Spatial and Temporal Displacements in Wet and Dry Periods in the Southeast of the Caspian Sea: Golestan Province in Iran

The global warming phenomenon has had a great impact not only on the temperature patterns of the regions, but also on the spatial-temporal patterns of the occurrence of wet and dry days. As some areas have increased (decreased) the number of dry days, the result of these changes requires new approaches to water management in these areas. Golestan province in northern Iran is one of the provinces in south of Caspian Sea, where evidence suggests a decrease in precipitation days as well as the temporal displacement of precipitation days from the cold period to the warm period of the year. Therefore, the present study investigates the probability of occurrence of wet and dry days based on the one-time Markov chain method, as a change of decade. Thus, in this research, precipitation data from 197 precipitation stations for a period of 40 years from 1971 to 2010 was used. In this study, based on the most internal consistency of different regions in terms of the occurrence of wet and dry days, eight different spatial zones were identified. The results of this study indicate that the continuity of the wetter periods in the eight-cluster zones of Golestan province indication that the length of the wetter period has decreased in most months. The highest decrease in July was on average 0.20 days per decade. However, in August, September, and October, it reached its lowest level. In August and September, clustered zones in the eastern regions of the province show an increase in the longer period. This indicates that during the last decades throughout the second half of the summer, rainfall has increased in the province.