There were serious shortfalls in this year's grain production due to the drought.

shortfalls 是名词 shortfall 的复数形式。shortfall 由 short（短缺的）和 fall（下降）组成，字面意思是"短缺下降"，引申为"不足、短缺"的意思。在这里指粮食产量未能达到预期水平而出现的短缺情况。