Spatial Analysis of Changes and Detection of Jump of Monthly Evapotranspiration Time Series in Mazandaran

Reference evapotranspiration as an important indicator of demand for air evaporation is an important factor for climatic and hydrological studies. Due to the occurrence of climate change and the occurrence of large fluctuations in precipitation and the occurrence of mild to severe droughts, it is important to study the evapotranspiration changes. In this study, to investigate the temporal-spatial changes of trend and change point in the reference evapotranspiration time series for different seasons in Mazandaran province, 40 years data (1981-2020) from satellite networks (with a resolution of about 5 km) were used. Non-parametric Mann-Kendall, Sen's slope, Pettitt's test (Non-Parametric Rank Test) and quantile regression were used to investigate the changes in the trend and to present the range of fracture point changes in the evapotranspiration. The correlation coefficient between network evaporation-transpiration data and ground station data was estimated to be more than 0.9 in most of the stations and the average value of BIAS was 0.24. The results of Pettitt's test showed the time of sudden changes in reference evapotranspiration in spring, autumn and winter seasons in 2013, 2007-2010 and 1999, respectively, in most cases. Very high values of evapotranspiration increased in spring in the eastern half, in summer in the northern half and in winter in the southern and western strips (with a seasonal slope percentage of 45, 75 and 120 percent, respectively), but they decreased in autumn in the north of the province (with a slope of -45 percent). In general, significantly increasing slope rates for high values of evapotranspiration were higher than average. A significant increase in high amounts of evapotranspiration, especially in the dry season, will reduce water resources and disrupt the agricultural sector. Therefore, scientific and practical methods for managing reference evapotranspiration in the province should be considered.