430 THE FUTURE OF ARID LANDS 
condensation nuclei (including giant hygroscopic nuclei) by 
studies of the chemical composition of precipitation and by the 
ooo. of cloud surveys. 
» AL fNOIRS vigorous study of all possible aspects of periodic 
ce seeding is imperative. 
10% Dreger: knowledge of nucleation properties of silver iodide 
as affected by the methods of generation and dispersal is inade- 
quate. Further studies, with particular reference to the decay of 
the nucleating activity of silver iodide with increasing time of 
exposure in the atmosphere, are recommended. 
13. Closer integration of the sciences of climatology and hy- 
drology can be fostered through better exchange of information 
and collaborative analyses aimed at improving joint methodology. 
The lack of such collaboration between climatologists and hy- 
drologists has contributed in the past to inadequate estimation of 
available water resources in some arid-zone projects. 
Recommendations 17, 19, 25, and 29 are also applicable. 
Hydrology, Geology, and Soils 
14. The importance of ground water in arid zones calls for 
continued research on the following aspects of this subject: (1) 
methods of exploration and estimation of the volume of ground 
water bodies; (11) methods of increasing ground water recharge 
and of estimating rates of recharge; (111) the relation of vegetation 
and other biological factors to ground water recharge; (iv) the 
geomorphological aspects of the occurrence and chemistry of 
ground water. 
15. The precipitation occurring on drainage basins should not 
be regarded in terms of utilization for irrigation alone, and more 
consideration should be given to planning for the beneficial use of 
water that is not reaching points of downstream use. 
16. Continued study is needed of the factors and practices 
modifying soil structure under various land-use practices, such as 
grazing, dry land farming, and irrigation farming, recognizing the 
importance of soil structure and its maintenance in relation to 
permeability and to prevention and abatement of erosion. 
17. The work of hydrologists and climatologists would benefit 
