Near-Surface Above- and below-Ground Measurements of Soil Evaporation.

Evaporation (E) constitutes a significant fraction of water loss from arid soils, especially in sparsely populated landscapes. We measured and compared E using three separate technologies in a semi-controlled facility to better understand the benefits and limitations. The technologies included three-wire heat pulse (TPHP) probes installed to measure water loss at 12 mm increments down to 48 mm depth; a vertical transect of humidity and temperature sensors installed at 50, 100, 250, and 500 mm above ground surface; and a weighing lysimeter with a resolution of ~0.02 mm of water. Measurements were taken intermittently over a period of approximately 2 years, spanning winter rainy and summer dry seasons, to capture a wide range in soil E. The results showed strong correlation in the water mass balance using measurements from the TPHP and lysimeter (r>0.90) during winter periods, but the correlation decreased in the summer as the E rate decreased. Summer and winter E rates were also estimated using an energy balance approach using humidity and temperature data from the vertical transect, augmented with net radiation and soil heat flux. The overall results will be discussed and contrasted.