## 1 Introduction
Therefore, knowing how to effectively quantify the changes in drought characteristics, specifically for vegetation communities over the course of a growing season, will provide an important guidance for alleviating the vegetative drought risk and thus promoting human well-being. The vegetative drought risk is expected to increase in the future because drying trends over an extensive region of the world have increasingly been attributed, at least in part, to anthropogenic global warming [18]. However, the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR5) pointed out that the rate of warming over the period of 1998-2012 (0.05 \({}^{\circ}\)Cper decade) was significantly smaller than the rate calculated since 1951 (0.12 \({}^{\circ}\)C per decade) [19], which has become known as a \"global warming hiatus\" [20]. Because of its apparent contradiction with human-induced global warming theories, it has fueled much debate and many studies about its possible consequences and causes. For example, [PERSON] and [PERSON] [21] investigated changes in daily precipitation extremes from 1998 to 2013 and concluded that the global warming hiatus will further increase the contrast between wet and dry extremes. [PERSON] et al. [22] analyzed the long-term trend and variability of flash droughts across China and found that the increasing trend of flash droughts had tripled during the global warming hiatus period. In addition, [PERSON] et al. [23] combined satellite and atmospheric observations to isolate the main terrestrial carbon cycle processes and concluded that the reduced respiration induced by the warming hiatus had accelerated net terrestrial carbon uptake. [PERSON] et al. [24] used long-term satellite and FLUXNET records to examine vegetation phenology trends in the northern hemisphere before and during the warming hiatus. They concluded that the rate of spring and autumn phenology change had slowed during the warming hiatus. These studies have highlighted the fact that a slight change in the mean global temperature may have profound implications for the climate system and the response of vegetation. In addition, a number of factors could have contributed to the recently observed hiatus in global warming, including changes in radiative forcing, anthropogenic radiative forcing, deep ocean heat uptake, and internal variability of the climate system [20; 25; 26; 27; 28]. However, other studies have noted that the warming hiatus is not a worldwide phenomenon but rather is mainly due to exceptionally cold events over continents in the northern hemisphere during boreal winter [29; 30]. This confluence of considerable impacts and controversial conclusions about the warming hiatus raises several questions, such as (1) whether the increasing trend of the growing season temperature, which has more to do with the growth of vegetation than the global mean temperature, had also stalled or even reversed in vegetation areas of the northern hemisphere after 1998; (2) whether the hydrological cycle in vegetation areas had decelerated during this global warming hiatus period; and (3) how the drought characteristics might have changed in vegetation areas of the northern hemisphere before and after the critical time point of 1998. To address these issues, we first estimated the mean vegetation phenology, including the dates of the start of the growing season (SOS) and end of the growing season (EOS), on the basis of 34 years of NDVI3g (third-generation normalized difference vegetation index (NDVI)) data. We then further identified the length of the mean growing season in each pixel of the vegetation zone in the northern hemisphere.