Browsing by Author "Moran, M. S."

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    Assimilating remote sensing observations of leaf area index and soil moisture for wheat yield estimates: An observing system simulation experiment
    (American Geophysical Union, 2012-05-17) Nearing, G. S.; Crow, W. T.; Thorp, K. R.; Moran, M. S.; Reichle, R. H.; Gupta, H. V.; University of Arizona; United States Department of Agriculture (USDA); National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University of Alabama Tuscaloosa
    Observing system simulation experiments were used to investigate ensemble Bayesian state-updating data assimilation of observations of leaf area index (LAI) and soil moisture (theta) for the purpose of improving single-season wheat yield estimates with the Decision Support System for Agrotechnology Transfer (DSSAT) CropSim-Ceres model. Assimilation was conducted in an energy-limited environment and a water-limited environment. Modeling uncertainty was prescribed to weather inputs, soil parameters and initial conditions, and cultivar parameters and through perturbations to model state transition equations. The ensemble Kalman filter and the sequential importance resampling filter were tested for the ability to attenuate effects of these types of uncertainty on yield estimates. LAI and theta observations were synthesized according to characteristics of existing remote sensing data, and effects of observation error were tested. Results indicate that the potential for assimilation to improve end-of-season yield estimates is low. Limitations are due to a lack of root zone soil moisture information, error in LAI observations, and a lack of correlation between leaf and grain growth.
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    Hydrologic response to precipitation pulses under and between shrubs in the Chihuahuan Desert, Arizona
    (American Geophysical Union, 2010-10-08) Moran, M. S.; Hamerlynck, E. P.; Scott, R. L.; Stone, J. J.; Collins, C. D. Holifield; Keefer, T. O.; Bryant, R.; DeYoung, L.; Nearing, G. S.; Sugg, Z.; Hymer, D. C.; United States Department of Agriculture (USDA); University of Arizona; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University of Alabama Tuscaloosa
    Observations of the temporal and spatial distribution of poststorm soil moisture in open shrublands and savannas are limited, yet they are critical to understanding the interaction and feedback between moisture distribution and canopies. The objective of this analysis was to study the hydrologic impacts of precipitation pulses on the upper layer of soils under and between shrubs. The study was based on measurements of precipitation, runoff, and under-and between-shrub soil moisture over a period of 20 years (1990-2009) at a shrub-dominated site in the Walnut Gulch Experimental Watershed (WGEW) near Tombstone, Arizona. Within much of the root zone (to 30 cm depth), infiltration was not significantly different under versus between shrubs, and the under: between infiltration ratio was not related to pulse size or intensity. However, root-zone soil moisture was significantly higher between shrubs than under shrubs. The soil moisture measured at the surface (at 5 cm depth) was not consistently different under and between shrubs, but the soil moisture measured at depths of 15 and 30 cm were both significantly higher between shrubs than under shrubs. Considering mechanisms that explain the interaction between plants and soil moisture, we found no differences in infiltration, evaporative losses, and surface soil moisture in locations under and between shrubs. This led to the conclusion that lower root-zone soil moisture under shrubs was due largely to greater root density under shrubs than between shrubs. This study adds to the understanding of the impact of precipitation patterns on infiltration and soil moisture in shrub-dominated sites and the potential for vegetation change in arid and semiarid lands.