Evaluation of evapotranspiration changes in the Aras basin using spatial high resolution MOD16 product

In this study, to evaluate the spatiotemporal changes of total evapotranspiration (ET) in the southern part of the Aras river basin, the MODIS Global Terrestrial Evapotranspiration ET Product (MOD16) for collection 6 for a statistical period of 20 years (2000-2019) was used. The spatial resolution of this data is 500 meters, and its temporal resolution is 8-day. First, the product ET data was compared with the evaporation stations data, and the accuracy of the product was evaluated and validated using correlation, determination coefficient, Root Mean Squared Error (RMSE), and Mean Absolute Error (MAE). Then ET time series was calculated for the whole basin and its trend was plotted. Annual ET maps and their spatial change maps for the 20-year period were also mapped. In addition, the area of each ET class was calculated as a percentage, and the class changes over time were examined. The results showed that during the period in general, the west of the basin had lower average evapotranspiration than the east All maximum cores except Parsabd core, have existed since 2000, but the maximum core in Parsabad has been formed since 2001 and has gradually. The results showed, the percentage of the spatial coverage of classes larger than 300 mm in 2010 and especially in 2019 has increased compared to the average period. It has almost doubled to the number of their respective classes in 2000. The ET of the basin and the type of land use and land cover were investigated to find a possible relationship between them. The most increasing change in the ET amount at irrigated agro-use in Parsabad, dense forests in Khodaafarin and Kaleybar, high quality pastures southeastern and agricultural-horticultural mixture in Ardabil and in constant, the most decreasing change in the ET amount at rainfed agricultural use, a mixture of poor pastures and other uses in the south of Parsabad, Bilesvar and Garmi Moghan and to some extent poor pastures in the west of the basin were observed. The increasing change in ET in the mentioned areas was partly due to their land use change. Annual land use changes in these areas showed that it was largely due to the change and reduction of grassland (pasture) and bareland to irrigated fields and the increase in the percentage of dense forest at Khodaafarin and Kaleybar, which led to an increase in ET. Regarding irrigated agricultural uses, it emphasizes the increasing water needs of plants and the need for further research and revision of the type of irrigation system and the use of indoor canals instead of open canals. The increase in ET can also be due to the increasing changes in the meteorological variables that affect it, such as air temperature, wind speed, etc. and how water resources management, the clarification of which requires detailed research. Increased water needs of plants will be only one of the consequences of increasing ET.