Abstract:Surface-based precipitation measurements with high accuracy on different spatial-temporal scales have a crucial importance in different land-use planning sectors, especially in arid and semi-arid regions, such as Iran. Because the density of spatial distribution of rain-gauges is not uniform throughout the country, satellite sensor technology is considered useful for precipitation monitoring over the study area. In this study, PERSIANN satellite-based rainfall data were validated through comparison with the APHRODITE surface-based precipitation data. The validation was carried out for annual and seasonal precipitation, as well as an inter-annual comparison. Our analysis was based on a visual comparison and a statistical approach, including linear regression and spatial correlation between APHRODITE and PERSIANN datasets for each 0.25°×0.25° grid cell in the entire country, in the Caspian Sea region, and in the Zagros Mountains, indicating spatial correlation coefficients of 0.62, 0.62, 0.47, respectively. Both APHRODITE data and PERSIANN data showed that spatial distribution of mean annual and seasonal precipitation over Iran has two main patterns: along the Caspian Sea and along the Zagros Mountain chain. In general, PERSIANN underestimates high rainfall rates by 5.5 mm/day in winter but overestimates the low rainfalls in annual and seasonal scales by 0.9 mm/day in summer.

Hail is a meteorological phenomenon that directly concerns to agricultural sector in Iran. Hailstorms affect crop yield that depends on the crop species and the phonological time. In this investigation, climatological study of hail fall has been performed through the available dataset in 118 synoptic stations across the country during a period of 20 years (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)) and hail event map was drawn. After analyzing the data and considering the produced maps, regarding the number of hail occurrence in the country, the following provinces respectively illustrate the highest annual mean of hail fall; Chaharmahal-e-bakhtiari, Ilam, Tehran and Kurdistan (about 4 times/yearly). In the next step, using the statistics of the agricultural insurance affairs during 1995-2005, cultivation areas damaged by hail fall in the farms of agricultural strategic products including; irrigated and rain fed wheat, grain, rice, cotton, sugar beet and potato have been studied, and then the classified maps of hail damage have been plotted for each province and crop. The produced maps indicate that most of the damaged area by hail fall has been related to irrigated wheat crop, with an annual average of 12690.8 hectares in the whole country, then the damaged crops were ordered respectively as following: rain fed wheat, sugar beet, potato, grain, cotton and rice.