Changes in the moisture contribution over global arid regions

Arid regions have deficient precipitation, understanding the sources and transportation of moisture for precipitation are crucial. This study examined the major moisture contributions for global six arid regions, which are classified as inland arid region (China-Mongolia) and coastal arid regions (North Africa, West Asia, West United States, South Africa, South Africa and Australia). Results indicated that, the moisture for precipitation in coastal arid regions originates mostly from the ocean, which is influenced by the general circulation, particularly by the sinking branch of the Hadley cell. For inland arid region (China–Mongolia), the surrounding mountains supply more than 150 mm of moisture in wet months due to the ablation of glacial and snow melting. In arid regions, the moisture for precipitation is mostly contributed by advection of large-scale circulation, while the contribution of local moisture recycling is secondary. The moisture available for precipitation in wet and dry months depends on the general circulation. Moisture transportation in wet months is 10 times more than that in dry months, and the moisture sources differ greatly in wet and dry months. In both wet and dry months, the external moisture transported into arid regions has significantly decreasing trend during the period 1990–2019. The decreasing trend of precipitation recycling ratio in arid regions are greater than that in the globe. The decreased precipitation and moisture in arid regions suggest a potential drying trend.