Abstract
This paper aims to analyse the distribution and temporal evolution of convective precipitation in the Mediterranean region of Spain. To accomplish this goal, we used 148 sets of 5-min rainfall rate data from the 1989–2015 period. The selected regions were the Júcar Hydrographic Confederation (CHJ) and the Internal Basins of Catalonia (CIC), which cover most of the autonomous communities of Catalonia and the Valencian Community (east Spain). The average 5-min intensity threshold of 35 mm/h and the β parameter, defined as the ratio between convective precipitation versus total precipitation in any period, were used to characterise convective precipitation. Convective episodes were categorised as “very convective”, “moderately convective”, and “slightly convective” based on the β value. After quality control, the series of 129 stations were clustered into homogeneous precipitation zones that also include β as one of the variables of characterisation. The results show that convective precipitation can contribute to total annual precipitation by up to 16% on average, but it is generated by a very small percentage of convective events (between 3% and 6% across all the stations) in comparison with the total number of rainfall episodes. In this sense, moderately convective events are the most common, with a predominantly unimodal monthly distribution of β, with summer the most convective season. Trends show a significant increase in precipitation, convective precipitation, and convective episodes in the CHJ. On the other hand, a positive trend of convective events is predominant in the CIC region, despite an overall precipitation decrease in the analysed period. These results are relevant given that extreme daily rainfall does not show a positive or significant trend, and they are in line with the impact of climate change on increased atmospheric instability and water vapour in the atmosphere. They highlight the need to work with sub-daily precipitation series in the case of the Mediterranean, which is mainly affected by flash floods.
Highlights
One of the main impacts of climate change appears to be an increase in heavy precipitation, as pointed out by the Clausius-Clapeyron equa tion (Alexander et al, 2006)
It shows the strong role played by the orography surrounding a warm sea, which characterises the Mediter ranean region, giving rise to high-impact atmospheric processes, as analysed in depth in Michaelides et al (2018)
The region of study is made up of two hydrographic basins, the In ternal Basins of Catalonia, managed by the Water Catalan Agency, and the Júcar, managed by the Júcar Hydrographic Confederation, with a total of 148 automatic rain gauges, that, after quality control, provided 129 series of 5-min rainfall rates. They were clustered in 19 homogeneous regions according to total precipitation and convective precipitation features
Summary
One of the main impacts of climate change appears to be an increase in heavy precipitation, as pointed out by the Clausius-Clapeyron equa tion (Alexander et al, 2006). Some works analyse the mechanisms that could be the cause of the increase in precipitation intensity associated with a warmer atmosphere (Lenderink and van Meijgaard, 2008; Berg and Haerter, 2013). Ye et al (1998), Chou et al (2012) and Lepore et al (2015) put the increase in convective precipitation behind the increase in CAPE (Convective Available Potential Energy, Weisman and Klemp, 1986) in response to warming and an increase in water vapour in the atmospheric boundary layer. Along the same line, Westra et al (2014) point towards an increase in the intensity in convective precipitation due to more water vapour, which intensifies the convective process. Wu et al (2019) have suggested that the strong Urban Heat Island (UHI) effect in large urban agglomerations is conducive to intensified hourly precipitation as a result of the individual and combined effects of land cover and land use changes, and an in crease in anthropogenic aerosol emissions
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