A physics-based statistical model to predict sub-hourly extreme precipitation intensification based on temperature shifts

We present a new statistical method for estimating extreme sub-hourly precipitation return levels that explicitly hinges on our physical understanding of the processes. The TENAX (TEmperature-dependent Non-Asymptotic statistical model for eXtreme return levels) model is based on two modules: (i) a magnitude module describes precipitation intensities using temperature as a covariate. It includes all the information about thermodynamics and local dynamics of the processes at a given temperature; (ii) a temperature module accounts for the distribution of daily temperature during rainfall events. Using the total probability theorem, the two modules are linked to provide a physics-based estimate of the marginal distribution of the precipitation intensities. Return levels are then estimated using a non-asymptotic method. Assuming that the physics of convection remains unchanged in the future (i.e., no change in the magnitude module) and that convection remains the dominant process, the TENAX model enables to project future sub-hourly precipitation return levels only based on the projected changes in daily temperature during rainy days. We will discuss the theory behind TENAX and show it can reproduce return levels with the same accuracy as more parsimonious non-asymptotic methods. We will additionally show that the model reproduces known properties of the extreme precipitation-temperature scaling relation for which it was not explicitly designed. Last, in hindcast, we will demonstrate that TENAX trained on observations of precipitation and temperature can well reproduce “future” unseen return levels only based on projections of daily temperatures. As projections of daily temperature from climate models are more readily available and accurate than those of sub-hourly extreme precipitation, TENAX could allow one to derive future sub-hourly return levels in any location globally where observations of past sub-hourly precipitation and daily near-surface air temperature are available.