Monitoring the Ice Phenology of Qinghai Lake from 1980 to 2018 Using Multisource Remote Sensing Data and Google Earth Engine

Lake ice, one of the most direct lake physical characteristics affected by climate change, can reflect small-scale environmental changes caused by the atmosphere and hydrology, as well as large-scale climate changes such as global warming. This study uses National Oceanic and Atmospheric Administration, Advanced Very High Resolution Radiometer (NOAA AVHRR), MOD09GQ surface reflectance products, and Landsat surface reflectance Tier 1 products, which comprehensively used RS and GIS technology to study lake ice phenology (LIP) and changes in Qinghai Lake. Over the past 38 years, freeze-up start and freeze-up end dates were gradually delayed by a rate of 0.16 d/a and 0.19 d/a, respectively, with a total delay by 6.08 d and 7.22 d. The dates of break-up start and break-up end showed advancing trends by −0.36 d/a and −0.42 d/a, respectively, which shifted them earlier by 13.68 d and 15.96 d. Overall, ice coverage duration, freeze duration, and complete freeze duration showed decreasing trends of −0.58 d/a, −0.60 d/a, and −0.52 d/a, respectively, and overall decreased by 22.04 d, 22.81 d, and 9.76 d between 1980 and 2018. The spatial pattern in the freeze–thaw of Qinghai Lake can be divided into two areas; the west of the lake area has similar spatial patterns of freezing and ablation, while, in the east of the lake area, freezing and ablation patterns are opposite. Climate factors were closely related to LIP, especially the accumulated freezing degree-day (AFDD) from October to April of the following year. Furthermore, freeze-up start time was more sensitive to changes in wind speed and precipitation.

P1921Impact of cryoballoon freeze duration on long-term durability of pulmonary vein isolation in atrial fibrillation: insights from Re-mapping procedures (the ICE Re-map study)

Background Second-generation cryoballoon (CB2) represents a powerful pulmonary vein isolation (PVI) tool. Recently, the randomized time-to-effect guided (ICE-T) CB2 strategy targeting a 240s single freeze demonstrated fast and efficient PVI. To further optimize safety and efficacy, a shortened 3min freeze duration has been suggested but PVI durability remains unclear. Methods Between May 2013 and December 2017 all CB2 ablations followed the ICE-T concept (target-freeze: 240s or 180s). Patients undergoing a second procedure for arrhythmia recurrence were analyzed. Two groups were defined based on the index freeze duration (group 240s vs. group 180s). In all repeat procedures a 3D left-atrial map was obtained. Durability of PVI and localization of conduction gaps were compared. Results A total of 106/788 (13%) patients underwent a second procedure (group 240s: 80/604 vs. group 180s: 26/184) after a mean of 377 days. There was no difference regarding PV occlusion and time-to-isolation in the index procedure between two groups. No major complications occurred. During the second procedure significantly more patients demonstrated durable isolation of all PVs in group 240 (61% vs 35%, p=0.02) along with a significantly increased rate of PVI durability (88% vs. 69%, per vein, p<0.001). Left sided PVs did significantly benefit from 240s freezes (reconnection LSPV: 6% vs 27%, p=0.004, LIPV: 14 vs. 39%, p=0.006). Conclusions The ICE-T strategy is associated with a high rate of durable PVI in patients with arrhythmia recurrence. Target freeze duration of 240s vs. 180s is associated with significantly increased lesion durability, particularly at left sided PVs, without increasing complications.

Interdecadal Changes in the Freeze Depth and Period of Frozen Soil on the Three Rivers Source Region in China from 1960 to 2014

On the basis of observed soil freeze depth data from 14 meteorological stations on the Three Rivers Source Region (TRSR) in China during 1960 to 2014, trends in the freeze depth, first date, last date, and duration of frozen soil were analyzed, together with other meteorological variables, such as air temperature, snow depth, and precipitation, observed at the same locations. The results showed the following. (1) A continuous, accelerated decreasing trend in freeze depth appeared in the TRSR during the 1985–2014 and 2000–2014 periods, compared with that during the 1960–2014 period. (2) The freeze first date had been delayed and the freeze last date had been advanced significantly. The advanced trends in freeze last date were more significant than the delayed trends in freeze first date. The freeze duration also experienced an accelerated decrease. (3) The freeze depth and period were strongly affected by air temperature, thawing index, and soil moisture (precipitation), but not by snow. The freeze depth, freeze first date, freeze last date, and duration also influenced each other. (4) These decreasing trends in freeze depth and duration are expected to continue given the increasing trends in air temperature and precipitation in this region.

Long-Term Changes in Ice Phenology of the Yellow River in the Past Decades

The authors quantitatively describe the changes in the characteristics of ice phenology including the flow rate and freeze/breakup dates of the Yellow River based on observations of the past 50 yr. In both the upper and lower reaches of the Yellow River, increasing temperature delays the freeze date and advances the breakup date, thus decreasing the number of freeze days and the expanse of river freeze. From 1968 to 2001, the freeze duration has shortened significantly by 38 days at Bayangaole and 25 days at Sanhuhe, respectively. From the early 1950s to the early 2000s, the changes in freeze and breakup dates have shortened the freeze duration in the lower reach of the Yellow River by 12 days. The flow rate has reduced from 500 to 260 m3 s−1, and the expanse of river freeze has also decreased significantly by about 310 km. In addition, in the lower reach of the river, the location of earliest ice breakup has shifted downstream significantly in the last 50 yr, although the location of earliest freeze exhibits little change.