Short-Term Daily Cycles and Dew Formation: The tree’s local sensors captured strong daily swings in weather. Each day, solar radiation climbed from 0 W/m² pre-dawn to around 400–480 W/m² near noon, driving air temperatures up from sub-freezing nights to midday highs. For example, on March 1 the air warmed from –5.0 °C at dawn to 11.1 °C by 13:15. As temperatures dropped after sunset, humidity rose toward saturation (vapor pressure deficit fell to ~0 kPa), causing dew to form on the tree. Early on March 1 (around 02:00–08:00), the leaf wetness sensor recorded up to 15 minutes of wetness per 15‑min interval – indicating the tree was coated in dew/frost through the night – even though no rainfall occurred. These daily patterns (cold, dry mornings followed by sunny warming and nocturnal dew) illustrate the periodic rhythm the tree experienced in late winter.
Sharp Freeze–Thaw Swings: The period saw a rapid temperature whiplash that would impact the tree’s physiology. After one of the coldest nights on February 25 (minimum –12.1 °C at 04:45), a pronounced thaw set in a few days later – by March 1 afternoon it reached +11.1 °C, a swing of over 23 °C in under a week. This freeze–thaw cycle can stress the tree: frozen soil and trunk tissues on Feb 25 would have thawed and expanded by Mar 1. Notably, the soil/ground moisture remained negligible during the freeze (electrical conductivity stayed at 0.0 mS/cm), but once temperatures rose and rainfall followed, the sensor showed a jump in moisture. This suggests that earlier in the week the ground was locked by frost, and only after the thaw could water penetrate – a pattern confirmed when rain on Mar 5 finally spiked soil EC to 0.112 mS/cm as the ground absorbed water. Such abrupt transitions from deep freeze to spring-like warmth are a short-term phenomenon that can cause bark cracks and root stress, yet the tree endured this dramatic shift in stride.
Sudden Cold Front with Wind Gusts and Snow (Early Mar 3): A brief but intense weather event on March 3 tells a dramatic story. Just before dawn, at 07:30, the tree was hit by an Arctic front – the station recorded a 17.2 m/s gust (the period’s peak wind, roughly 62 km/h). Winds picked up sharply (sustained ~5–6 m/s, gusting over 11 m/s through 08:15) as atmospheric pressure jumped by ~0.4 kPa in a few hours, signaling a fast-moving high-pressure surge. The air temperature at the time stayed around –2 to –3 °C, and at 08:15 a burst of precipitation fell at an intense 20.4 mm/h rate (snow squall conditions). In that 15-minute interval the gauge captured 0.34 mm water equivalent – likely a flurry of wet snow given the subfreezing air. Before this front, the tree had enjoyed a mild spell (near 7 °C on Mar 2); immediately after, daytime highs on Mar 3–4 stayed below 0 °C (only –1.8 °C on Mar 3). This abrupt shift from warmth to gale-force winds and snow illustrates the extreme end of short-term variability. The impact on the tree would be noticeable: the strong gusts could sway or prune weaker branches, and the sudden freeze following rain/snow could create an ice glaze on twigs, challenging the tree’s late-winter hardiness.
Cold Rain and Soil Moisture Recharge (Mar 5): A prolonged rain event on March 5 provided the tree with a much-needed moisture boost. Starting just after midday, precipitation fell steadily for about 5 hours, totaling ≈2.82 mm by early evening. At 13:15, a downpour began with 0.48 mm in 15 minutes (peak intensity ~12 mm/h), then tapered to lighter showers (0.1–0.3 mm each interval) through 18:00. Air temperature hovered at 1–3 °C during the rain, just above freezing, so this came as cold rain rather than snow. The tree’s sensors show the environment quickly growing wetter: the electrical conductivity of surface moisture spiked from 0.00 to 0.112 mS/cm as rainwater wetted the soil and sensor surfaces. Meanwhile, humidity rose – vapor pressure deficit dropped to ~0.2–0.3 kPa – indicating nearly saturated air, which would reduce any evaporative stress on the tree. Wind remained moderate (gusts 5–6 m/s) during the rain, so the precipitation thoroughly soaked the area without extreme wind desiccation. By the end of this event, the previously dry topsoil had absorbed water (evidenced by sustained non-zero EC readings through the afternoon), which likely eased water uptake for the tree’s roots. In the days after, nights returned to freezing (–6 °C on Mar 6–7), but the added soil moisture would temporarily alleviate drought conditions until the next weather shift.
