The asymmetric impact of abundant preceding rainfall on heat stress in low latitudes

Abstract

In addition to high temperature, high humidity can have significant consequences on thermal comfort of human beings. The co-occurrence of high temperature and high humidity (so-called 'oppressive hot days') often results in heat stress events, but the extent to which it is affected by preceding surface moisture has not been fully understood to date. In this study, we examine the relations between preceding 3-month standardized precipitation index (SPI) and the number of hot days indicated by the surface air temperature (NHD-Tx) and the wet-bulb globe temperature (NHD-Wx) that combines both temperature and humidity in the hottest month in low latitudes. Results show that, in contrast with the negative correlations between SPI and NHD-Tx, which are associated with the previously reported precipitation deficit-temperature feedback, significant positive correlations between SPI and NHD-Wx are found in some low latitude areas. The probability of above-average NHD-Wx could be ∼30% higher after wet conditions than that after dry conditions in areas like southern South America, some parts of Africa, and West Asia. Hotspot analyses further show that abundant preceding rainfall has an asymmetric impact on oppressive hot days by favoring more above-average NHD-Wx. Our analyses imply that a local feedback may exist between surface moisture and oppressive hot extremes, via which the unbearable heat stress over some parts of the tropics is modulated, controlled, and/or caused by changes in the preceding near-surface humidity/soil moisture. The spatially heterogeneous patterns of the relations between preceding rainfall and heat stress confirm the precipitation deficit-temperature feedback in many areas and reveal the coexistence of surface moisture-oppressive heat stress in several low latitude areas. We emphasize the necessity of considering both feedbacks for a better understanding of the distinct roles of preceding rainfall in the consequent development of heat stress in low latitudes.

Summer hot extremes and antecedent drought conditions in Australia

“…(2017) and Liu et al . (2019) used the index NHD and were able to identify significant correlations in the southwest, using different datasets.…”

“…This analysis was performed for the austral summer, which includes the months from December to February, and for the periods 1979–2019 and 1950–2019. The use of these time periods allowed us to assess changes in the relationship between SPEI and NHD/NHN that may have occurred, while at the same time compare our results to previously published works that have used similar time periods (Mueller and Seneviratne, 2012; Herold et al ., 2016; Holmes et al ., 2017; Liu et al ., 2019). The correlation between SPEI and the extreme temperature indices NHD and NHN was computed for the periods 1979–2019 and 1950–2019, using a 2‐tailed Spearman's rank correlation coefficient, and a level of significance of 0.1.…”

“…The relation between drought and extreme heat events, particularly the effect of antecedent drought conditions on the occurrence of temperature extremes has been identified in several world regions (Mueller and Seneviratne, 2012;Liu et al, 2019), such as the Mediterranean basin (Russo et al, 2019;Ribeiro et al, 2020a), China (Hao et al, 2017;Zhang et al, 2019) and Australia (Perkins et al, 2015;Herold et al, 2016;Holmes et al, 2017). Previous studies have highlighted the role of spring precipitation deficits, increased solar radiation, and warming in amplifying the high-temperature anomalies in extreme summers due to soil moisture depletion (e.g., Fischer et al, 2007a;Barriopedro et al, 2011) and worked on that assumption to analyse ecosystems productivity (e.g., Bastos et al, 2021) and fires (e.g., Abram et al, 2021;van Oldenborgh et al, 2021).…”

Concentrated and Intensifying Humid Heat Extremes in the IPCC AR6 Regions

“…Regions with differences, however, are notable and motivate an exploration of potential drivers. Previous studies have suggested that humidity can be important, especially for arid regions, through moisture advection and/or soil moisture effects due to either irrigation or precipitation (Kang & Eltahir, 2018; Krakauer et al., 2020; Liu et al., 2019; Mishra et al., 2020; Monteiro & Caballero, 2019; Pal & Eltahir, 2016). Our results corroborate this hypothesis and provide fresh evidence for it.…”

Reductions in Labor Capacity from Intensified Heat Stress in China under Future Climate Change

“…Heat stress often brings thermal discomfort or heat injury to human bodies when people are exposed to ambient air [1]. Heat stress has significantly increased during the past decades [2][3][4] and will be intensified in many regions of the world in the future [5,6].…”