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This study aims to understand how well regional climate models (RCMs) reproduce the observed characteristics of droughts based on the standardized precipitation evapotranspiration index (SPEI) over East Asia. While RCMs from CORDEX East Asia have been evaluated in terms of the mean and extreme values of precipitation and air temperature in the literature, their performance based on drought characteristics has not been revealed. Therefore, we investigate the temporal characteristics, such as the trend and stationarity, and other drought measures, such as the drought frequency, duration, severity and spatial extent, to determine how well these factors are captured and how they vary among the different models, including four RCMs, their ensemble mean and a driving general circulation model (GCM). The results are compared to a 26‐year observational dataset (1980 to 2005) from APHRODITE. Based on our analyses of the results, the specific findings are as follows. First, based on Mann–Kendall (MK) trend tests, the SPEI shows decreasing trends over the northern part of the domain and no trends in other regions, and these tendencies are captured by a limited number of RCMs. Notably, these trends were not captured by the ensemble mean of RCMs. Second, based on the Phillips–Perron stationarity test, stationarity is dominant in most regions based on both the observations and the RCMs. Third, the frequency decreases with increasing duration in all regions. This tendency is generally captured in the models to varying extents. Fourth, the drought severity decreases with increasing duration in all cases, as expected. However, the drought severity diverges markedly among the RCMs. Finally, estimates of the spatial extent using the RCMs are generally accurate in wet regions but inaccurate in dry regions. Furthermore, the spatial extents of the droughts diverge among the RCMs, and the models fail to accurately capture drought events with large spatial scales.

Abstract. This study aims to understand how different reference periods (i.e., calibration periods) of climate data used to estimate drought indices influence regional drought assessments. Specifically, we investigate the influences of different reference periods on historical drought characteristics, such as the trend, frequency, intensity and spatial extent, using the standardized precipitation evapotranspiration index (SPEI) with a 12-month lag (SPEI-12), which was estimated from the datasets of the Climate Research Unit (CRU) and the University of Delaware (UDEL). For the 1901-1957 (P1) and 1958-2014 (P2) estimation periods, three different types of reference periods are used to compute the SPEI: P1 and P2 together, P1 and P2 separately and P1 only. Focusing on East Asia, Europe, the United States and West Africa, we find that the influence of the reference period is significant in East Asia and West Africa, with dominant drying trends from P1 to P2. The reference period influenced the assessment of drought characteristics, particularly the severity and spatial extent, whereas the influence on the frequency was relatively small. Finally, self-calibration, which is the most common practice for indices such as the SPEI, tends to underestimate the drought severity and spatial extent relative to the other approaches used in this study. Although the conclusions drawn in this study are limited by the use of two global datasets, they highlight the need for clarification of the reference period in drought assessments to better understand regional drought characteristics and the associated temporal changes, particularly under climate change scenarios.

The problem of finding a unique flame propagation rate for a given distribution of surface heat flux is solved analytically for three solid fuel geometries (i) finite slabs, (ii) finite rods (iii), semi-finite fuel bed. The solutions cover a range of fuel thicknesses from the thermally thin limit to the thermally thick limit. The effect of longitudinal heat conduction within the fuel is considered and found to become important as the fuel thickness increases. Experimental results on the downward burning of PMMA sheets are presented for the flame spreading velocity and preheat distance. The preheat distance is found to become independent of fuel thickness for I >0.25 em. A combination of the analytical and experimental results leads to a determination of the surface heal transfer parameters.