Use of seasonal dry and wet precipitation records to estimate the time of emergence (TOE) of changes in extreme precipitation anomalies

We use a method based on the detection of record breaking values in time series of seasonal precipitation anomalies to investigate the time of emergence (TOE) of changes in seasonal precipitation wet and dry extremes over 31 land regions of the world during the second half of the 20th century and the 21st century. The method is applied to the CMIP6 ensemble of 21st century projections for the SSP5-8.5 and SSP1-2.6 scenarios and to two observational datasets. Deviations of the number of detected records from the theoretical (reference) value expected from stationary climate conditions is indicative of trends in seasonal precipitation extremes. We find that, in response to climate warming, regions for which increased (decreased) mean precipitation is projected by the model ensemble, also experience a number of positive (negative) precipitation anomaly records much larger than the reference value. Also, the magnitude of changes in record anomalies is substantially larger than the changes in the mean. We then introduce an ad-hoc TOE criterion based on the ratio of actual to reference number of records (RatAR), and find that, in the SSP5-8.5 scenario, the TOE occurs as early as the late decades of the 20th century, and in most cases by the mid decades of the 21st century. A dominant projected increase in seasonal precipitation interannual variability also contributes to this result. Application of a similar criterion to the observation datasets yields TOE in the late 20th or early 21st century only for a small number of regional cases, for which, however, the direction of the change is mostly in agreement with the model projections. Our methodology can be useful in the assessment of impacts of seasonal drought-prone and flood-prone conditions and in studies of detection and attribution of seasonal precipitation extremes.