Abstract
Relative Humidity (RH) in the arid region of the Tarim Basin is crucial for many reasons. The Tarim Basin has experienced a tendency to become wetter in recent decades, and the RH there also shows an increase over the past decade. However, there has been little examination of these RH changes and especially the changes to the extremes. This study investigates the changes in extreme values and the probability density function (PDF) of summer RH using quantile regression during 2006–2018 to understand the possible reasons for the increase in the summer RH anomaly. We find that extremely high values of RH show a consistent significant increase, while extremely low values have no regionally consistent tendency. The overall average value of RH in the Tarim Basin becomes higher, contributed by the upper half of the PDF. To explore the physical mechanism for these changes, we examine the corresponding regional meteorological anomaly patterns. The patterns indicate that the anomalous southwesterly airflow at 500hPa brings ample moisture into the basin and the ground in the middle of the basin significantly cools down when an extreme wet event occurs, promoting the occurrence of the extreme high RH. In this process, the contributions of water vapor transport and temperature are of equal significance though with different relative timing. These corresponding regional meteorological patterns occur more often in the most recent decade, which coincides with the recent increase in RH extremes in this region.
Highlights
Relative humidity (RH), describing the distribution of water vapor in the atmosphere is of great importance for multiple fields
This study focuses on summer RH over the Tarim Basin, since the majority of the precipitation falls in summertime (Huang et al, 2015), and the increase in wetness is mainly concentrated in summer (Li et al, 2016; Peng and Zhou, 2017)
We find that values of 95th percentile RH for each summer averaged over the research area using ERA5 data agree reasonably well with those averaged from 19 meteorological stations (Fig. 6b)
Summary
Relative humidity (RH), describing the distribution of water vapor in the atmosphere is of great importance for multiple fields. Some more observations indicate that in Northwest China, a large region including the Tarim Basin, the precipitation has increased and the climate has become wetter in recent decades (Shi et al, 2007; Han et al, 2019; Peng and Zhou, 2017; Wang et al, 2017; Chen et al, 2015; Li et al, 2016). It shows that most stations have a tendency towards higher RH, which matches the results in previous studies (Han et al, 2019; Peng and Zhou, 2017; Wang et al, 2017)
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