Analysis of trends and change points in meteorological variables over the south of the Caspian Sea

This study analyzes linear trends and change points in meteorological variables including (a) sea surface temperature (SST) anomalies using three data sets: (1) level 4 of the optimum interpolated SST (OISST) of the Advanced Very High Resolution Radiometer (AVHRR), (2) the Objectively Analyzed Air-Sea Fluxes (OAFluxSST) project, and (3) the observed Improved Extended Reconstructed SST version 4 (ERSST); (b) evaporation (Evap); (c) air temperature at 2 m (AT2m); (d) wind speed at 10 m (wind10m); (e) specific humidity at 2 m (hum2m); and (f) precipitation used from Multi-Source Weighted-Ensemble Precipitation (MSWEP) over the south of the Caspian Sea (SCS) for the period 1982–2016. A significant upward trend is observed in annual SST anomalies over the SCS at the 5% level such that OISST, OAFluxSST, and ERSST data sets, respectively, indicating warming rates of about 1.2, 1.3, and 1.9 °C during the study period. Also, a significant upward trend is observed in annual Evap, AT2m, wind10, and hum2m at the 5% level. Both the Student t parametric and Mann-Whitney nonparametric Change Point Models (CPMs) suggested occurrence of common change point for annual OISST in 1994 over the SCS. For the same year, the applied Mann-Whitney test detected change point in annual OAFluxSST. The detected change point for OISST coincides with the change points of the annual hum2m and AT2m anomalies of synoptic stations (Bandar Anzali, Babolsar, and Ramsar), located at the southern coast of the Caspian Sea. The applied CPMs suggested significant change point in Evap in 1997, as evidenced by the increase of 60 mm in the mean annual value. The annual wind10m time series have a change point in 1995. The likelihood ratio test (LRT) confirms the CPM results. For example, the LRT indicates that the annual OISST and OAFluxSST anomalies over the periods 1983–1994 and 1995–2016 are drawn from normal distributions with different means such that difference in annual OISST and OAFluxSST anomalies means before and after 1994 are 0.89 and 0.83 °C, respectively.