OBSERVATIONS ON DETERMINATIONS OF DROUGHT-INTENSITY. 69 



OBSERVATIONS on the DETERMINATION op 

 DROUGHT-INTENSITY. 



By G. H. Knibbs, f.r.a.s., Lecturer in Surveying, 

 University of Sydney. 



[Read before the Royal Society of N. 8. Wales, August 2, 1899.~\ 



1 . Drought-intensity a definite function of measurable meteorological 



phenomena. 



2. Essential features of Mr. Deane's solution. 



3. Nature of the problem. 



4. Characteristically similar areas. 



5. Both quantity and rate of rainfall essential factors. 



6. Permeability. 



7. Laws of flow in permeable strata. 



8. Relation of rate of rainfall to saturation. 



9. Effect of slope of surface. 



10. Percolation into or through permeable strata when the interstices 



are full. 



11. Percolation when interstices are not filled. 



12. Exhaustion of moisture in soil by percolation. 



13. Exhaustion of moisture by evaporation. 



14. Solar radiation. 



15. Diffusion of aqueous vapour into the atmosphere. 



16. Effect of air temperature. 



17. Humidity and its influence. 



18. Effect of wind. 



19. General expression for degree of saturation. 



20. Necessity for the study of elementary cases. 



21. Graphs representing natural phenomena. 



22. Natural phenomena to be observed. 



23. General remarks. 



1. Drought-intensity a definite function of measurable meteoro- 

 logical phenomena. — The suggestive paper by Henry Deane, M.A., 

 M. Inst. C.E., entitled " Suggestions for depicting diagrammatically 

 the character of seasons as regards rainfall, and especially that of 

 drought," and read at the last meeting of this Society, is essentially 

 an attempt to derive, from the record of meteorological facts, a 

 graph representing a dependent phenomenon, viz., drought-intensity. 



