the rainy days frequency on the j that obtained from of i^th persistency.
(3) Y(j,i)=P_(j,i)/(â_(i=1)^37âP_(j,i) )Ã100
In the above formula P(j,i) is the amount of precipitation on the j that obtained from of i^th persistency and Y_(j,i) is the percent of precipitation contribution on the j from of i^th persistency. The trend of persistency precipitation over each pixels during study period evaluated by Mann Kendal non parametric test in 95% confidence level.
The results show that persistency precipitation of 1 to 9 days recorded on the whole province. The highest extensive significant changes in contribution of persistency precipitation in rainy days and amount relevant to January and April. Also the highest changes among persistency precipitations observed for 1 days persistency precipitations. The long time persistency precipitation didnât have any changes during study period. The contribution of short time persistency precipitations in rainy days and amount over semi eastern parts of province show decreasing trend. In contrast for semi western parts short time persistency precipitations have increasing trend. The decrease in precipitation over semi eastern parts and concentration and ascendency of precipitation intensity in semi western parts of province results in many problems for water management.