Date of Final Oral Examination (Defense)

8-2011

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Civil Engineering

Department

Civil Engineering

Major Advisor

Venkataramana Sridhar, Ph.D.

Abstract

This study investigated the interaction of land-surface processes and vegetation in both natural ecosystems and irrigated agricultural lands in a semiarid region using the Noah land surface model (LSM) in combination with the Weather Research and Forecasting (WRF) Model. This study was conducted in the semiarid Snake River plains of south central Idaho comprising of both natural vegetation and agricultural lands. This area is characterized by warm, dry summers with irrigation being the main moisture source during the growing season. In order to properly represent the conditions of agricultural lands and also to investigate the effects of irrigation on land-surface processes, an irrigation algorithm was introduced into the existing LSM.

Land-atmosphere feedbacks of natural vegetation were investigated through the complementary relationship between the actual evapotranspiration (ET) and the potential evapotranspiration. Results from a coupled version of the LSM enabled this research to study the effects of land surface on near-surface atmospheric properties, potential air temperature, and specific humidity.

The results from this study proved the importance of including irrigation in LSMs over agricultural lands in semiarid regions. Irrigation changed the surface energy budget partitioning by increasing latent heat flux and reducing sensible heat flux. Vegetation has a greater role in partitioning the surface energy balance components. Surface cooling effects were observed through irrigation. There was a complementary behavior between LSM-simulated actual ET and potential ET computed from the North American Regional Reanalysis (NARR) data in natural vegetation during the moisture limiting periods. It was found that the sensible heat has been underestimated for croplands by the uncoupled LSM when verified against the control runs from WRF. The impact of coupling on natural vegetation was low compared to croplands and forests showing that, in croplands and forests, feedback effects of land surface to the atmosphere were more important. Land surface has significant influences on the lower atmosphere and the evolution of the planetary boundary layer.

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