THE INFLUENCE OF IRRIGATION ON THE ENERGY BALANCE AND THE CLIMATE NEAR THE GROUND

Abstract

A theoretical analysis is presented of the influence of irrigation on temperature and humidity of the lower air layers and on the energy balance of the surface. Starting from meteorological data for the dry land (averaged over periods of a few days or longer), the average temperature and moisture profiles in an irrigated area are calculated as functions of the distance downwind from its boundary. The principal simplifying assumption in the analysis is that for each height the eddy diffusivities should have the same values in the irrigated and non-irrigated areas. The theory is applied to and illustrated by measurements of climatic differences between irrigated and non-irrigated pastures in the Australian Riverina. Experimental results of other investigators are briefly discussed. The present developments have led to a theoretical estimate, taking advective energy into account, of the potential evaporation rate for irrigated areas of limited extent on the basis of standard meteorological data for the dry land. The influence of advection decreases rapidly with increasing distance downwind. Under summer conditions in the Australian Riverina, it is considerable up to distances of about 1 km.