Sunshine and Dry Air vs. Humid Calm Nights: The sensor data highlights a correlation between sunny, windy conditions and very dry air, contrasted with calm, humid nights – a dynamic important for the tree’s hydration. On February 27, under clear skies, solar radiation peaked near 480 W/m² late morning and brisk winds mixed the air (gusts ~8–10 m/s). The temperature rose to 9.6 °C, but the humidity lagged far behind – the vapor pressure was only 0.197 kPa, yielding a vapor pressure deficit ~0.99 kPa (extremely low relative humidity around midday). This indicates very desiccating air (on the order of 15–20% relative humidity), which can dry out exposed twigs and buds. The tree essentially experienced a mini “dry season” that afternoon, with no leaf wetness detected. In contrast, during nighttime or foggy periods when winds calmed, the station showed vapor pressure climbing and VPD dropping to zero, as on Mar 1 pre-dawn when dew formed. Thus, whenever the sun and wind peaked, the tree was subjected to drying conditions, and each night it was relieved by moisture either from dew or simply higher relative humidity. These short-term swings between dry afternoons and humid nights are characteristic of the late-winter climate and play a role in the tree’s daily water balance (even while leafless, the tree’s bark and buds exchange moisture with the air).
Long-Term Warming Trend and Snow Decline (Historical Context): The reanalysis climate data for the broader Gangwon region (1940–2024) puts this year’s winter in context. Late-winter temperatures have risen substantially over the decades – for example, the average March temperature in the mid-20th century (1940–1970) was around 0.5 °C, whereas in the 21st century (2001–2024) it’s about 3.3 °C. This ~3 °C warming means what used to be a frigid March is now often above freezing. Likewise, January has warmed by ~3.5 °C (from roughly –9.2 °C to –5.7 °C over the same period). A direct consequence is the reduction in snow cover. In the 1940s–60s, an average late winter month held about 20–27 mm of snow water equivalent on the ground (indicating persistent snowpack), but in recent decades that average is down to 12–14 mm. In other words, typical snowpack depth has roughly halved. The tree’s experience reflects this shift: during this 2025 late-winter period, there was no significant snow accumulation observed – precipitation came mostly as rain or brief flurries that didn’t linger. Historically, the tree might have been buried in snow for weeks; now it sees more open ground and rainfall in winter. Reduced insulating snow cover can expose the tree to deeper soil freezes but also allows earlier spring soil warming. The long-term trend suggests a gradually easing winter cold stress on the tree (fewer extreme subzero days) but also reduced water input from melting snow.
Recent Anomalies and Climate Extremes: While the overall climate is warming, year-to-year swings still produce anomalies that the tree must cope with. Notably, the past few years have shown how variable late winter can be. March 2023 was exceptionally mild in this region – the reanalysis indicates it averaged about 6.7 °C, making it the warmest March on record since at least 1940. In contrast, March 2024 was much colder (around 2.8 °C mean), and early March 2025 in our sensor data appears closer to the cold side (Feb 24–Mar 10 averaged roughly 0 °C). This year’s first half of March was almost a throwback to mid-20th-century conditions (when March means were ~0–1 °C), illustrating that despite the warming trend, cold winters can still occur. On the precipitation side, the region is prone to the occasional heavy snow even in a warming climate – for example, reanalysis data show March 2003 had an extraordinary late-season snowpack (peaking around 170 mm water equivalent, an extreme outlier). By comparison, Winter 2024–25 has been benign: no such extreme snowfall hit the Hongcheon area, and precipitation was relatively low. These historical comparisons highlight the tree’s resilience in the face of climate variability. It has endured both unusually warm winters and sudden cold, snowy episodes. The “stories” etched in the data – from dry sunshine to gale-blown snow and decades of climate shifts – collectively show a tree living through significant short-term shocks against a backdrop of long-term change.