Climate-Based Representations of Summer Rainfall in Illinois

Abstract

Historical (1901?85) summer (June?August) rainfall data in central Illinois were used to construct three typical rain conditions: one representing the typical dry summer (based on the driest 20% of the summers of the past 85 years), a typical wet summer (from the 20% wettest), and the near-average summer rainfall conditions (the 20% nearest the long-term average). Monthly rain totals for each type were established first, then daily rain frequencies were used to define all individual rain day amounts, and historical rain-day amounts by date were used to assign rain days to dates throughout the three types of summers. In-day conditions relating to rainfall rates, time of rain, and durations were constructed for each day of rain. The resulting three summer rainfall conditions are being used to guide applications of water onto agricultural test plots (protected from natural rains) to measure crop yield effects from weather modification but the approach and system could serve other applications like effects of climate change.