Decreasing changes of climatic elements such as: daily precipitation, weekly precipitation, seasonal precipitation and annual precipitation can be toward to drought phenomena. The recognition it and planning for passing it, could be decreasing of disasters, because create of drought is slow but it effects is very damages. The aim of this paper is descriptive analyze and it type of research is applied research with uses of filed work and obtains of tree ring desk and comparison precipitation in statistical at study time (1995-2003) in Soome-e-Sara of Gilan province by a research project. Result of this paper has shown that drought or deficit of rain has been direct relationship with growth tree ring index (TRI). Diameter increment in (Populus Deltoids) Poplar-trees and relationship between annual precipitation and annual tree ring index has been with correlation r=0.662 (a=5%), but without view of year happen this correlation is r=0.88. Changing of decreasing precipitation from 1200 millimeter to 800 millimeter (Drought) accompanying has been with 2.3 millimeter decreasing of Tree ring indexed in the time of study period. This factor has been accompanying with high destroy in area. Increasing of studying and look at to suggestion ways of this paper could be benefits.