This study compares two methods for evaluating precipitation effects on wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) yield, which have been cultivated for 30 years under two different climate conditions (semi-arid and Mediterranean). The distribution and amount of precipitation were indexed and their relationship with the corresponding crop yields (1984–2013) was investigated. The concen- tration index (CI), i.e. the contribution of the days of greatest precipi- tation to the total amount of precipitation, was also calculated as an alternative approach. Both methods were used to analyze the whole crop growing season, from planting to harvest, and for two critical growth stages, germination and anthesis. It was observed that there was a significant correlation between yield and the average daily precipitation (ER; rwheat1⁄40.74 and rbarley 1⁄4 0.75) during the whole growing season, irrespective of the crop type, whereas there was no significant impact on crop yield due to the non-uniformity of precipi- tation distribution (UR). However, when a critical stage like anthesis was evaluated over a shorter period, a significant correlation between UR and crop yields (rwheat1⁄40.56 and rbarley1⁄40.64) was found. The results indicated that these indexes are very effective for predicting crop yields based on their association with final yield within critical growth stages. In addition, it was also found that a proposed model using both indexes (ER and UR), with high correlation (r1⁄40.84) can be very effective in estimating crops performance. The results also showed that the sensitivity of crop yield to the uniformity of precipitation during the critical growth stages was lower than when the whole growing season was considered. The CI index was less effective in reflecting the distribu- tion of precipitation in the semi-arid and Mediterranean conditions compared with the UR.

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