خلاصة:
Drought is a repetitive phenomenon in different continents and its effects are not limited only to dry and semidry areas, but they could also be seen in areas with high rates of precipitation and in any season of year. One of the most important stages in monitoring the drought is to determine indices in order to analyze its intensity, continuity and frequency. The data related to the overall monthly precipitation collected from synoptic stations of the area during the statistical period of 1976-2005 which have been used for monitoring drought in Guilan and analyzing its characteristics. In the present study, continuity, intensity and frequency of drought have been extracted by using two indices, the standard distribution, and deciles and by the help of time series from standardized precipitation index. The results of this study indicated that the two analyzed methods give the same results and drought is not an infrequent phenomenon in the rainy part of northern Iran, but it is a repetitive and reversible phenomenon. The surveys indicated that in 1991 and 1995, an intense drought has happened in the province.
ملخص الجهاز:
Table 6- z values in 13 stations during a 30-year statistical period (Refer to page image) Based on the results obtained from Table 4 and the analysis of deciles 1 to 3, the years 1979, 1981, 1983, 1991, and 1995 have experienced very severe drought.
Table 5- Classification of the Standardized Precipitation Drought Index (Refer to page image) (Refer to page image) Figure 4- Drought distribution maps based on the decile index in the years 1979, 1991, and 1995 Continuation of Table 4- (Refer to page image) With the help of the above method and based on the results obtained from the analysis of deciles 1 to 3, the years 1979, 1981, 1983, 1991, and 1995 have been involved in very severe drought.
Table 3 shows deciles 1 to 3 of annual precipitation in Gilan province and Figure 1 shows the mapping of severe droughts during the aforementioned years.
(Refer to page image) Figure 2- Classification with the help of all meteorological elements using the Cluster method with the help of Minitab software (Refer to page image) Figure 1- Geographical location of the stations in Gilan province Table 1- Geographical location of the stations (Refer to page image) In the results obtained from the table, Rudbar and Manjil include a different climate from other parts of the province and have a severe climatic difference from other points in terms of obtained patterns such as average precipitation.
To monitor drought and analyze its characteristics in Gilan province, monthly precipitation data from the region's synoptic stations during the statistical period of 1976-2005 were used.
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