Abstract
Precipitation phase is expected to shift from solid to liquid with temperature rising, which would in turn bring challenges to regional water resource management. Although in recent decades, consistent decreasing trends in the ratio of snowfall to precipitation rate in a warming climate have been found across multiple regions, a global view of the trends in the precipitation partitioning has not been established. In this study, we investigated the global trends of annual rain and snow frequency of occurrences and the ratio of number of snow events to number of precipitation events (SE/PE ratio) using land station and shipboard synoptic present weather reports from 1978 to 2019. Results show that when averaged over all qualified land stations and over the shipboard reports, both the annual rain frequency and snow frequency decrease over the 42 years. Over both land and ocean, the averaged SE/PE ratio has a significant decreasing trend. Moreover, the trend of SE/PE ratio shows a strong latitudinal dependence. At the mid- and low latitudes in the Northern Hemisphere, the SE/PE ratio has a decreasing trend. In contrast, at high latitudes, the SE/PE ratio has an increasing trend.
Highlights
Precipitation phase is expected to shift from solid to liquid with temperature rising, which would in turn bring challenges to regional water resource management
When averaged over the qualified land stations, significant decreasing trends are found both in the rain and snow frequency for the 42 years (Fig. 1a)
The snow frequency decreases at a rate of 0.034% year−1, while the rain frequency decreases faster at a rate of 0.046% year−1
Summary
Precipitation phase is expected to shift from solid to liquid with temperature rising, which would in turn bring challenges to regional water resource management. We investigated the global trends of annual rain and snow frequency of occurrences and the ratio of number of snow events to number of precipitation events (SE/PE ratio) using land station and shipboard synoptic present weather reports from 1978 to 2019. The ratio of snowfall days to precipitation days was found to decrease over the past century in Switzerland[19], with the decreasing trend stronger at lower elevations where temperatures were closer to the melting point Such correlation of S/P ratio with temperature was confirmed in multiple s tudies[14,19,20], and significant correlations with large scale climate patterns like the North Atlantic Oscillation and the PacificNorth American indices were o bserved[16,17]. Snow events are defined to include only solid precipitation with “ww” code from 70 to 79, 85 and 86; rain events include all liquid and mixed phase precipitation
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