Satellite-based soil moisture retrieval (SSMR) is crucial for various applications such as crop yield estimation, land surface-climate interactions, drought monitoring, irrigation management, and urban water management. SSMR covers two key areas: surface soil moisture (SSM) analysis, which focuses on the top 3–5 cm of soil, and root-zone soil moisture (RZSM) estimation, which extends to depths of 30–110 cm. While remote sensing has been widely utilized for large-scale SSM estimation, its application for farm-scale RZSM retrieval and soil hydraulic parameter estimation remains underexplored and previous studies have primarily assimilated either land surface temperature (LST) or SSM separately. This research, thus, emphasizes the interdependency between soil moisture and temperature and proposes a new method using a reduced-order variational approach to simultaneously assimilate LST and SSM data from thermal and microwave satellite remote sensing into the HYDRUS-1D model. Our framework aims to estimate soil hydraulic parameters and RZSM profiles at the farm scale (~30m-1km) using data from MODIS, LANDSAT-8, and SMAP, by combining the horizontal coverage and spatial resolution of remote sensing with the vertical coverage and temporal continuity of the soil moisture simulation models. We have designed an Observing System Simulation Experiment (OSSE) to evaluate this framework. Preliminary results indicate that coupling soil temperature and moisture models enhances the accuracy of surface energy and water flux predictions. Additionally, it enables more precise estimation of soil hydraulic parameters compared to models that assimilate only LST or SSM data. These findings highlight the potential of using freely available satellite data to estimate RZSM profiles and soil hydraulic parameters globally, thereby reducing the reliance on costly ground-based measurements. This research advances hydrological modeling capabilities and demonstrates how integrated satellite observations can improve water resource management, particularly in underserved communities.

Since the dawn of civilization water reservoirs have been used to support irrigation and livestock in many arid regions of the world [1]. Evaporative losses diminish reservoir storage efficiency; hence, different means such as floating covers have been proposed to reduce losses. While laboratory and field studies have evaluated effects of cover properties (e.g., geometry, thermal, and radiative characteristics) on Evaporation Suppression Efficiency (ESE) [2-4], the influence of seasonal climate variability on ESE remains understudied. We conducted long-term field measurements in two identical water reservoirs (area: 25 m2, depth: 2 m) in a dry region to investigate how seasonal variations in atmospheric conditions affect ESE. We compared the evaporation rate and water temperature profile in a reservoir covered with Styrofoam discs (D: 50 cm, H: 5 cm) with those in an uncovered reservoir. For 90% surface coverage, measurements indicate that ESE varied from nearly 80% in summer to about 60% in winter. Temperature variations and radiative energy storage within the reservoirs show that the opaque and thermal insulating characteristics of the Styrofoam discs and their effects on wind-induced mixing lead to thermal stratification and formation of a seasonal thermocline in the covered reservoir. These affect the exchange of accumulated summer heat with overlying air resulting in a slower reduction in evaporation rate compared to the uncovered reservoir in cold seasons. The study sheds new light on thermal regimes and ESE in partially covered multiuse reservoirs under different climatic conditions. References [1] M. Aminzadeh, N. Friedrich, S. Narayanaswamy, K. Madani, and N. Shokri, Evaporation Loss from Small Agricultural Reservoirs in a Warming Climate: An Overlooked Component of Water Accounting, Earth’s Future, 12(1), 2024. [2] M. Aminzadeh, P. Lehmann, and D. Or, Evaporation suppression and energy balance of water reservoirs covered with self-assembling floating elements, Hydrology and Earth System Sciences, 22(7), 2018. [3] M. Bakhtiar, M. Aminzadeh, M. Taheriyoun, D. Or, and E. Mashayekh, Effects of floating covers used for evaporation suppression on reservoir physical, chemical and biological water quality parameters, Ecohydrology, 15(8), 2022. [4] P. Lehmann, M. Aminzadeh, and D. Or, Evaporation Suppression from Water Bodies Using Floating Covers: Laboratory Studies of Cover Type, Wind, and Radiation Effects, Water Resources Research, 55(6), 2019.