Climate-growth analysis using long-term daily-resolved station records with focus on the effect of heavy precipitation events

Oak tree-ring series contain detailed information regarding climate variability for centuries to millennia. Such reconstructions are compiled with the use of climate response functions that are typically based on monthly precipitation or temperature data sets. We present an approach using a MATLAB® script and long-term daily precipitation and daily mean temperature records to evaluate intervals with daily resolution of radial growth sensitivity and to determine the effect of heavy precipitation events in the Mainfranken region (southern Germany). This allows improved insights into tree-ring response for local climate reconstructions. Annual radial stem growth is highly sensitive to total cumulative precipitation during the current year spring-summer period, but less sensitive to daily mean temperature. Response analysis reveals better results to precipitation records, when (very) heavy precipitation events are omitted (April 14-July 18, R2 = 0.31, p < 0.01). Temporal sensitivity analysis of total ring width (TRW) to precipitation response within nine sub-periods revealed that the length of the sensitive intervals stretch between 41 to 141 days, depending on the period investigated. Our study shows that annual radial growth of oak trees is mainly affected by daily precipitation sums (DPS) of less than 10 mm. In contrast, heavy rainfall events do not influence radial increment significantly, but may substantially increase the total precipitation sum of the growing season. We propose that oaks in the Mainfranken region contain low to moderate information in their tree rings regarding heavy precipitation events. Furthermore, we conclude that a disordered sensitivity of TRW to precipitation during the past three to four decades is caused by drought climatologies, increased sulfur dioxide emission in the study area as well as by changes in diurnal temperature range. Thus, climate response functions for hydroclimatic reconstructions may only be developed until the 1970s.