Bu yazımızın birinci kısmında; «yağış etkinliğinin önemi» üzerinde durulmuş ve geçmiş yıllarda bu konu ile ilgili olarak teklif edilen formüller kısaca tanıtılmıştır. İkinci kısmında ise; Türkiye şartlarına göre «yağış» ile «günlük maksimum buharlaşma» miktarını (mm) esas alan «yeni bir yağış etkinliği indisi» teklif edilmiştir.Şunu önemle belirtmek isteriz ki, bu yazımızda takdim ve teklif edilen «yeni yağış etkinliği formülü», yağış ile potansiyel evapotranspirasyon arasındaki ilişkiyi «objektif» bir şekilde yansıtmaktadır. Çeşitli amaçlara yönelik olan formül, basit matematiksel işlemlere dayanmaktadır. Yardımcı formüllerinin bulunuşu nedeniyle uygulanma alanını genişletici özellik taşımaktadır. Aynca, basit matematiksel işlemleri bile en aza indirmek amacıyla, muayyen devrelere ait «indis» değerlerinin kolaylıkla elde edilebileceği şekilde, oldukça hassas bir «genel nomogram» hazırlanmıştır  

In this study, firstly, the importance of the precipitation has been evaluated and the others precipitation indices have been examined, shortly; and secondly, a new precipitation efficiency index has been proposed depending upon precipitation and dally maximum evaporation according to Turkey’s conditions. The basis of the new formula were given below:In order to establish the water deficiency relating with during the vegetation period and yearly, the new correlations has been submitted and its application has been carried out on the agriculture. In addition to this, same method has been applied on the afforestation activities in order to determine the water supply, in these applications climatic data were obtained by the 57 meteorological stations.It is indicated that in the new index relationships between the precipitation and evaporation are clearly emphasised, in other words, positive results could obtain in the applications both the agricultural activities and the classification of the vegetation. On the other hand, the new formula depends on the basic mathematical operations and also a nomogram was presented in order to devise the indices relating with identical periods (Fig. 4).According to results, which were resulted in the application of the new formula, the semiarid area covers an area of 17.54 percent of the total land of Turkey, and the other figures are as follows: Subhumid area is nearly 50.88 percent, humid land is about 26.32 percent, and perhumid area is about 5.26 percent. This position can be see on the yearly precipitation efficiency map of Turkey made by the new formula (Fig. 1).in order to classify the relationships between the climatic types and vegetation formations, the precipitations and daily maximum evaporations has hnlance As far as I know, that Is why the Leen into consideration to reveal balance.  As far as I know that is why the proposed new index can be reveal the useful data determining the precipitation efficiency. This balance could not into calculation the other indices which has been proposed to determine the precipitation efficiency so far.