Increasing concern about the environment has resulted in a greater need for improved knowledge of precipitation for the solution of water resources problems. A specific example of such a need is the recent world-wide research in development of hydrologic models for continuous synthesis of stream flow, the success of which will be ultimately limited by the reliability of the n-unary input function, precipitation. Much of the precipitation research during the 1967–1970 period has been concerned with errors in measurement and development of better methods for measuring areal and temporal distribution of precipitation.