The modification of climate near the ground by irrigation for pastures on the Riverine plain

Abstract

Methods are described and results reported of meteorological observations made during the irrigation seasons 1936–57 and 1957–58 at three stations in the Nanneella irrigation area (dimensions approximately 6 by 7 km²) and on a dry-land station nearby. The former stations are situated on irrigated pastures, whilst the latter is on a dry-land pasture. Irrigation gives rise to a decrease of air and soil temperatures and an increase of atmospheric humidity- near the surface of the earth. The magnitudes of these effects depend inter alia on the irrigation rate and the distance down wind in the irrigated area. In summer at an irrigation rate of approximately 0.3 cm/day the observed differences between the dry-land station and a station in the centre of the irrigation area amounted to: 1–2°C for air temperature at screen height (125 cm); approximately 10°C for soil temperatures (at depths of 5 and 30 cm); 5–10% for relative humidity at screen height; 0.5–1.5 mm Hg for vapour pressure at screen height. The differences quoted are for average values of the observed quantities taken over a period of 4 weeks. The observations are presented in more detail in graphical form.