Evaluating Satellite-Derived Evapotranspiration Trends: A Case Study of the Marksovsky District of the Saratov Region (RF)

At the southeastern European part of Russia (SEER), large areas of drylands with rainfed agriculture are affected by the depletion of soil water resources (SWR) in root zones. This depletion of SWR caused by climate change and extreme weather events (heat waves, droughts, water shortages) threatens food security. Climate observation analyses of this territory show that there are progressive and substantial drying land surfaces due to the increasing air temperature and diminishing precipitations. Actual evapotranspiration (ET_a) is one of the major indicators of the agro-hydrological changes in dryland areas. In this paper, trends of ET _a ^w of warm time periods (2003-2017) were calculated using remote sensing data for the territory of the Marksovsky District of the Saratov Region, situated at the left bank, down part of the Volga River. For this purpose, we used multiyear datasets, derived from the MOD16 product, inside the administrative border of the study site (2003–2017). These datasets were used to develop time series of aggregated evapotranspiration ET _a ^w rates for all pixels within the study site. The result of the time series trend computed by the Mann–Kendall test code indicates that ET _a ^w for the rainfed part of this study site decreased during 2003–2010 and increased during 2010–2017. For a territory with artificial crop irrigation, positive and negative trends were noted during 2003–2010, as well as positive trends during 2010–2017. Spatial distribution analyses of obtained trends of ET_a over the study region showed that it was affected by precipitations as well as by air humidity and temperature fluctuations.