Variability of temperature extremes in the Yellow River basin during 1961–2011

Abstract

The variability of temperature extremes was widely discussed in the past few decades worldwide associated with global warming, which impacted the hydrological cycle and energy balance. In this study, on the basis of daily maximum and minimum air temperature at 62 meteorological stations in the Yellow River basin, the changes in 13 indices of temperature extremes recommended by the ETCCDI were investigated in the Yellow River basin from 1961 to 2011. Both cold extremes and warm extremes showed a warming trend, with a large proportion of stations having statistically significant trends for most temperature indices. Because of a faster increase in minimum temperature than maximum temperature, diurnal temperature range (DTR) has decreased by −0.07 C°/decade. For cold extremes indices, i.e. coldest night (TNn), coldest day (TXn), cool nights (TN10p), cool days (TX10p), frost day (FD) and icing day (ID), the trends during the period of 1961–2011 were 0.23 and 0.22 C°/decade, and −5.23, −3.31, −2.61 and −3.16 days/decade, respectively. For warm extremes, i.e. warmest night (TNx), warmest day (TXx), warm nights (TN90p), warm days (TX90p), warm spell duration index (WSDI) and growing season length (GSL), the trends were 0.20 and 0.21 C°/decade, and 3.80, 3.26, 2.93 and 4.81 days/decade, respectively. In general, the indices have the largest change magnitudes in the arid and semi-arid sub-regions, followed by the high-elevation sub-region, and the indices have the smallest changes in the eastern monsoon sub-region. Relationships between the changes in the temperature extremes and the changes in the large-scale atmospheric circulations were studied. Results show that the changes in the temperature extremes were consistent with the changes in the area and strength of Northern Hemisphere Subtropical High (NHSH) and Northern Hemisphere Polar Vortex (NHPV).