A frequent problem in the statistical analysis of data in environmental sciences is the synthesis of results obtained independently from various sets of data such as from different measuring points or from replicated experiments. Unlike their analysis separately, set' ultimate combined evaluation has often been given in descriptive terms. It is that critical final MW of data synthesis where meta-analysis comes in. Some principles of the method are presented and their usefulness is discussed. The approach is illustrated using previously published results on the hydrological effect of rainfall enhancement in Israel.