Towards Subdaily Rainfall Disaggregation via Clausius–Clapeyron G. BU ¨ RGER Universit € at Potsdam, Potsdam, and Freie Universit € at Berlin, Berlin, Germany M. HEISTERMANN AND A. BRONSTERT Universit € at Potsdam, Potsdam, Germany (Manuscript received 26 September 2013, in final form 5 January 2014) ABSTRACT Two lines of research are combined in this study: first, the development of tools for the temporal disag- gregation of precipitation, and second, some newer results on the exponential scaling of heavy short-term precipitation with temperature, roughly following the Clausius–Clapeyron (CC) relation. Having no extra temperature dependence, the traditional disaggregation schemes are shown to lack the crucial CC-type temperature dependence. The authors introduce a proof-of-concept adjustment of an existing disaggregation tool, the multiplicative cascade model of Olsson, and show that, in principal, it is possible to include tem- perature dependence in the disaggregation step, resulting in a fairly realistic temperature dependence of the CC type. They conclude by outlining the main calibration steps necessary to develop a full-fledged CC dis- aggregation scheme and discuss possible applications. 1. Introduction The environmental and societal importance of ex- treme precipitation is obvious, and so is the importance of obtaining sound projections of their future behavior under a warmer climate. Extreme precipitation events are usually understood as occurring within a time frame of a few days down to hours or even just a few minutes. The impact of an event is felt as flooding, on spatial scales that are (roughly) proportional to the scale of the dura- tion: the smaller a catchment, the shorter the time scale that is typical for bringing the heaviest damage (e.g., Bl€ oschl and Sivapalan 1995). As a consequence, rainfall events of subdaily duration (minutes to hours) present the most serious hazard for catchments with subdaily concentration time. This type of quick runoff concen- tration (flash flood) is typical for mountainous headwater catchments as well as urban catchments. Flash floods are particularly destructive because of high flow velocities, heavy debris loads, and a very low predictability (Collier 2007; Borga et al. 2011; Mueller and Pfister 2011). Unfortunately, such subdaily events are also charac- terized by a considerable lack of both observations and models, which likely represents two sides of the same coin (given the need for model verification). While high- resolution observations do exist, digitized versions, if they exist at all, are not as easily accessible as daily ob- servations. On the modeling side, considerable progress has recently been made with respect to weather forecasts. For example, Baldauf et al. (2011) employ a model with a grid resolution of only 2.8 km and an internal time step of 30 s. The dynamics of atmospheric convection are thus more realistically resolved and can be better pre- dicted, including the occurrence of heavy storms and flash floods. However, reliable estimates of the climate of extremes require much longer simulations that are (as yet) not available. Encountering scale gaps is not uncommon in climate modeling and will, for many readers, ring the bell of ‘‘downscaling’’ (see, e.g., Fowler et al. 2007). In the con- text of subdaily precipitation, downscaling usually ap- pears in the form of temporal disaggregation. There is a large body of literature on the temporal disaggregation of rainfall, going back to the 1970s and ranging from simple to very sophisticated approaches (see Koutsoyiannis 2003 for a comprehensive review). In all cases, a statistical model is sought that operates between aggregated (e.g., Corresponding author address: Gerd B€ urger, Universit€ at Pots- dam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany. E-mail: gbuerger@uni-potsdam.de JUNE 2014 B € URGER ET AL. 1303 DOI: 10.1175/JHM-D-13-0161.1 Ó 2014 American Meteorological Society