Spatial and Temporal Variability in Positive Degree-Day in Western China under Climate Change

Guohua Liu,Xiqiang Wang,Rensheng Chen

doi:10.3390/atmos12040443

Abstract

Positive degree-day (PDD) indicates the accumulated positive temperature in a given time period; it directly relates to the melting of snow and ice, and it is a key parameter between global warming and cryosphere changes. In this study, we calculated the PDD based on the daily mean temperatures from 1960 to 2018 at meteorological stations, and we used measured and interpolated data to determine spatial and temporal distribution and changes in PDD in western China (WC). Results show that the mean annual, warm season, and cold season PDD values at 209 meteorological stations were 3652.2, 2832.9, and 819.3 °C, respectively. PDD spatial distribution in WC is similar to that of air temperature. In WC, PDD mainly ranged from 0 to 5000, 1000 to 4000, and 0 to 1000 °C year−1, respectively for annual, warm season, and cold season. From 1960 to 2018, the observed mean initial day of PDD moved forward by 8.3 days, and the final day was delayed by 8.2 days, with the duration expanding to 16.6 days; the trend in PDD reversed in the 1980s and the change rate in PDD for annual, warm season and cold season was 6.6, 3.8, and 2.7 °C year−1, respectively. Regionally, PDD increased in almost all areas; the high PDD advanced from south to north, east to west, desert to mountain, and low to high altitudes. The results also showed that the warming rate of PDD was lower in the cold season and in high-altitude areas, which was opposite to the observed temperature patterns, however, the non-linear relationship between PDD and mean temperature over a period of time is the main reason for this phenomenon. This study adds more details for the understanding of climate change in WC, and suggests that more attention should be paid to PDD in the study of cryosphere changes.

Highlights

Global warming since the last century is responsible [1,2] for a temperature rise that is especially noticeable in the middle latitudes of the northern hemisphere [3]
The mean initial date of Positive degree-day (PDD) moved forward by 8.3 days from 1960 to 2018 for all 169 stations, while the mean terminal date was delayed by 8.2 days and mean duration expanded to 16.5 days
This paper studied the spatial-temporal distribution of annual, warm season, and season PDD in western China (WC) from the 1960s to the 2010s

Summary

Introduction

Global warming since the last century is responsible [1,2] for a temperature rise that is especially noticeable in the middle latitudes of the northern hemisphere [3]. The warming rate in western China is lower than that in eastern parts of the country [5], the temperature increase in the arid region of northwestern China is significantly higher than the region’s average [6,7,8,9], and the climate regime has shifted from warm-dry to warm-wet [10,11]. Plateau in western China is affected by elevation-dependent warming [12,13,14], and the warming rate is significantly higher than that in the surrounding low altitude areas [15,16], especially in cold seasons [17,18,19,20]. A warming trend is expected to continue in this area in the near future [21]

Objectives

Results

Discussion

Conclusion