Precipitation and temperature of the southwest Caspian Sea region during the last 55 years: their trends and teleconnections with large-scale atmospheric phenomena

摘要

Climate data from the southwest coast of the Caspian Sea (CS) were statistically analysed to find connections with large-scale atmospheric variabilities and regional impacts. The study area is characterized by a subtropical humid climate. This enclave of high precipitation is extremely important for Iranian food production and is recognized for its high biodiversity. The data sets were investigated for inconsistencies before carrying out the main investigations, and several problems have been identified. The results show three distinct climatic periods in the temperature time series since 1956: 1956 to 1975 with values near to the overall mean, 1977 to 1995 with values lower by 0.5 degrees C and from 1996 to 2010 with values higher by 0.5 degrees C. These periods can be positively correlated with rapid sea level changes of the CS. Moreover, an agreement exists between the three climatic periods and the North Atlantic Oscillation (NAO) variability. The sea surface temperature of the southern CS is shown to be the driving force of the 2m temperatures in the study area. While temperature changes are in accordance with NAO variability, the precipitation variations show connections with ENSO and less with NAO. The trends of precipitation during the period are diverse but display mostly a weak decrease, while the trends of temperature display a clear increase, larger than that for global mean temperatures, overlaid with inter-decadal variations.