On the convenience of the use of seasonal and monthly climatic indices in correlation studies

Abstract

Moderately extreme rainfall is usually characterized by a set of standardized indicators, the ETCCDI precipitation indices, useful to compare climate changes on a global scale. These indices quantify information to reflect some aspects of the state of the environment by aggregating data in annual amounts, simplifying the study of complex phenomena. There is extensive use of these annual standardized indices in many fields, such as agriculture, human health and water resources. In particular, a complex correlation between rainfall annual indices and pollination/sporulation parameters can be observed, being useful to describe, in a global way, their joint variations and trends over time. However, a direct cause-effect relationship cannot be established due to the time limitations of the pollen and fungal spore release seasons. To investigate this possible causality, the modification of the standardized annual indices by calculating them only for the autumn or winter before the release seasons, or even for a specific previous month, can be essential.